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diff --git a/docs/html/guide/topics/nfc/nfc.jd b/docs/html/guide/topics/nfc/nfc.jd new file mode 100644 index 0000000..175bc7c --- /dev/null +++ b/docs/html/guide/topics/nfc/nfc.jd @@ -0,0 +1,923 @@ +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="#manifest">Requesting NFC Access in the Android Manifest</a></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> |