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| author | Robert Ly <robertly@google.com> | 2011-09-25 12:14:19 -0700 |
|---|---|---|
| committer | Robert Ly <robertly@google.com> | 2011-10-17 15:27:55 -0700 |
| commit | 83a75a596587d2555acf8462af959895fab6579d (patch) | |
| tree | 39fcb6362e44bcb40a829bbfb1999e4d22ca8beb /docs | |
| parent | eaf4952410eb86d6ac8b343af3024250b9550dfd (diff) | |
| download | frameworks_base-83a75a596587d2555acf8462af959895fab6579d.zip frameworks_base-83a75a596587d2555acf8462af959895fab6579d.tar.gz frameworks_base-83a75a596587d2555acf8462af959895fab6579d.tar.bz2 | |
cherrypick from master - docs: nfc updates Change-Id: Iaa782911f14b11bc896ac9ef06db2c43104d1dac
Change-Id: Ic4bd26b3d95dbb98929736240a1907fccb937f88
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/html/guide/guide_toc.cs | 42 | ||||
| -rw-r--r-- | docs/html/guide/topics/nfc/advanced-nfc.jd | 303 | ||||
| -rw-r--r-- | docs/html/guide/topics/nfc/index.jd | 620 | ||||
| -rw-r--r-- | docs/html/guide/topics/nfc/nfc.jd | 922 | ||||
| -rw-r--r-- | docs/html/images/nfc_tag_dispatch.png | bin | 0 -> 64721 bytes |
5 files changed, 1275 insertions, 612 deletions
diff --git a/docs/html/guide/guide_toc.cs b/docs/html/guide/guide_toc.cs index f3540e2..b7710c3 100644 --- a/docs/html/guide/guide_toc.cs +++ b/docs/html/guide/guide_toc.cs @@ -262,20 +262,20 @@ </ul> </li> <li class="toggle-list"> - <div><a href="<?cs var:toroot ?>guide/topics/renderscript/index.html"> - <span class="en">RenderScript</span> - </a></div> - <ul> - <li><a href="<?cs var:toroot ?>guide/topics/renderscript/graphics.html"> - <span class="en">Graphics</span> - </a> - </li> - <li><a href="<?cs var:toroot ?>guide/topics/renderscript/compute.html"> - <span class="en">Compute</span> - </a> - </li> - </ul> - </li> + <div><a href="<?cs var:toroot ?>guide/topics/renderscript/index.html"> + <span class="en">RenderScript</span></a> + </div> + <ul> + <li><a href="<?cs var:toroot ?>guide/topics/renderscript/graphics.html"> + <span class="en">Graphics</span> + </a> + </li> + <li><a href="<?cs var:toroot ?>guide/topics/renderscript/compute.html"> + <span class="en">Compute</span> + </a> + </li> + </ul> + </li> <li class="toggle-list"> <div><a href="<?cs var:toroot ?>guide/topics/media/index.html"> @@ -332,9 +332,15 @@ <li><a href="<?cs var:toroot?>guide/topics/wireless/bluetooth.html"> <span class="en">Bluetooth</span></a> </li> - <li><a href="<?cs var:toroot?>guide/topics/nfc/index.html"> - <span class="en">Near Field Communication</span> - </a></li> + <li class="toggle-list"> + <div><a href="<?cs var:toroot?>guide/topics/nfc/index.html"> + <span class="en">Near Field Communication</span></a> <span class="new">updated</span> + </div> + <ul> + <li><a href="<?cs var:toroot ?>guide/topics/nfc/nfc.html">NFC Basics</a></li> + <li><a href="<?cs var:toroot ?>guide/topics/nfc/advanced-nfc.html">Advanced NFC</a></li> + </ul> + </li> <li class="toggle-list"> <div><a href="<?cs var:toroot?>guide/topics/usb/index.html"> <span class="en">USB</span></a> @@ -715,7 +721,7 @@ <li class="toggle-list"> <div><a href="<?cs var:toroot ?>guide/practices/ui_guidelines/index.html"> <span class="en">UI Guidelines</span> - </a></div> + </a> <span class="new-child">updated</span></div> <ul> <li class="toggle-list"> <div><a href="<?cs var:toroot ?>guide/practices/ui_guidelines/icon_design.html"> diff --git a/docs/html/guide/topics/nfc/advanced-nfc.jd b/docs/html/guide/topics/nfc/advanced-nfc.jd new file mode 100644 index 0000000..2b414aa --- /dev/null +++ b/docs/html/guide/topics/nfc/advanced-nfc.jd @@ -0,0 +1,303 @@ +page.title=Advanced NFC +@jd:body + +<div id="qv-wrapper"> +<div id="qv"> + <h2>In this document</h2> + <ol> + <li><a href="#tag-tech">Working with Supported Tag Technologies</a> + <ol> + <li><a href="#tech-intent">Working with tag technologies and the ACTION_TECH_DISCOVERED + intent</a></li> + <li><a href="#read-write">Reading and writing to tags</a></li> + </ol></li> + <li><a href="#foreground-dispatch">Using the Foreground Dispatch System</a></li> + </ol> +</div> +</div> + +<p>This document describes advanced NFC topics, such as working with various tag technologies, +writing to NFC tags, and foreground dispatching, which allows an application in the foreground to +handle intents even when other applications filter for the same ones.</p> + +<h2 id="tag-tech">Working with Supported Tag Technologies</h2> +<p>When working with NFC tags and Android-powered devices, the main format you use to read +and write data on tags is NDEF. When a device scans a tag with NDEF data, Android provides support +in parsing the message and delivering it in an {@link android.nfc.NdefMessage} when +possible. There are cases, however, when you scan a tag that does not contain +NDEF data or when the NDEF data could not be mapped to a MIME type or URI. +In these cases, you need to open communication directly with the tag and read and write to it with +your own protocol (in raw bytes). Android provides generic support for these use cases with the +{@link android.nfc.tech} package, which is described in <a href="#tech-table">Table 1</a>. You can +use the {@link android.nfc.Tag#getTechList getTechList()} method to determine the technologies +supported by the tag and create the corresponding {@link android.nfc.tech.TagTechnology} +object with one of classes provided by {@link android.nfc.tech} </p> + + +<table> + +<p class="table-caption" id="table1"> +<strong>Table 1.</strong> Supported tag technologies</p> +<table id="tech-table"> + + <tr> + <th>Class</th> + + <th>Description</th> + </tr> + + <tr> + <td>{@link android.nfc.tech.TagTechnology}</td> + + <td>The interface that all tag technology classes must implement.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.NfcA}</td> + + <td>Provides access to NFC-A (ISO 14443-3A) properties and I/O operations.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.NfcB}</td> + + <td>Provides access to NFC-B (ISO 14443-3B) properties and I/O operations.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.NfcF}</td> + + <td>Provides access to NFC-F (JIS 6319-4) properties and I/O operations.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.NfcV}</td> + + <td>Provides access to NFC-V (ISO 15693) properties and I/O operations.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.IsoDep}</td> + + <td>Provides access to ISO-DEP (ISO 14443-4) properties and I/O operations.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.Ndef}</td> + + <td>Provides access to NDEF data and operations on NFC tags that have been formatted as + NDEF.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.NdefFormatable}</td> + + <td>Provides a format operations for tags that may be NDEF formattable.</td> + </tr> + </table> +<p>The following tag technlogies are not required to be supported by Android-powered devices.</p> + <p class="table-caption" id="table2"> +<strong>Table 2.</strong> Optional supported tag technologies</p> + <table> + <tr> + <th>Class</th> + + <th>Description</th> + </tr> + <tr> + <td>{@link android.nfc.tech.MifareClassic}</td> + + <td>Provides access to MIFARE Classic properties and I/O operations, if this Android device + supports MIFARE.</td> + </tr> + + <tr> + <td>{@link android.nfc.tech.MifareUltralight}</td> + + <td>Provides access to MIFARE Ultralight properties and I/O operations, if this Android + device supports MIFARE.</td> + </tr> + </table> + +<h3 id="tech-intent">Working with tag technologies and the ACTION_TECH_DISCOVERED intent</h3> +<p>When a device scans a tag that has NDEF data on it, but could not be mapped to a MIME or URI, +the tag dispatch system tries to start an activity with the {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} +intent. The {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} is also used when a tag +with non-NDEF data is scanned. Having this fallback allows you to work with the data on the tag +directly if the tag dispatch system could not parse it for you. The basic steps when working with +tag technologies are as follows:</p> + +<ol> + <li>Filter for an {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent specifying the +tag technologies that you want to handle. See <a +href="{@docRoot}guide/topics/nfc/nfc.html#tech-disc">Filtering for NFC +intents</a> for more information. In general, the tag dispatch system tries to start a {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent when an NDEF message +cannot be mapped to a MIME type or URI, or if the tag scanned did not contain NDEF data. For +more information on how this is determined, see <a +href="{@docRoot}guide/topics/nfc/nfc.html#tag-dispatch">The Tag Dispatch System</a>.</li> + <li>When your application receives the intent, obtain the {@link android.nfc.Tag} object from +the intent: +<pre>Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);</pre></li> +<li>Obtain an instance of a {@link android.nfc.tech.TagTechnology}, by calling one of the +<code>get</code> factory methods of the classes in the {@link android.nfc.tech} package. You can +enumerate the supported technologies of the tag by calling {@link android.nfc.Tag#getTechList +getTechList()} before calling a <code>get</code> factory method. For example, to obtain an instance +of {@link android.nfc.tech.MifareUltralight} from a {@link android.nfc.Tag}, do the following: + +<pre> +MifareUltralight.get(intent.getParcelableExtra(NfcAdapter.EXTRA_TAG)); +</pre> +</li> +</ol> + + + +<h3 id="read-write">Reading and writing to tags</h3> + +<p>Reading and writing to an NFC tag involves obtaining the tag from the intent and +opening communication with the tag. You must define your own protocol stack to read and write data +to the tag. Keep in mind, however, that you can still read and write NDEF data when working +directly with a tag. It is up to you how you want to structure things. The +following example shows how to work with a MIFARE Ultralight tag.