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Diffstat (limited to 'docs/html/training/basics/firstapp/starting-activity.jd')
| -rw-r--r-- | docs/html/training/basics/firstapp/starting-activity.jd | 159 |
1 files changed, 114 insertions, 45 deletions
diff --git a/docs/html/training/basics/firstapp/starting-activity.jd b/docs/html/training/basics/firstapp/starting-activity.jd index 3dafcfa..8943c9d 100644 --- a/docs/html/training/basics/firstapp/starting-activity.jd +++ b/docs/html/training/basics/firstapp/starting-activity.jd @@ -19,11 +19,7 @@ previous.link=building-ui.html <li><a href="#RespondToButton">Respond to the Send Button</a></li> <li><a href="#BuildIntent">Build an Intent</a></li> <li><a href="#StartActivity">Start the Second Activity</a></li> - <li><a href="#CreateActivity">Create the Second Activity</a> - <ol> - <li><a href="#AddToManifest">Add it to the manifest</a></li> - </ol> - </li> + <li><a href="#CreateActivity">Create the Second Activity</a></li> <li><a href="#ReceiveIntent">Receive the Intent</a></li> <li><a href="#DisplayMessage">Display the Message</a></li> </ol> @@ -49,8 +45,8 @@ starts a new activity when the user clicks the Send button.</p> <h2 id="RespondToButton">Respond to the Send Button</h2> -<p>To respond to the button's on-click event, open the <code>main.xml</code> layout file and add the -<a +<p>To respond to the button's on-click event, open the <code>activity_main.xml</code> +layout file and add the <a href="{@docRoot}reference/android/view/View.html#attr_android:onClick">{@code android:onClick}</a> attribute to the {@link android.widget.Button <Button>} element:</p> @@ -67,7 +63,8 @@ href="{@docRoot}reference/android/view/View.html#attr_android:onClick">{@code android:onClick}</a> attribute’s value, <code>"sendMessage"</code>, is the name of a method in your activity that the system calls when the user clicks the button.</p> -<p>Open the <code>MainActivity</code> class and add the corresponding method:</p> +<p>Open the <code>MainActivity</code> class (located in the project's +<code>src/</code> directory) and add the corresponding method:</p> <pre> /** Called when the user clicks the Send button */ @@ -76,6 +73,11 @@ public void sendMessage(View view) { } </pre> +<p>This requires that you import the {@link android.view.View} class:</p> +<pre> +import android.view.View; +</pre> + <p class="note"><strong>Tip:</strong> In Eclipse, press Ctrl + Shift + O to import missing classes (Cmd + Shift + O on Mac).</p> @@ -137,7 +139,8 @@ will raise an error if you’re using an IDE such as Eclipse because the class d Ignore the error for now; you’ll create the class soon.</p> <p>An intent not only allows you to start another activity, but it can carry a bundle of data to the -activity as well. So, use {@link android.app.Activity#findViewById findViewById()} to get the +activity as well. Inside the {@code sendMessage()} method, +use {@link android.app.Activity#findViewById findViewById()} to get the {@link android.widget.EditText} element and add its text value to the intent:</p> <pre> @@ -147,11 +150,17 @@ String message = editText.getText().toString(); intent.putExtra(EXTRA_MESSAGE, message); </pre> +<p class="note"><strong>Note:</strong> +You now need import statements for <code>android.content.Intent</code> +and <code>android.widget.EditText</code>. You'll define the <code>EXTRA_MESSAGE</code> +constant in a moment.</p> + <p>An {@link android.content.Intent} can carry a collection of various data types as key-value pairs called <em>extras</em>. The {@link android.content.Intent#putExtra putExtra()} method takes the key name in the first parameter and the value in the second parameter.</p> -<p>In order for the next activity to query the extra data, you should define your key using a +<p>In order for the next activity to query the extra data, you should define the key +for your intent's extra using a public constant. So add the {@code EXTRA_MESSAGE} definition to the top of the {@code MainActivity} class:</p> @@ -166,9 +175,11 @@ public class MainActivity extends Activity { as a prefix. This ensures they are unique, in case your app interacts with other apps.</p> + + <h2 id="StartActivity">Start the Second Activity</h2> -<p>To start an activity, you simply need to call {@link android.app.Activity#startActivity +<p>To start an activity, call {@link android.app.Activity#startActivity startActivity()} and pass it your {@link android.content.Intent}. The system receives this call and starts an instance of the {@link android.app.Activity} specified by the {@link android.content.Intent}.