</p> + +<pre> +package com.example.android.nfc; + +import android.nfc.Tag; +import android.nfc.tech.MifareUltralight; +import android.util.Log; +import java.io.IOException; +import java.nio.charset.Charset; + +public class MifareUltralightTagTester { + + private static final String TAG = MifareUltralightTagTester.class.getSimpleName(); + + public void writeTag(Tag tag, String tagText) { + MifareUltralight ultralight = MifareUltralight.get(tag); + try { + ultralight.connect(); + ultralight.writePage(4, "abcd".getBytes(Charset.forName("US-ASCII"))); + ultralight.writePage(5, "efgh".getBytes(Charset.forName("US-ASCII"))); + ultralight.writePage(6, "ijkl".getBytes(Charset.forName("US-ASCII"))); + ultralight.writePage(7, "mnop".getBytes(Charset.forName("US-ASCII"))); + } catch (IOException e) { + Log.e(TAG, "IOException while closing MifareUltralight...", e); + } finally { + try { + ultralight.close(); + } catch (IOException e) { + Log.e(TAG, "IOException while closing MifareUltralight...", e); + } + } + } + + public String readTag(Tag tag) { + MifareUltralight mifare = MifareUltralight.get(tag); + try { + mifare.connect(); + byte[] payload = mifare.readPages(4); + return new String(payload, Charset.forName("US-ASCII")); + } catch (IOException e) { + Log.e(TAG, "IOException while writing MifareUltralight + message...", e); + } finally { + if (mifare != null) { + try { + mifare.close(); + } + catch (IOException e) { + Log.e(TAG, "Error closing tag...", e); + } + } + } + return null; + } +} +</pre> + +</pre> + + <h2 id="foreground-dispatch">Using the Foreground Dispatch System</h2> + + <p>The foreground dispatch system allows an activity to intercept an intent and claim +priority over other activities that handle the same intent. Using this system involves + constructing a few data structures for the Android system to be able to send the appropriate + intents to your application. To enable the foreground dispatch system:</p> + + <ol> + <li>Add the following code in the <code>onCreate()</code> method of your activity: + + <ol type="a"> + <li>Create a {@link android.app.PendingIntent} object so the Android system can populate it + with the details of the tag when it is scanned. + <pre> +PendingIntent pendingIntent = PendingIntent.getActivity( + this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0); +</pre> + </li> + + <li>Declare intent filters to handle the intents that you want to intercept. The foreground + dispatch system checks the specified intent filters with the intent that is received when + the device scans a tag. If it matches, then your application handles the intent. If it does + not match, the foreground dispatch system falls back to the intent dispatch system. + Specifying a <code>null</code> array of intent filters and technology filters, specifies + that you want to filter for all tags that fallback to the <code>TAG_DISCOVERED</code> + intent. The code snippet below handles all MIME types for <code>NDEF_DISCOVERED</code>. You + should only handle the ones that you need. +<pre> +IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED); + try { + ndef.addDataType("*/*"); /* Handles all MIME based dispatches. + You should specify only the ones that you need. */ + } + catch (MalformedMimeTypeException e) { + throw new RuntimeException("fail", e); + } + intentFiltersArray = new IntentFilter[] {ndef, }; +</pre> + </li> + + <li>Set up an array of tag technologies that your application wants to handle. Call the + <code>Object.class.getName()</code> method to obtain the class of the technology that you + want to support. +<pre> +techListsArray = new String[][] { new String[] { NfcF.class.getName() } }; +</pre> + </li> + </ol> + </li> + + <li>Override the following activity lifecycle callbacks and add logic to enable and disable the + foreground dispatch when the activity loses ({@link android.app.Activity#onPause onPause()}) + and regains ({@link android.app.Activity#onResume onResume()}) focus. {@link + android.nfc.NfcAdapter#enableForegroundDispatch enableForegroundDispatch()} must be called from +the main thread and only when the activity is in the foreground (calling in {@link +android.app.Activity#onResume onResume()} guarantees this). You also need to implement the {@link + android.app.Activity#onNewIntent onNewIntent} callback to process the data from the scanned NFC + tag.</li> + +<pre> +public void onPause() { + super.onPause(); + mAdapter.disableForegroundDispatch(this); +} + +public void onResume() { + super.onResume(); + mAdapter.enableForegroundDispatch(this, pendingIntent, intentFiltersArray, techListsArray); +} + +public void onNewIntent(Intent intent) { + Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG); + //do something with tagFromIntent +} +</pre> + </li> + </ol> + + <p>See the <a href= +"{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/nfc/ForegroundDispatch.html"> +ForegroundDispatch</a> sample from API Demos for the complete sample.</p>
\ No newline at end of file diff --git a/docs/html/guide/topics/nfc/index.jd b/docs/html/guide/topics/nfc/index.jd index b486d3b..b86d72d 100644 --- a/docs/html/guide/topics/nfc/index.jd +++ b/docs/html/guide/topics/nfc/index.jd @@ -1,601 +1,33 @@ page.title=Near Field Communication @jd:body -<div id="qv-wrapper"> -<div id="qv"> - <h2>In this document</h2> - <ol> - <li><a href="#api">API Overview</a></li> - <li><a href="#manifest">Declaring Android Manifest elements</a></li> - <li><a href="#dispatch">The Tag Dispatch System</a> - <ol> - <li><a href="#intent-dispatch">Using the intent dispatch system</a></li> - <li><a href="#foreground-dispatch">Using the foreground dispatch system</a></li> - </ol></li> - <li><a href="#ndef">Working with Data on NFC Tags</a></li> - <li><a href="#read">Reading an NFC Tag</a></li> - <li><a href="#write">Writing to an NFC Tag</a></li> - <li><a href="#p2p">Peer-to-Peer Data Exchange</a></li> - </ol> -</div> -</div> - <p>Near Field Communication (NFC) is a set of short-range wireless technologies, typically - requiring a distance of 4cm or less. NFC operates at 13.56mhz, and at rates ranging from 106 - kbit/s to 848 kbit/s. NFC communication always involves an initiator and a target. The initiator - actively generates an RF field that can power a passive target. This enables NFC targets to take - very simple form factors such as tags, stickers or cards that do not require power. NFC - peer-to-peer communication is also possible, where both devices are powered.</p> - - <p>Compared to other wireless technologies such as Bluetooth or WiFi, NFC provides much lower - bandwidth and range, but enables low-cost, un-powered targets and does not require discovery or - pairing. Interactions can be initiated with just a tap.</p> + requiring a distance of 4cm or less to initiate a connection. NFC allows you to share small + payloads of data between an NFC tag and an Android-powered device, or between two Android-powered + devices. - <p>An Android device with NFC hardware will typically act as an initiator when the screen is on. - This mode is also known as NFC reader/writer. It will actively look for NFC tags and start - activities to handle them. Android 2.3.3 also has some limited P2P support.</p> - - <p>Tags can range in complexity, simple tags just offer read/write semantics, sometimes with + <p>Tags can range in complexity. Simple tags offer just read and write semantics, sometimes with one-time-programmable areas to make the card read-only. More complex tags offer math operations, and have cryptographic hardware to authenticate access to a sector. The most sophisticated tags - contain operating environments, allowing complex interactions with code executing on the tag.</p> - - <h2 id="api">API Overview</h2> - - <p>The {@link android.nfc} package contains the high-level classes to interact with the local - device's NFC adapter, to represent discovered tags, and to use the NDEF data format.</p> - - <table> - <tr> - <th>Class</th> - - <th>Description</th> - </tr> - - <tr> - <td>{@link android.nfc.NfcManager}</td> - - <td>A high level manager class that enumerates the NFC adapters on this Android device. Since - most Android devices only have one NFC adapter, you can just use the static helper {@link - android.nfc.NfcAdapter#getDefaultAdapter(Context)} for most situations.</td> - </tr> - - <tr> - <td>{@link android.nfc.NfcAdapter}</td> - - <td>Represents the local NFC adapter. Defines the intent's used to request tag dispatch to - your activity, and provides methods to register for foreground tag dispatch and foreground - NDEF push. Foreground NDEF push is the only peer-to-peer support that is currently provided - in Android.</td> - </tr> - - <tr> - <td>{@link android.nfc.NdefMessage} and {@link android.nfc.NdefRecord}</td> - - <td>NDEF is an NFC Forum defined data structure, designed to efficiently store data on NFC - tags, such as text, URL's, and other MIME types. A {@link android.nfc.NdefMessage} acts as a - container for the data that you want to transmit or read. One {@link android.nfc.NdefMessage} - object contains zero or more {@link android.nfc.NdefRecord}s. Each NDEF record has a type - such as text, URL, smart poster, or any MIME data. The type of the first NDEF record in the - NDEF message is used to dispatch a tag to an activity on Android.</td> - </tr> - - <tr> - <td>{@link android.nfc.Tag}</td> - - <td>Represents a passive NFC target. These can come in many form factors such as a tag, card, - key fob, or even a phone doing card emulation. When a tag is discovered, a {@link - android.nfc.Tag} object is created and wrapped inside an Intent. The NFC dispatch system - sends the intent to a compatible activity using <code>startActivity()</code>. You can use the - {@link android.nfc.Tag#getTechList getTechList()} method to determine the technologies - supported by this tag and create the corresponding {@link android.nfc.tech.TagTechnology} - object with one of classes provided by {@link android.nfc.tech}.</td> - </tr> - </table> - - <p>The {@link android.nfc.tech} package contains classes to query properties and perform I/O - operations on a tag. The classes are divided to represent different NFC technologies that can be - available on a Tag:</p> - - <table> - <tr> - <th>Class</th> - - <th>Description</th> - </tr> - - <tr> - <td>{@link android.nfc.tech.TagTechnology}</td> - - <td>The interface that all tag technology classes must implement.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.NfcA}</td> - - <td>Provides access to NFC-A (ISO 14443-3A) properties and I/O operations.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.NfcB}</td> - - <td>Provides access to NFC-B (ISO 14443-3B) properties and I/O operations.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.NfcF}</td> - - <td>Provides access to NFC-F (JIS 6319-4) properties and I/O operations.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.NfcV}</td> - - <td>Provides access to NFC-V (ISO 15693) properties and I/O operations.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.IsoDep}</td> - - <td>Provides access to ISO-DEP (ISO 14443-4) properties and I/O operations.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.Ndef}</td> - - <td>Provides access to NDEF data and operations on NFC tags that have been formatted as - NDEF.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.NdefFormatable}</td> - - <td>Provides a format operations for tags that may be NDEF formattable.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.MifareClassic}</td> - - <td>Provides access to MIFARE Classic properties and I/O operations, if this Android device - supports MIFARE.</td> - </tr> - - <tr> - <td>{@link android.nfc.tech.MifareUltralight}</td> - - <td>Provides access to MIFARE Ultralight properties and I/O operations, if this Android - device supports MIFARE.</td> - </tr> - </table> - - <h2 id="manifest">Declaring Android Manifest elements</h2> - - <p>Before you can access a device's NFC hardware and properly handle NFC intents, declare these - items in your <code>AndroidManifest.xml</code> file:</p> - - <ol> - <li>The NFC <code><uses-permission></code> element to access the NFC hardware: - <pre> -<uses-permission android:name="android.permission.NFC" /> -</pre> - </li> - - <li>The minimum SDK version that your application can support. API level 9 only supports - limited tag dispatch via {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}, and only gives - access to NDEF messages via the {@link android.nfc.NfcAdapter#EXTRA_NDEF_MESSAGES} extra. No - other tag properties or I/O operations are accessible. You probably want to use API level 10 - which includes comprehensive reader/writer support. - <pre class="pretty-print"> -<uses-sdk android:minSdkVersion="10"/> -</pre> - </li> - - <li>The uses-feature element so that your application can show up in the Android Market for - devices that have NFC hardware: - <pre> -<uses-feature android:name="android.hardware.nfc" android:required="true" /> -</pre> - </li> - - <li>The NFC intent filter to tell the Android system your Activity can handle NFC data. Specify - one or more of these three intent filters: - <pre> -<intent-filter> - <action android:name="android.nfc.action.NDEF_DISCOVERED"/> - <data android:mimeType="<em>mime/type</em>" /> -</intent-filter> - -<intent-filter> - <action android:name="android.nfc.action.TECH_DISCOVERED"/> - <meta-data android:name="android.nfc.action.TECH_DISCOVERED" - android:resource="@xml/<em>nfc_tech_filter</em>.xml" /> -</intent-filter> - -<intent-filter> - <action android:name="android.nfc.action.TAG_DISCOVERED"/> -</intent-filter> -</pre> - - <p>The three intent filters are prioritized and behave in specific ways. Declare only the - ones that your Activity needs to handle. For more information on how to handle these filters, - see the section about <a href="#dispatch">The Tag Dispatch System</a>.</p> - </li> - </ol> - - <p>View the <a href= - "../../../resources/samples/NFCDemo/AndroidManifest.html">AndroidManifest.xml</a> from the - NFCDemo sample to see a complete example.</p> - - <h2 id="dispatch">The Tag Dispatch System</h2> - - <p>When an Android device scans an NFC tag, the desired behavior is to have the most appropriate - Activity handle the intent without asking the user what application to use. Because devices scan - NFC tags at a very short range, it is likely that making users manually select an Activity forces - them to move the device away from the tag and break the connection. You should develop your - Activity to only handle the NFC tags that your Activity cares about to prevent the Activity - Chooser from appearing. Android provides two systems to help you correctly identify an NFC tag - that your Activity should handle: the Intent dispatch system and the foreground Activity dispatch - system.</p> - - <p>The intent dispatch system checks the intent filters of all the Activities along with the - types of data that the Activities support to find the best Activity that can handle the NFC tag. - If multiple Activities specify the same intent filter and data to handle, then the Activity - Chooser is presented to the user as a last resort.</p> - - <p>The foreground dispatch system allows an Activity application to override the intent dispatch - system and have priority when an NFC tag is scanned. The Activity handling the request must be - running in the foreground of the device. When an NFC tag is scanned and matches the intent and - data type that the foreground dispatch Activity defines, the intent is immediately sent to the - Activity even if another Activity can handle the intent. If the Activity cannot handle the - intent, the foreground dispatch system falls back to the intent dispatch system.</p> - - <h3 id="intent-dispatch">Using the intent dispatch system</h3> - - <p>The intent dispatch system specifies three intents that each have a priority. The intents that - start when a device scans a tag depend on the type of tag scanned. In general, the intents are - started in the following manner:</p> - - <ul> - <li> - <code>android.nfc.action.NDEF_DISCOVERED</code>: This intent starts when a tag that contains - an NDEF payload is scanned. This is the highest priority intent. The Android system does not - let you specify this intent generically to handle all data types. You must specify - <code><data></code> elements in the <code>AndroidManifest.xml</code> along with this - intent to correctly handle NFC tags that start this intent. For example, to handle a - <code>NDEF_DISCOVERED</code> intent that contains plain text, specify the following filter in - your <code>AndroidManifest.xml</code> file: - <pre> -<intent-filter> - <action android:name="android.nfc.action.NDEF_DISCOVERED"/> - <data android:mimeType="text/plain" /> -</intent-filter> -</pre> - - <p>If the <code>NDEF_DISCOVERED</code> intent is started, the <code>TECH_DISCOVERED</code> - and <code>TAG_DISCOVERED</code> intents are not started. This intent does not start if an - unknown tag is scanned or if the tag does not contain an NDEF payload.</p> - </li> - - <li><code>android.nfc.action.TECH_DISCOVERED</code>: If the <code>NDEF_DISCOVERED</code> intent - does not start or is not filtered by any Activity on the device, this intent starts if the tag - is known. The <code>TECH_DISCOVERED</code> intent requires that you specify the technologies - that you want to support in an XML resource file. For more information, see the section about - <a href="#technology-resources">Specifying tag technologies to handle</a>.</li> - - <li><code>android.nfc.action.TAG_DISCOVERED</code>: This intent starts if no Activities handle - the <code>NDEF_DISCOVERED</code> and <code>TECH_DISCOVERED</code> intents or if the tag that is - scanned is unknown.</li> - </ul> - - <h4 id="tech">Specifying tag technologies to handle</h4> - - <p>If your Activity declares the <code>android.nfc.action.TECH_DISCOVERED</code> intent in your - <code>AndroidManifest.xml</code> file, you must create an XML resource file that specifies the - technologies that your Activity supports within a <code>tech-list</code> set. Your Activity is - considered a match if a <code>tech-list</code> set is a subset of the technologies that are - supported by the tag, which you can obtain by calling {@link android.nfc.Tag#getTechList - getTechList()}.</p> - - <p>For example, if the tag that is scanned supports MifareClassic, NdefFormatable, and NfcA, your - <code>tech-list</code> set must specify all three, two, or one of the technologies (and nothing - else) in order for your Activity to be matched.</p> - - <p>The following sample defines all of the technologies. You can remove the ones that you do not - need. Save this file (you can name it anything you wish) in the - <code><project-root>/res/xml</code> folder.</p> - <pre> -<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> - <tech-list> - <tech>android.nfc.tech.IsoDep</tech> - <tech>android.nfc.tech.NfcA</tech> - <tech>android.nfc.tech.NfcB</tech> - <tech>android.nfc.tech.NfcF</tech> - <tech>android.nfc.tech.NfcV</tech> - <tech>android.nfc.tech.Ndef</tech> - <tech>android.nfc.tech.NdefFormatable</tech> - <tech>android.nfc.tech.MifareClassic</tech> - <tech>android.nfc.tech.MifareUltralight</tech> - </tech-list> -</resources> -</pre> - - <p>You can also specify multiple <code>tech-list</code> sets. Each of the <code>tech-list</code> - sets is considered independently, and your Activity is considered a match if any single - <code>tech-list</code> set is a subset of the technologies that are returned by {@link - android.nfc.Tag#getTechList getTechList()}. This provides <code>AND</code> and <code>OR</code> - semantics for matching technologies. The following example matches tags that can support the - NfcA and Ndef technologies or can support the NfcB and Ndef technologies:</p> - <pre> -<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> - <tech-list> - <tech>android.nfc.tech.NfcA</tech> - <tech>android.nfc.tech.Ndef</tech> - </tech-list> -</resources> - -<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> - <tech-list> - <tech>android.nfc.tech.NfcB</tech> - <tech>android.nfc.tech.Ndef</tech> - </tech-list> -</resources> -</pre> - - <p>In your <code>AndroidManifest.xml</code> file, specify the resource file that you just created - in the <code><meta-data></code> element inside the <code><activity></code> - element like in the following example:</p> - <pre> -<activity> -... -<intent-filter> - <action android:name="android.nfc.action.TECH_DISCOVERED"/> -</intent-filter> - -<meta-data android:name="android.nfc.action.TECH_DISCOVERED" - android:resource="@xml/nfc_tech_filter" /> -... -</activity> -</pre> - - <h3 id="foreground-dispatch">Using the foreground dispatch system</h3> - - <p>The foreground dispatch system allows an Activity to intercept an intent and claim priority - over other Activities that handle the same intent. The system is easy to use and involves - constructing a few data structures for the Android system to be able to send the appropriate - intents to your application. To enable the foreground dispatch system:</p> - - <ol> - <li>Add the following code in the onCreate() method of your Activity: - - <ol type="a"> - <li>Create a {@link android.app.PendingIntent} object so the Android system can populate it - with the details of the tag when it is scanned - <pre> -PendingIntent pendingIntent = PendingIntent.getActivity( - this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0); -</pre> - </li> - - <li>Declare intent filters to handle the intents that you want to intercept. The foreground - dispatch system checks the specified intent filters with the intent that is received when - the device scans a tag. If they match, then your application handles the intent. If it does - not match, the foreground dispatch system falls back to the intent dispatch system. - Specifying a <code>null</code> array of intent filters and for the technology filters, you - receive a <code>TAG_DISCOVERED</code> intent for all tags discovered. Note that the snippet - below handles all MIME types. You should