</p> @@ -202,19 +213,19 @@ work.</p> <p>To create a new activity using Eclipse:</p> <ol> - <li>Click New <img src="{@docRoot}images/tools/eclipse-new.png" + <li>Click <strong>New</strong> <img src="{@docRoot}images/tools/eclipse-new.png" style="vertical-align:baseline;margin:0" /> in the toolbar.</li> <li>In the window that appears, open the <strong>Android</strong> folder and select <strong>Android Activity</strong>. Click <strong>Next</strong>.</li> <li>Select <strong>BlankActivity</strong> and click <strong>Next</strong>.</li> <li>Fill in the activity details: <ul> - <li><em>Project</em>: MyFirstApp</li> - <li><em>Activity Name</em>: DisplayMessageActivity</li> - <li><em>Layout Name</em>: activity_display_message</li> - <li><em>Navigation Type</em>: None</li> - <li><em>Hierarchial Parent</em>: com.example.myfirstapp.MainActivity</li> - <li><em>Title</em>: My Message</li> + <li><strong>Project</strong>: MyFirstApp</li> + <li><strong>Activity Name</strong>: DisplayMessageActivity</li> + <li><strong>Layout Name</strong>: activity_display_message</li> + <li><strong>Title</strong>: My Message</li> + <li><strong>Hierarchial Parent</strong>: com.example.myfirstapp.MainActivity</li> + <li><strong>Navigation Type</strong>: None</li> </ul> <p>Click <strong>Finish</strong>.</p> </li> @@ -224,44 +235,94 @@ work.</p> {@code DisplayMessageActivity.java} in the project's <code>src/</code> directory, next to the original {@code MainActivity.java} file.</p> -<p>Open the {@code DisplayMessageActivity.java} file. If you used Eclipse to create it, the class +<p>Open the {@code DisplayMessageActivity.java} file. If you used Eclipse to create this +activity:</p> +<ul> + <li>The class already includes an implementation of the required {@link android.app.Activity#onCreate onCreate()} -method. There's also an implementation of the {@link android.app.Activity#onCreateOptionsMenu +method.</li> + <li>There's also an implementation of the {@link android.app.Activity#onCreateOptionsMenu onCreateOptionsMenu()} method, but -you won't need it for this app so you can remove it. The class should look like this:</p> +you won't need it for this app so you can remove it.</li> + <li>There's also an implementation of {@link android.app.Activity#onOptionsItemSelected + onOptionsItemSelected()} which handles the behavior for the action bar's <em>Up</em> behavior. + Keep this one the way it is.</li> +</ul> + +<p>The class should look like this:</p> <pre> public class DisplayMessageActivity extends Activity { @Override - public void onCreate(Bundle savedInstanceState) { + protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_display_message); + // Show the Up button in the action bar. + getActionBar().setDisplayHomeAsUpEnabled(true); + } + + @Override + public boolean onOptionsItemSelected(MenuItem item) { + switch (item.getItemId()) { + case android.R.id.home: + NavUtils.navigateUpFromSameTask(this); + return true; + } + return super.onOptionsItemSelected(item); } } </pre> +<p>If you used an IDE other than Eclipse, update your {@code DisplayMessageActivity} +class with the above code.</p> + <p>All subclasses of {@link android.app.Activity} must implement the {@link android.app.Activity#onCreate onCreate()} method. The system calls this when creating a new -instance of the activity. It is where you must define the activity layout and where you should +instance of the activity. This method is where you must define the activity layout +with the {@link android.app.Activity#setContentView setContentView()} method +and is where you should perform initial setup for the activity components.</p> +<p class="note"><strong>Note:</strong> If you are using an IDE other than Eclipse, your project +does not contain the {@code activity_display_message} layout that's requested by +{@link android.app.Activity#setContentView setContentView()}. That's OK because +you will update this method later and won't be using that layout.</p> + + +<h3 id="AddTitle">Add the title string</h3> + +<p>If you used Eclipse, you can skip to the <a href="#AddToManifest">next section</a>, +because the template provides +the title string for the new activity.