only handle the ones that you need. - <pre> - IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED); - try { - ndef.addDataType("*/*"); /* Handles all MIME based dispatches. - You should specify only the ones that you need. */ - } - catch (MalformedMimeTypeException e) { - throw new RuntimeException("fail", e); - } - intentFiltersArray = new IntentFilter[] { - ndef, - }; -</pre> - </li> - - <li>Set up an array of tag technologies that your application wants to handle. Call the - <code>Object.class.getName()</code> method to obtain the class of the technology that you - want to support. - <pre> - - techListsArray = new String[][] { new String[] { NfcF.class.getName() } }; - -</pre> - </li> - </ol> - </li> - - <li>Override the following Activity lifecycle callbacks and add logic to enable and disable the - foreground dispatch when the Activity loses ({@link android.app.Activity#onPause onPause()}) - and regains ({@link android.app.Activity#onResume onResume()}) focus. {@link - android.nfc.NfcAdapter#enableForegroundDispatch} must be called from the main thread and only - when the activity is in the foreground (calling in {@link android.app.Activity#onResume - onResume()} guarantees this). You also need to implement the {@link - android.app.Activity#onNewIntent onNewIntent} callback to process the data from the scanned NFC - tag. - <pre> -public void onPause() { - super.onPause(); - mAdapter.disableForegroundDispatch(this); -} - -public void onResume() { - super.onResume(); - mAdapter.enableForegroundDispatch(this, pendingIntent, intentFiltersArray, techListsArray); -} - -public void onNewIntent(Intent intent) { - Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG); - //do something with tagFromIntent -} -</pre> - </li> - </ol> - - <p>See the <a href= - "{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/nfc/ForegroundDispatch.html">ForegroundDispatch</a> - sample from API Demos for the complete sample.</p> - - <h2 id="ndef">Working with Data on NFC Tags</h2> - - <p>Data on NFC tags are encoded in raw bytes, so you must convert the bytes to something human - readable if you are presenting the data to the user. When writing to NFC tags, you must write - them in bytes as well. Android provides APIs to help write messages that conform to the NDEF - standard, which was developed by the <a href="http://www.nfc-forum.org/specs/">NFC Forum</a> to - standardized data on tags. Using this standard ensures that your data will be supported by all - Android NFC devices if you are writing to tags. However, many tag technologies use their own - standard for storing data and are supported by Android as well, but you have to implement your - own protocol stack to read and write to these tags. You can find a full list of the supported - technologies in {@link android.nfc.tech} and an overview of the technologies in the {@link - android.nfc.tech.TagTechnology} interface. This section is a brief overview of how to work with - NDEF messages in the context of the Android system. It is not meant to be a complete discussion - of the NDEF specification, but highlights the main things that you need to be aware of when - working with NDEF messages in Android.</p> - - <p>To facilitate working with NDEF messages, Android provides the {@link android.nfc.NdefRecord} - and {@link android.nfc.NdefMessage} to encapsulate the raw bytes that represent NDEF messages. An - {@link android.nfc.NdefMessage} is the container for zero or more {@link - android.nfc.NdefRecord}s. Each {@link android.nfc.NdefRecord} has its own unique type name - format, record type, and ID to distinguish them from other records within the same {@link - android.nfc.NdefMessage}. You can store different types of records of varying length in a single - {@link android.nfc.NdefMessage}. The size constraint of the NFC tag determines how big your - {@link android.nfc.NdefMessage} can be.</p> - - <p>Tags that support the {@link android.nfc.tech.Ndef} and {@link - android.nfc.tech.NdefFormatable} technologies return and accept {@link android.nfc.NdefMessage} - objects as parameters for read and write operations. You need to create your own logic to read - and write bytes for other tag technologies in {@link android.nfc.tech}.</p> - - <p>You can download technical specifications for different types of NDEF message standards, such - as plain text and Smart Posters, at the <a href="http://www.nfc-forum.org/specs/">NFC Forum</a> - website. The NFCDemo sample application also declares sample <a href= - "{@docRoot}resources/samples/NFCDemo/src/com/example/android/nfc/simulator/MockNdefMessages.html"> - plain text and SmartPoster NDEF messages.</a></p> - - <h2 id="read">Reading an NFC Tag</h2> - - <p>When a device comes in proximity to an NFC tag, the appropriate intent is started on the - device, notifying interested applications that a NFC tag was scanned. By previously declaring the - appropriate intent filter in your <code>AndroidManifest.xml</code> file or using foreground - dispatching, your application can request to handle the intent.</p> - - <p>The following method (slightly modified from the NFCDemo sample application), handles the - <code>TAG_DISCOVERED</code> intent and iterates through an array obtained from the intent that - contains the NDEF payload:</p> - <pre> -NdefMessage[] getNdefMessages(Intent intent) { - // Parse the intent - NdefMessage[] msgs = null; - String action = intent.getAction(); - if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)) { - Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES); - if (rawMsgs != null) { - msgs = new NdefMessage[rawMsgs.length]; - for (int i = 0; i < rawMsgs.length; i++) { - msgs[i] = (NdefMessage) rawMsgs[i]; - } - } - else { - // Unknown tag type - byte[] empty = new byte[] {}; - NdefRecord record = new NdefRecord(NdefRecord.TNF_UNKNOWN, empty, empty, empty); - NdefMessage msg = new NdefMessage(new NdefRecord[] {record}); - msgs = new NdefMessage[] {msg}; - } - } - else { - Log.e(TAG, "Unknown intent " + intent); - finish(); - } - return msgs; -} -</pre> - - <p>Keep in mind that the data that the device reads is in bytes, so you must implement your own - logic if you need to present the data in a readable format to the user. The classes in - <code>com.example.android.nfc.record</code> of the NFCDemo sample show you how to parse some - common types of NDEF messages such as plain text or a SmartPoster.</p> - - <h2 id="write">Writing to an NFC Tag</h2> - - <p>Writing to an NFC tag involves constructing your NDEF message in bytes and using the - appropriate tag technology for the tag that you are writing to. The following code sample shows - you how to write a simple text message to a {@link android.nfc.tech.NdefFormatable} tag:</p> - <pre> -NdefFormatable tag = NdefFormatable.get(t); -Locale locale = Locale.US; -final byte[] langBytes = locale.getLanguage().getBytes(Charsets.US_ASCII); -String text = "Tag, you're it!"; -final byte[] textBytes = text.getBytes(Charsets.UTF_8); -final int utfBit = 0; -final char status = (char) (utfBit + langBytes.length); -final byte[] data = Bytes.concat(new byte[] {(byte) status}, langBytes, textBytes); -NdefRecord record = NdefRecord(NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_TEXT, new byte[0], data); -try { - NdefRecord[] records = {text}; - NdefMessage message = new NdefMessage(records); - tag.connect(); - tag.format(message); -} -catch (Exception e){ - //do error handling -} -</pre> - - <h2 id="p2p">Peer-to-Peer Data Exchange</h2> - - <p>Support for simple peer-to-peer data exchange is supported by the foreground push feature, - which is enabled with the {@link android.nfc.NfcAdapter#enableForegroundNdefPush} method. To use - this feature:</p> - - <ul> - <li>The Activity that is pushing the data must be in the foreground</li> - - <li>You must encapsulate the data that you are sending in an {@link android.nfc.NdefMessage} - object</li> - - <li>The NFC device that is receiving the pushed data (the scanned device) must support the - <code>com.android.npp</code> NDEF push protocol, which is optional for Android devices.</li> - </ul> - - <p class="note">If your Activity enables the foreground push feature and is in the foreground, - the standard intent dispatch system is disabled. However, if your Activity also enables - foreground dispatching, then it can still scan tags that match the intent filters set in the - foreground dispatching.</p> - - <p>To enable foreground dispatching:</p> - - <ol> - <li>Create an NdefMessage that contains the NdefRecords that you want to push onto the other - device.</li> - - <li>Implement the {@link android.app.Activity#onResume onResume()} and {@link - android.app.Activity#onPause onPause()} callbacks in your Activity to appropriately handle the - foreground pushing lifecycle. You must call {@link - android.nfc.NfcAdapter#enableForegroundNdefPush} from the main thread and only when the - activity is in the foreground (calling in {@link android.app.Activity#onResume onResume()} - guarantees this). - <pre> -public void onResume() { - super.onResume(); - if (mAdapter != null) - mAdapter.enableForegroundNdefPush(this, myNdefMessage); -} -public void onPause() { - super.onPause(); - if (mAdapter != null) - mAdapter.disableForegroundNdefPush(this); -} -</pre> - </li> - </ol> - - <p>When the Activity is in the foreground, you can now tap the device to another device and push - the data to it. See the <a href= - "../../../resources/samples/ApiDemos/src/com/example/android/apis/nfc/ForegroundNdefPush.html">ForegroundNdefPush</a> - sample in API Demos for a simple example of peer-to-peer data exchange.</p>
\ No newline at end of file + contain operating environments, allowing complex interactions with code executing on the tag. + The data stored in the tag can also be written in a variety of formats, but many of the Android + framework APIs are based around a <a href="http://www.nfc-forum.org/">NFC Forum</a> standard + called NDEF (NFC Data Exchange Format).</p> + + <dl> + <dt><strong><a href="{@docRoot}guide/topics/nfc/nfc.html">NFC Basics</a></strong></dt> + <dd>This document describes how Android handles discovered NFC tags and how it notifies +applications of data that is relevant to the application. It also goes over how to work with the +NDEF data in your applications and gives an overview of the framework APIs that support the basic +NFC feature set of Android.</dd> + + <dt><strong><a href="{@docRoot}guide/topics/nfc/advanced-nfc.html">Advanced + NFC</a></strong></dt> + <dd>This document goes over the APIs that enable use of the various tag technologies that + Android supports. When you are not working with NDEF data, or when you are working with NDEF + data that Android cannot fully understand, you have to manually read or write to the tag in raw + bytes using your own protocol stack. In these cases, Android provides support to detect + certain tag technologies and to open communication with the tag using your own protocol + stack.</dd> + </dl> +</p>
\ No newline at end of file diff --git a/docs/html/guide/topics/nfc/nfc.jd b/docs/html/guide/topics/nfc/nfc.jd new file mode 100644 index 0000000..892e418 --- /dev/null +++ b/docs/html/guide/topics/nfc/nfc.jd @@ -0,0 +1,922 @@ +page.title=NFC Basics +@jd:body + + +<div id="qv-wrapper"> +<div id="qv"> + <h2>In this document</h2> + <ol> + <li><a href="#tag-dispatch">The Tag Dispatch System</a> + <ol> + <li><a href="#ndef">How NFC tags are mapped to MIME types and URIs</a></li> + <li><a href="#dispatching">How NFC Tags are Dispatched to Applications</a></li> + </ol> + </li> + <li><a href="#filtering-intents">Filtering for Intents</a> + <ol> + <li><a href="#ndef-disc">ACTION_NDEF_DISCOVERED</a></li> + <li><a href="#tech-disc">ACTION_TECH_DISCOVERED</a></li> + <li><a href="#tag-disc">ACTION_TAG_DISCOVERED</a></li> + <li><a href="#obtain-info">Obtaining information from intents</a></li> + </ol> + </li> + <li><a href="#creating-records">Creating Common Types of NDEF Records</a> + <ol> + <li><a href="#abs-uri">TNF_ABSOLUTE_URI</a></li> + <li><a href="#mime">TNF_MIME_MEDIA</a></li> + <li><a href="#well-known-text">TNF_WELL_KNOWN with RTD_TEXT</a></li> + <li><a href="#well-known-uri">TNF_WELL_KNOWN with RTD_URI</a></li> + <li><a href="#ext-type">TNF_EXTERNAL_TYPE</a></li> + <li><a href="#aar">Android Application Records</a></li> + </ol> + </li> + <li><a href="#p2p">Beaming NDEF Messages to Other Devices</a></li> + </ol> +</div> +</div> + +<p>This document describes the basic NFC tasks you perform in Android. It explains how to send and +receive NFC data in the form of NDEF messages and describes the Android framework APIs that support +these features. For more advanced topics, including a discussion of working with non-NDEF data, +see <a href="{@docRoot}guide/topics/nfc/advanced-nfc.html">Advanced NFC</a>.</p> + + +<p>There are two major uses cases when working with NDEF data and Android:</p> + +<ul> + <li>Reading NDEF data from an NFC tag</li> + <li>Beaming NDEF messages from one device to another with <a href="#p2p">Android +Beam™</a></li> +</ul> + + +<p>Reading NDEF data from an NFC tag is handled with the <a href="#tag-dispatch">tag dispatch +system</a>, which analyzes discovered NFC tags, appropriately categorizes the data, and starts +an application that is interested in the categorized data. An application that wants to handle the +scanned NFC tag can <a href="#filtering-intents">declare an intent filter</a> and +request to handle the data.</p> + +<p>The Android Beam™ feature allows a device to push an NDEF message onto +another device by physically tapping the devices together. This interaction provides an easier way +to send data than other wireless technologies like Bluetooth, because with NFC, no manual device +discovery or pairing is required. The connection is automatically started when two devices come +into range. Android Beam is available through a set of NFC APIs, so any application can transmit +information between devices. For example, the Contacts, Browser, and YouTube applications use +Android Beam to share contacts, web pages, and videos with other devices. +</p> + + +<h2 id="tag-dispatch">The Tag Dispatch System</h2> + +<p>Android-powered devices are usually looking for NFC tags when the screen +is unlocked, unless NFC is disabled in the device's Settings menu. +When an Android-powered device discovers an NFC tag, the desired behavior +is to have the most appropriate activity handle the intent without asking the user what application +to use. Because devices scan NFC tags at a very short range, it is likely that making users manually +select an activity would force them to move the device away from the tag and break the connection. +You should develop your activity to only handle the NFC tags that your activity cares about to +prevent the Activity Chooser from appearing.</p> + +<p>To help you with this goal, Android provides a special tag dispatch system that analyzes scanned +NFC tags, parses them, and tries to locate applications that are interested in the scanned data. It +does this by:</p> + +<ol> + <li>Parsing the NFC tag and figuring out the MIME type or a URI that identifies the data payload + in the tag.</li> + <li>Encapsulating the MIME type or URI and the payload into an intent. These first two + steps are described in <a href="#ndef">How NFC tags are mapped to MIME types and URIs</a>.</li> + <li>Starts an activity based on the intent. This is described in + <a href="#dispatching">How NFC Tags are Dispatched to Applications</a>.</li> +</ol> + +<h3 id="ndef">How NFC tags are mapped to MIME types and URIs</h3> +<p>Before you begin writing your NFC applications, it is important to understand the different +types of NFC tags, how the tag dispatch system parses NFC tags, and the special work that the tag +dispatch system does when it detects an NDEF message. NFC tags come in a +wide array of technologies and can also have data written to them in many different ways. +Android has the most support for the NDEF standard, which is defined by the <a +href="http://www.nfc-forum.org/home">NFC Forum</a>. +</p> + +<p>NDEF data is encapsulated inside a message ({@link android.nfc.NdefMessage}) that contains one +or more records ({@link android.nfc.NdefRecord}). Each NDEF record must be well-formed according to +the specification of the type of record that you want to create. Android +also supports other types of tags that do not contain NDEF data, which you can work with by using +the classes in the {@link android.nfc.tech} package. To learn more +about these technologies, see the <a href="{@docRoot}guide/topics/nfc/advanced-nfc.html">Advanced +NFC</a> topic. Working with these other types of tags involves +writing your own protocol stack to communicate with the tags, so we recommend using NDEF when +possible for ease of development and maximum support for Android-powered devices. +</p> + +<p class="note"><strong>Note:</strong> +To download complete NDEF specifications, go to the <a +href="http://www.nfc-forum.org/specs/spec_license">NFC Forum Specification Download</a> site and see +<a href="#creating-records">Creating common types of NDEF records</a> for examples of how to +construct NDEF records. </p> + +<p>Now that you have some background in NFC tags, the following sections describe in more detail how +Android handles NDEF formatted tags. When an Android-powered device scans an NFC tag containing NDEF +formatted data, it parses the message and tries to figure out the data's MIME type or identifying +URI. To do this, the system reads the first {@link android.nfc.NdefRecord} inside the {@link +android.nfc.NdefMessage} to determine how to interpret the entire NDEF message (an NDEF message can +have multiple NDEF records). In a well-formed NDEF message, the first {@link android.nfc.NdefRecord} +contains the following fields: +<dl> + <dt><strong>3-bit TNF (Type Name Format)</strong></dt> + <dd>Indicates how to interpret the variable length type field. Valid values are described in +described in <a href="#table1">Table 1</a>.</dd> + + <dt><strong>Variable length type</strong></dt> + <dd>Describes the type of the record. If using {@link android.nfc.NdefRecord#TNF_WELL_KNOWN}, use +this field to specify the Record Type Definition (RTD). Valid RTD values are described in <a +href="#table2">Table 2</a>.</dd> + +<dt><strong>Variable length ID</strong></dt> +<dd>A unique identifier for the record. This field is not used often, but +if you need to uniquely identify a tag, you can create an ID for it.</dd> + +<dt><strong>Variable length payload</strong></dt> +<dd>The actual data payload that you want to read or write. An NDEF +message can contain multiple NDEF records, so don't assume the full payload is in the first NDEF +record of the NDEF message.</dd> + +</dl> + +<p>The tag dispatch system uses the TNF and type fields to try to map a MIME type or URI to the +NDEF message. If successful, it encapsulates that information inside of a {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent along with the actual payload. However, there +are cases when the tag dispatch system cannot determine the type of data based on the first NDEF +record. This happens when the NDEF data cannot be mapped to a MIME type or URI, or when the +NFC tag does not contain NDEF data to begin with. In such cases, a {@link +android.nfc.Tag} object that has information about the tag's technologies and the payload are +encapsulated inside of a {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent instead.</p> + +<p> +<a href="#table1">Table 1.</a> describes how the tag dispatch system maps TNF and type +fields to MIME types or URIs. It also describes which TNFs cannot be mapped to a MIME type or URI. +In these cases, the tag dispatch system falls back to +{@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}. + +<p>For example, if the tag dispatch system encounters a record of type {@link +android.nfc.NdefRecord#TNF_ABSOLUTE_URI}, it maps the variable length type field of that record +into a URI. The tag dispatch system encapsulates that URI in the data field of an {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent along with other information about the tag, +such as the payload. On the other hand, if it encounters a record of type {@link +android.nfc.NdefRecord#TNF_UNKNOWN}, it creates an intent that encapsulates the tag's technologies +instead.</p> + + +<p class="table-caption" id="table1"> + <strong>Table 1.</strong> Supported TNFs and their mappings</p> +<table id="mappings"> + <tr> + <th>Type Name Format (TNF)</th> + <th>Mapping</th> + </tr> + <tr> + <td>{@link android.nfc.NdefRecord#TNF_ABSOLUTE_URI}</td> + <td>URI based on the type field.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_EMPTY}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_EXTERNAL_TYPE}</td> + <td>URI based on the URN in the type field. The URN is encoded into the NDEF type field in + a shortened form: <code><em><domain_name>:<service_name></em></code>. + Android maps this to a URI in the form: + <code>vnd.android.nfc://ext/<em><domain_name>:<service_name></em></code>.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_MIME_MEDIA}</td> + <td>MIME type based on the type field.