</p> + +<p>If you're using an IDE other than Eclipse, +add the new activity's title to the {@code strings.xml} file:</p> +<pre> +<resources> + ... + <string name="title_activity_display_message">My Message</string> +</resources> +</pre> + <h3 id="AddToManifest">Add it to the manifest</h3> -<p>You must declare all activities in your manifest file, <code>AndroidManifest.xml</code>, using an +<p>All activities must be declared in your manifest file, <code>AndroidManifest.xml</code>, using an <a href="{@docRoot}guide/topics/manifest/activity-element.html">{@code <activity>}</a> element.</p> -<p>When you use the Eclipse tools to create the activity, it creates a default entry. It should +<p>When you use the Eclipse tools to create the activity, it creates a default entry. If you're +using a different IDE, you need to add the manifest entry yourself. It should look like this:</p> <pre> <application ... > ... <activity - android:name=".DisplayMessageActivity" - android:label="@string/title_activity_display_message" > + android:name="com.example.myfirstapp.DisplayMessageActivity" + android:label="@string/title_activity_display_message" + android:parentActivityName="com.example.myfirstapp.MainActivity" > <meta-data android:name="android.support.PARENT_ACTIVITY" android:value="com.example.myfirstapp.MainActivity" /> @@ -269,24 +330,32 @@ look like this:</p> </application> </pre> -<p>The <a href="{@docRoot}guide/topics/manifest/meta-data-element.html">{@code - <meta-data>}</a> element declares the name of this activity's parent activity - within the app's logical hierarchy. The Android <a -href="{@docRoot}tools/extras/support-library.html">Support Library</a> uses this information - to implement default navigation behaviors, such as <a - href="{@docRoot}design/patterns/navigation.html">Up navigation</a>.</p> - -<p class="note"><strong>Note:</strong> During <a -href="{@docRoot}sdk/installing/adding-packages.html">installation</a>, you should have downloaded -the latest Support Library. Eclipse automatically includes this library in your app project (you -can see the library's JAR file listed under <em>Android Dependencies</em>). If you're not using -Eclipse, you may need to manually add the library to your project—follow this guide for <a -href="{@docRoot}tools/extras/support-library.html#SettingUp">setting up the Support Library</a>.</p> - -<p>The app is now runnable because the {@link android.content.Intent} in the -first activity now resolves to the {@code DisplayMessageActivity} class. If you run the app now, -clicking the Send button starts the second activity, but it's still using the default -"Hello world" layout.</p> +<p>The <a href="{@docRoot}guide/topics/manifest/activity-element.html#parent">{@code +android:parentActivityName}</a> attribute declares the name of this activity's parent activity +within the app's logical hierarchy. The system uses this value +to implement default navigation behaviors, such as <a +href="{@docRoot}design/patterns/navigation.html">Up navigation</a> on +Android 4.1 (API level 16) and higher. You can provide the same navigation behaviors for +older versions of Android by using the +<a href="{@docRoot}tools/extras/support-library.html">Support Library</a> and adding +the <a href="{@docRoot}guide/topics/manifest/meta-data-element.html">{@code +<meta-data>}</a> element as shown here.</p> + +<p class="note"><strong>Note:</strong> Your Android SDK should already include +the latest Android Support Library. It's included with the ADT Bundle but if you're using +a different IDE, you should have installed it during the +<a href="{@docRoot}sdk/installing/adding-packages.html">Adding Platforms and Packages</a> step. +When using the templates in Eclipse, the Support Library is automatically added to your app project +(you can see the library's JAR file listed under <em>Android Dependencies</em>). If you're not using +Eclipse, you need to manually add the library to your project—follow the guide for <a +href="{@docRoot}tools/extras/support-library.html#SettingUp">setting up the Support Library</a> +then return here.</p> + +<p>If you're developing with Eclipse, you can run the app now, but not much happens. +Clicking the Send button starts the second activity but it uses +a default "Hello world" layout provided by the template. You'll soon update the +activity to instead display a custom text view, so if you're using a different IDE, +don't worry that the app won't yet compile.</p> <h2 id="ReceiveIntent">Receive the Intent</h2> |