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_UNCHANGED}</td> + <td>Invalid in the first record, so falls back to + {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_UNKNOWN}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#TNF_WELL_KNOWN}</td> + <td>MIME type or URI depending on the Record Type Definition (RTD), which you set in the +type field. See <a href="#well_known">Table 2.</a> for more information on +available RTDs and their mappings.</td> + </tr> +</table> + +<p class="table-caption" id="table2"> + <strong>Table 2.</strong> Supported RTDs for TNF_WELL_KNOWN and their +mappings</p> +<table id="well-known"> + <tr> + <th>Record Type Definition (RTD)</th> + <th>Mapping</th> + </tr> + <tr> + <td>{@link android.nfc.NdefRecord#RTD_ALTERNATIVE_CARRIER}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_CARRIER}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_REQUEST}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_HANDOVER_SELECT}</td> + <td>Falls back to {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_SMART_POSTER}</td> + <td>URI based on parsing the payload.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_TEXT}</td> + <td>MIME type of <code>text/plain</code>.</td> + </tr> + <td>{@link android.nfc.NdefRecord#RTD_URI}</td> + <td>URI based on payload.</td> + </tr> +</table> + +<h3 id="dispatching">How NFC Tags are Dispatched to Applications</h3> + +<p>When the tag dispatch system is done creating an intent that encapsulates the NFC tag and its +identifying information, it sends the intent to an interested application that +filters for the intent. If more than one application can handle the intent, the Activity Chooser +is presented so the user can select the Activity. The tag dispatch system defines three intents, +which are listed in order of highest to lowest priority:</p> + +<ol> + <li> + {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED}: This intent is used to start an +Activity when a tag that contains an NDEF payload is scanned and is of a recognized type. This is +the highest priority intent, and the tag dispatch system tries to start an Activity with this +intent before any other intent, whenever possible. + </li> + + <li>{@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}: If no activities register to +handle the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} +intent, the tag dispatch system tries to start an application with this intent. This +intent is also directly started (without starting {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} first) if the tag that is scanned +contains NDEF data that cannot be mapped to a MIME type or URI, or if the tag does not contain NDEF +data but is of a known tag technology. +</li> + + <li>{@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}: This intent is started + if no activities handle the {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} + intents.</li> + </ol> + +<p>The basic way the tag dispatch system works is as follows:</p> + +<ol> + <li>Try to start an Activity with the intent that was created by the tag dispatch system +when parsing the NFC tag (either +{@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}).</li> + <li>If no activities filter for that intent, try to start an Activity with the next + lowest priority intent (either {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} or {@link +android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}) until an application filters for the + intent or until the tag dispatch system tries all possible intents.</li> + <li>If no applications filter for any of the intents, do nothing.</li> +</ol> + +<img src="{@docRoot}images/nfc_tag_dispatch.png" /> + +<p class="figure"><strong>Figure 1. </strong> Tag Dispatch System</p> + + +<p>Whenever possible, work with NDEF messages and the {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent, because it is the most specific out of +the three. This intent allows you to start your application at a more appropriate time than the +other two intents, giving the user a better experience.</p> + +<h2 id="manifest">Requesting NFC Access in the Android Manifest</h2> + + <p>Before you can access a device's NFC hardware and properly handle NFC intents, declare these + items in your <code>AndroidManifest.xml</code> file:</p> + + <ul> + <li>The NFC <code><uses-permission></code> element to access the NFC hardware: + <pre> +<uses-permission android:name="android.permission.NFC" /> +</pre> + </li> + + <li>The minimum SDK version that your application can support. API level 9 only supports + limited tag dispatch via {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}, and only gives + access to NDEF messages via the {@link android.nfc.NfcAdapter#EXTRA_NDEF_MESSAGES} extra. No + other tag properties or I/O operations are accessible. API level 10 + includes comprehensive reader/writer support as well as foreground NDEF pushing, and API level + 14 provides an easier way to push NDEF messages to other devices with Android Beam and extra + convenience methods to create NDEF records. +<pre class="pretty-print"> +<uses-sdk android:minSdkVersion="10"/> +</pre> + </li> + + <li>The <code>uses-feature</code> element so that your application shows up in the Android +Market only for devices that have NFC hardware: + <pre> +<uses-feature android:name="android.hardware.nfc" android:required="true" /> +</pre> +<p>If your application uses NFC functionality, but that functionality is not crucial to your +application, you can omit the <code>uses-feature</code> element and check for NFC avalailbility at +runtime by checking to see if {@link android.nfc.NfcAdapter#getDefaultAdapter getDefaultAdapter()} +is <code>null</code>.</p> + </li> + </ul> + + <h2 id="filtering-intents">Filtering for NFC Intents</h2> + + <p>To start your application when an NFC tag that you want to handle is scanned, your application +can filter for one, two, or all three of the NFC intents in the Android manifest. However, you +usually want to filter for the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intent for the +most control of when your application starts. The {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent is a fallback for {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} when no applications filter for + {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or for when the payload is not +NDEF. Filtering for {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} is usually too general of a +category to filter on. Many applications will filter for {@link +android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} before {@link +android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED}, so your application has a low probability of +starting. {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} is only available as a last resort +for applications to filter for in the cases where no other applications are installed to handle the +{@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} or {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED}intent.</p> + +<p>Because NFC tag deployments vary and are many times not under your control, this is not always +possible, which is why you can fallback to the other two intents when necessary. When you have +control over the types of tags and data written, it is recommended that you use NDEF to format your +tags. The following sections describe how to filter for each type of intent.</p> + + +<h3 id="ndef-disc">ACTION_NDEF_DISCOVERED</h3> +<p> +To filter for {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} intents, declare the +intent filter along with the type of data that you want to filter for. The +following example filters for {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} +intents with a MIME type of <code>text/plain</code>: +</p> +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED"/> + <category android:name="android.intent.category.DEFAULT"/> + <data android:mimeType="text/plain" /> +</intent-filter> +</pre> +<p>The following example filters for a URI in the form of +<code>http://developer.android.com/index.html</code>. +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED"/> + <category android:name="android.intent.category.DEFAULT"/> + <data android:scheme="http" + android:host="developer.android.com" + android:pathPrefix="/index.html" /> +</intent-filter> +</pre> + + + <h3 id="tech-disc">ACTION_TECH_DISCOVERED</h3> + + <p>If your activity filters for the {@link android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent, +you must create an XML resource file that specifies the technologies that your activity supports +within a <code>tech-list</code> set. Your activity is + considered a match if a <code>tech-list</code> set is a subset of the technologies that are + supported by the tag, which you can obtain by calling {@link android.nfc.Tag#getTechList + getTechList()}.</p> + + <p>For example, if the tag that is scanned supports MifareClassic, NdefFormatable, and NfcA, your + <code>tech-list</code> set must specify all three, two, or one of the technologies (and nothing + else) in order for your activity to be matched.</p> + + <p>The following sample defines all of the technologies. You can remove the ones that you do not + need. Save this file (you can name it anything you wish) in the + <code><project-root>/res/xml</code> folder.</p> + <pre> +<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> + <tech-list> + <tech>android.nfc.tech.IsoDep</tech> + <tech>android.nfc.tech.NfcA</tech> + <tech>android.nfc.tech.NfcB</tech> + <tech>android.nfc.tech.NfcF</tech> + <tech>android.nfc.tech.NfcV</tech> + <tech>android.nfc.tech.Ndef</tech> + <tech>android.nfc.tech.NdefFormatable</tech> + <tech>android.nfc.tech.MifareClassic</tech> + <tech>android.nfc.tech.MifareUltralight</tech> + </tech-list> +</resources> +</pre> + + <p>You can also specify multiple <code>tech-list</code> sets. Each of the <code>tech-list</code> + sets is considered independently, and your activity is considered a match if any single + <code>tech-list</code> set is a subset of the technologies that are returned by {@link + android.nfc.Tag#getTechList getTechList()}. This provides <code>AND</code> and <code>OR</code> + semantics for matching technologies. The following example matches tags that can support the + NfcA and Ndef technologies or can support the NfcB and Ndef technologies:</p> + <pre> +<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> + <tech-list> + <tech>android.nfc.tech.NfcA</tech> + <tech>android.nfc.tech.Ndef</tech> + </tech-list> +</resources> + +<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> + <tech-list> + <tech>android.nfc.tech.NfcB</tech> + <tech>android.nfc.tech.Ndef</tech> + </tech-list> +</resources> +</pre> + + <p>In your <code>AndroidManifest.xml</code> file, specify the resource file that you just created + in the <code><meta-data></code> element inside the <code><activity></code> + element like in the following example:</p> + <pre> +<activity> +... +<intent-filter> + <action android:name="android.nfc.action.TECH_DISCOVERED"/> +</intent-filter> + +<meta-data android:name="android.nfc.action.TECH_DISCOVERED" + android:resource="@xml/nfc_tech_filter" /> +... +</activity> +</pre> + +<p>For more information about working with tag technologies and the {@link +android.nfc.NfcAdapter#ACTION_TECH_DISCOVERED} intent, see <a +href="{@docRoot}guide/topics/nfc/advanced-nfc.html#tag-tech">Working with Supported Tag +Technologies</a> in the Advanced NFC document.</p> +<h3 id="tag-disc">ACTION_TAG_DISCOVERED</h3> +<p>To filter for {@link android.nfc.NfcAdapter#ACTION_TAG_DISCOVERED} use the following intent +filter:</p> + + +<pre><intent-filter> + <action android:name="android.nfc.action.TAG_DISCOVERED"/> +</intent-filter> +</pre> + + + +<h3 id="obtain-info">Obtaining information from intents</h3> + +<p>If an activity starts because of an NFC intent, you can obtain information about the scanned NFC +tag from the intent. Intents can contain the following extras depending on the tag that was scanned: + +<ul> + <li>{@link android.nfc.NfcAdapter#EXTRA_TAG} (required): A {@link android.nfc.Tag} object +representing the scanned tag.</li> + <li>{@link android.nfc.NfcAdapter#EXTRA_NDEF_MESSAGES} (optional): An array of NDEF messages +parsed from the tag. This extra is mandatory on {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED +intents.</li> + <li>{@link android.nfc.NfcAdapter#EXTRA_ID} (optional): The low-level ID of the tag.</li></ul> + +<p>To obtain these extras, check to see if your activity was launched with one of +the NFC intents to ensure that a tag was scanned, and then obtain the extras out of the +intent. The following example checks for the {@link android.nfc.NfcAdapter#ACTION_NDEF_DISCOVERED} +intent and gets the NDEF messages from an intent extra.</p> + +<pre> +public void onResume() { + super.onResume(); + ... + if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) { + Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES); + if (rawMsgs != null) { + msgs = new NdefMessage[rawMsgs.length]; + for (int i = 0; i < rawMsgs.length; i++) { + msgs[i] = (NdefMessage) rawMsgs[i]; + } + } + } + //process the msgs array +} +</pre> + +<p>Alternatively, you can obtain a {@link android.nfc.Tag} object from the intent, which will +contain the payload and allow you to enumerate the tag's technologies:</p> + +<pre>Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);</pre> + + +<h2 id="creating-records">Creating Common Types of NDEF Records</h2> +<p>This section describes how to create common types of NDEF records to help you when writing to +NFC tags or sending data with Android Beam. It also describes how to create the corresponding +intent filter for the record. All of these NDEF record examples should be in the first NDEF +record of the NDEF message that you are writing to a tag or beaming.</p> + +<h3 id="abs-uri">TNF_ABSOLUTE_URI</h3> +<p>Given the following {@link android.nfc.NdefRecord#TNF_ABSOLUTE_URI} NDEF record, which is +stored as the first record inside of an {@link android.nfc.NdefMessage}:</p> + +<pre> +NdefRecord uriRecord = new NdefRecord( + NdefRecord.TNF_ABSOLUTE_URI , + "http://developer.android.com/index.html".getBytes(Charset.forName("US-ASCII")), + new byte[0], new byte[0]); +</pre> + +<p>the intent filter would look like this:</p> +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED" /> + <category android:name="android.intent.category.DEFAULT" /> + <data android:scheme="http" + android:host="developer.android.com" + android:pathPrefix="/index.html" /> +</intent-filter> +</pre> + + +<h3 id="mime">TNF_MIME_MEDIA</h3> +<p>Given the following {@link android.nfc.NdefRecord#TNF_MIME_MEDIA} NDEF record, which is stored as +the first record inside +of an {@link android.nfc.NdefMessage}:</p> +<pre> +NdefRecord mimeRecord = new NdefRecord( + NdefRecord.TNF_MIME_MEDIA , + "application/com.example.android.beam".getBytes(Charset.forName("US-ASCII")), + new byte[0], "Beam me up, Android!".getBytes(Charset.forName("US-ASCII"))); +</pre> + +<p>the intent filter would look like this:</p> +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED" /> + <category android:name="android.intent.category.DEFAULT" /> + <data android:mimeType="application/com.example.android.beam" /> +</intent-filter> +</pre> + + +<h3 id="well-known-text">TNF_WELL_KNOWN with RTD_TEXT</h3> + +<p>Given the following {@link android.nfc.NdefRecord#TNF_WELL_KNOWN} NDEF record, which is stored as +the first record inside of an {@link android.nfc.NdefMessage}:</p> +<pre> +public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) { + byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII")); + Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16"); + byte[] textBytes = payload.getBytes(utfEncoding); + int utfBit = encodeInUtf8 ? 0 : (1 << 7); + char status = (char) (utfBit + langBytes.length); + byte[] data = new byte[1 + langBytes.length + textBytes.length]; + data[0] = (byte) status; + System.arraycopy(langBytes, 0, data, 1, langBytes.length); + System.arraycopy(textBytes, 0, data, 1 + langBytes.length, textBytes.length); + NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN, + NdefRecord.RTD_TEXT, new byte[0], data); + return record; +} +</pre> + +<p>the intent filter would look like this:</p> +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED" /> + <category android:name="android.intent.category.DEFAULT" /> + <data android:mimeType="text/plain" /> +</intent-filter> +</pre> + + +<h3 id="well-known-uri">TNF_WELL_KNOWN with RTD_URI</h3> + +<p>Given the following {@link android.nfc.NdefRecord#TNF_WELL_KNOWN} NDEF record, which is stored as +the first record inside of an {@link android.nfc.NdefMessage}:</p> + +<pre> +byte[] uriField = "example.com".getBytes(Charset.forName("US-ASCII")); +byte[] payload = new byte[uriField.length + 1]; //add 1 for the URI Prefix +byte payload[0] = 0x01; //prefixes http://www. to the URI +System.arraycopy(uriField, 0, payload, 1, uriField.length); //appends URI to payload +NdefRecord rtdUriRecord = new NdefRecord( + NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_URI, new byte[0], payload); +</pre> + +<p>the intent filter would look like this:</p> + +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED" /> + <category android:name="android.intent.category.DEFAULT" /> + <data android:scheme="http" + android:host="example.com" + android:pathPrefix="" /> +</intent-filter> +</pre> + +<h3 id="ext-type">TNF_EXTERNAL_TYPE</h3> +<p>Given the following {@link android.nfc.NdefRecord#TNF_EXTERNAL_TYPE} NDEF record, which is stored +as the first record inside of an {@link android.nfc.NdefMessage}:</p> + +<pre> +byte[] payload; +... +NdefRecord mimeRecord = new NdefRecord( + NdefRecord.TNF_EXTERNAL_TYPE, "example.com:externalType", new byte[0], payload); +</pre> + +<p>the intent filter would look like this:</p> +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED" /> + <category android:name="android.intent.category.DEFAULT" /> + <data android:scheme="vnd.android.nfc" + android:host="ext" + android:pathPrefix="/example.com:externalType"/> +</intent-filter> +</pre> + + +<p>Use TNF_EXTERNAL_TYPE for more generic NFC tag deployments to better support both +Android-powered and non-Android-powered devices.</p> + +<p class="note"><strong>Note</strong>: URNs for {@link +android.nfc.NdefRecord#TNF_EXTERNAL_TYPE} have a canonical format of: +<code>urn:nfc:ext:example.com:externalType</code>, however the NFC Forum RTD specification +declares that the <code>urn:nfc:ext:</code> portion of the URN must be ommitted from the +NDEF record. So all you need to provide is the domain (<code>example.com</code> in the example) +and type (<code>externalType</code> in the example) separated by a colon. +When dispatching TNF_EXTERNAL_TYPE, Android converts the <code>urn:nfc:ext:example.com:externalType</code> URN to a +<code>vnd.android.nfc://ext/example.com:externalType</code> URI, which is what the intent filter in the example +declares.</p> + +<h3 id="aar">Android Application Records</h3> + +<p> +Introduced in Android 4.0 (API level 14), an Android Application Record (AAR) provides a stronger +certainty that your application is started when an NFC tag is scanned. An AAR has the package name +of an application embedded inside an NDEF record. You can add an AAR to any NDEF record of your NDEF message, +because Android searches the entire NDEF message for AARs. If it finds an AAR, it starts the application based +on the package name inside the AAR. If the application is not present on the device, +Android Market is launched to download the application.</p> + +<p>AARs are useful if you want to prevent other applications from filtering for the same intent and +potentially handling specific tags that you have deployed. AARs are only supported at the +application level, because of the package name constraint, and not at the Activity level as with +intent filtering. If you want to handle an intent at the Activity level, <a +href="filtering-intents">use intent filters</a>. +</p> + + + +<p>If a tag contains an AAR, the tag dispatch system dispatches in the following manner:</p> +<ol> + <li>Try to start an Activity using an intent filter as normal. If the Activity that matches +the intent also matches the AAR, start the Activity.</li> + <li>If the Activity that filters for the intent does not match the +AAR, if multiple Activities can handle the intent, or if no Activity handles the intent, start the +application specified by the AAR.</li> + <li>If no application can start with the AAR, go to the Android Market to download the +application based on the AAR.</li> +</ol> + +</p> + +<p class="note"><strong>Note:</strong> You can override AARs and the intent dispatch system with the <a +href="{@docRoot}guide/topics/nfc/advanced-nfc.html#foreground-dispatch">foreground dispatch +system</a>, which allows a foreground activity to have priority when an NFC tag is discovered. +With this method, the activity must be in the foreground to +override AARs and the intent dispatch system.</p> + +<p>If you still want to filter for scanned tags that do not contain an AAR, you can declare +intent filters as normal. This is useful if your application is interested in other tags +that do not contain an AAR. For example, maybe you want to guarantee that your application handles +proprietary tags that you deploy as well as general tags deployed by third parties. Keep in mind +that AARs are specific to Android 4.0 devices or later, so when deploying tags, you most likely want +to use a combination of AARs and MIME types/URIs to support the widest range of devices. In +addition, when you deploy NFC tags, think about how you want to write your NFC tags to enable +support for the most devices (Android-powered and other devices). You can do this by +defining a relatively unique MIME type or URI to make it easier for applications to distinguish. +</p> + +<p>Android provides a simple API to create an AAR, +{@link android.nfc.NdefRecord#createApplicationRecord createApplicationRecord()}. All you need to +do is embed the AAR anywhere in your {@link android.nfc.NdefMessage}. You do not want +to use the first record of your {@link android.nfc.NdefMessage}, unless the AAR is the only +record in the {@link android.nfc.NdefMessage}. This is because the Android +system checks the first record of an {@link android.nfc.NdefMessage} to determine the MIME type or +URI of the tag, which is used to create an intent for applications to filter. The following code +shows you how to create an AAR:</p> + +<pre> +NdefMessage msg = new NdefMessage( + new NdefRecord[] { + ..., + NdefRecord.createApplicationRecord("com.example.android.beam")} +</pre> + + +<h2 id="p2p">Beaming NDEF Messages to Other Devices</h2> + +<p>Android Beam allows simple peer-to-peer data exchange between two Android-powered devices. The +application that wants to beam data to another device must be in the foreground and the device +receiving the data must not be locked. When the beaming device comes in close enough contact with a +receiving device, the beaming device displays the "Touch to Beam" UI. The user can then choose +whether or not to beam the message to the receiving device.</p> + +<p class="note"><strong>Note:</strong> Foreground NDEF pushing was available at API level 10, +which provides similar functionality to Android Beam. These APIs have since been deprecated, but +are available to support older devices. See {@link android.nfc.NfcAdapter#enableForegroundNdefPush +enableForegroundNdefPush()} for more information.</p> + +<p>You can enable Android Beam for your application by calling one of the two methods:</p> + <ul> + <li>{@link android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()}: Accepts an +{@link android.nfc.NdefMessage} to set as the message to beam. Automatically beams the message +when two devices are in close enough proximity.</li> + <li>{@link android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback()}: +Accepts a callback that contains a +{@link android.nfc.NfcAdapter.CreateNdefMessageCallback#createNdefMessage createNdefMessage()} +which is called when a device is in range to beam data to. The callback lets you create +the NDEF message only when necessary.</li> + </ul> + +<p>An activity can only push one NDEF message at a time, so {@link +android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback()} takes precedence +over {@link android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} if both are set. To use +Android Beam, the following general guidelines must be met: +</p> + + <ul> + <li>The activity that is beaming the data must be in the foreground. Both devices must have +their screens unlocked.</li> + + <li>You must encapsulate the data that you are beaming in an {@link android.nfc.NdefMessage} + object.</li> + + <li>The NFC device that is receiving the beamed data must support the + <code>com.android.npp</code> NDEF push protocol or NFC Forum's SNEP (Simple NDEF Exchange +Protocol). The <code>com.android.npp</code> protocol is required for devices on API level 9 (Android +2.3) to API level 13 (Android 3.2). <code>com.android.npp</code> and SNEP are both required on +API level 14 (Android 4.0) and later.</li> +</li> + </ul> + + <p class="note"><strong>Note:</strong> If your activity enables Android Beam and is +in the foreground, the standard intent dispatch system is disabled. However, if your activity also +enables <a href="{@docRoot}guide/topics/nfc/advanced-nfc.html#foreground-dispatch">foreground +dispatching</a>, then it can still scan tags that match the intent filters set in the foreground +dispatching.</p> + + <p>To enable Android Beam:</p> + + <ol> + <li>Create an {@link android.nfc.NdefMessage} that contains the {@link android.nfc.NdefRecord}s +that you want to push onto the other device.</li> + + <li>Call {@link +android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} with a {@link +android.nfc.NdefMessage} or call {@link +android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback} passing in a {@link +android.nfc.NfcAdapter.CreateNdefMessageCallback} object in the <code>onCreate()</code> method of +your activity. These methods require at least one activity that you want to enable with Android +Beam, along with an optional list of other activities to activate. + +<p>In general, you normally use {@link +android.nfc.NfcAdapter#setNdefPushMessage setNdefPushMessage()} if your Activity only needs to +push the same NDEF message at all times, when two devices are in range to communicate. You use +{@link android.nfc.NfcAdapter#setNdefPushMessageCallback setNdefPushMessageCallback} when your +application cares about the current context of the application and wants to push an NDEF message +depending on what the user is doing in your application.</p> + </li> + </ol> + +<p>The following sample shows how a simple activity calls {@link +android.nfc.NfcAdapter.CreateNdefMessageCallback} in the <code>onCreate()</code> method of an +activity (see <a href="{@docRoot}resources/samples/AndroidBeam/index.html"></a> for the +complete sample). This example also has methods to help you create a MIME record:</p> + +<pre id="code-example"> +package com.example.android.beam; + +import android.app.Activity; +import android.content.Intent; +import android.nfc.NdefMessage; +import android.nfc.NdefRecord; +import android.nfc.NfcAdapter; +import android.nfc.NfcAdapter.CreateNdefMessageCallback; +import android.nfc.NfcEvent; +import android.os.Bundle; +import android.os.Parcelable; +import android.widget.TextView; +import android.widget.Toast; +import java.nio.charset.Charset; + + +public class Beam extends Activity implements CreateNdefMessageCallback { + NfcAdapter mNfcAdapter; + TextView textView; + + @Override + public void onCreate(Bundle savedInstanceState) { + super.onCreate(savedInstanceState); + setContentView(R.layout.main); + TextView textView = (TextView) findViewById(R.id.textView); + // Check for available NFC Adapter + mNfcAdapter = NfcAdapter.getDefaultAdapter(this); + if (mNfcAdapter == null) { + Toast.makeText(this, "NFC is not available", Toast.LENGTH_LONG).show(); + finish(); + return; + } + // Register callback + mNfcAdapter.setNdefPushMessageCallback(this, this); + } + + @Override + public NdefMessage createNdefMessage(NfcEvent event) { + String text = ("Beam me up, Android!\n\n" + + "Beam Time: " + System.currentTimeMillis()); + NdefMessage msg = new NdefMessage( + new NdefRecord[] { createMimeRecord( + "application/com.example.android.beam", text.getBytes()) + /** + * The Android Application Record (AAR) is commented out. When a device + * receives a push with an AAR in it, the application specified in the AAR + * is guaranteed to run. The AAR overrides the tag dispatch system. + * You can add it back in to guarantee that this + * activity starts when receiving a beamed message. For now, this code + * uses the tag dispatch system. + */ + //,NdefRecord.createApplicationRecord("com.example.android.beam") + }); + return msg; + } + + @Override + public void onResume() { + super.onResume(); + // Check to see that the Activity started due to an Android Beam + if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) { + processIntent(getIntent()); + } + } + + @Override + public void onNewIntent(Intent intent) { + // onResume gets called after this to handle the intent + setIntent(intent); + } + + /** + * Parses the NDEF Message from the intent and prints to the TextView + */ + void processIntent(Intent intent) { + textView = (TextView) findViewById(R.id.textView); + Parcelable[] rawMsgs = intent.getParcelableArrayExtra( + NfcAdapter.EXTRA_NDEF_MESSAGES); + // only one message sent during the beam + NdefMessage msg = (NdefMessage) rawMsgs[0]; + // record 0 contains the MIME type, record 1 is the AAR, if present + textView.setText(new String(msg.getRecords()[0].getPayload())); + } + + /** + * Creates a custom MIME type encapsulated in an NDEF record + */ + public NdefRecord createMimeRecord(String mimeType, byte[] payload) { + byte[] mimeBytes = mimeType.getBytes(Charset.forName("US-ASCII")); + NdefRecord mimeRecord = new NdefRecord( + NdefRecord.TNF_MIME_MEDIA, mimeBytes, new byte[0], payload); + return mimeRecord; + } +} +</pre> + +<p>Note that this code comments out an AAR, which you can remove. If you enable the AAR, the +application specified in the AAR always receives the Android Beam message. If the application is not +present, the Android Market is started to download the application. Therefore, the following intent +filter is not technically necessary for Android 4.0 devices or later if the AAR is used: +</p> + +<pre> +<intent-filter> + <action android:name="android.nfc.action.NDEF_DISCOVERED"/> + <category android:name="android.intent.category.DEFAULT"/> + <data android:mimeType="application/com.example.android.beam"/> +</intent-filter> +</pre> +<p>With this intent filter, the <code>com.example.android.beam</code> application now can be started +when it scans an NFC tag or receives an Android Beam with an AAR of +type <code>com.example.android.beam</code>, or when an NDEF formatted message contains a MIME record +of type <code>application/com.example.android.beam</code>.</p> + +<p>Even though AARs guarantee an application is started or downloaded, intent filters are +recommended, because they let you start an Activity of your choice in your +application instead of always starting the main Activity within the package specified by an AAR. +AARs do not have Activity level granularity. Also, because some Android-powered devices do not +support AARs, you should also embed identifying information in the first NDEF record of your NDEF +messages and filter for that as well, just in case. See <a href="#creating-records">Creating Common +Types of NDEF records</a> for more information on how to create records. +</p> diff --git a/docs/html/images/nfc_tag_dispatch.png b/docs/html/images/nfc_tag_dispatch.png Binary files differnew file mode 100644 index 0000000..70ed711 --- /dev/null +++ b/docs/html/images/nfc_tag_dispatch.png |
