docs: add 101 class about intents, Interacting with Other Apps

page.title=Allowing Other Apps to Start Your Activity

parent.title=Interacting with Other Apps

parent.link=index.html

trainingnavtop=true

previous.title=Getting a Result from an Activity

previous.link=result.html

@jd:body

<div id="tb-wrapper">

  <div id="tb">

<h2>This lesson teaches you to</h2>

<ol>

  <li><a href="#AddIntentFilter">Add an Intent Filter</a></li>

  <li><a href="#HandleIntent">Handle the Intent in Your Activity</a></li>

  <li><a href="#ReturnResult">Return a Result</a></li>

</ol>

<h2>You should also read</h2>

<ul>

  <li><a href="{@docRoot}training/sharing/index.html">Sharing Content</a></li>

</ul>

  </div>

</div>

<p>The previous two lessons focused on one side of the story: starting another app's activity from

your app. But if your app can perform an action that might be useful to another app,

your app should be prepared to respond to action requests from other apps. For instance, if you

build a social app that can share messages or photos with the user's friends, it's in your best

interest to support the {@link android.content.Intent#ACTION_SEND} intent so users can initiate a

"share" action from another app and launch your app to perform the action.</p>

<p>To allow other apps to start your activity, you need to add an <a

href="{@docRoot}guide/topics/manifest/intent-filter-element.html">{@code &lt;intent-filter>}</a>

element in your manifest file for the corresponding <a

href="{@docRoot}guide/topics/manifest/activity-element.html">{@code &lt;activity>}</a> element.</p>

<p>When your app is installed on a device, the system identifies your intent

filters and adds the information to an internal catalog of intents supported by all installed apps.

When an app calls {@link android.app.Activity#startActivity

startActivity()} or {@link android.app.Activity#startActivityForResult startActivityForResult()},

with an implicit intent, the system finds which activity (or activities) can respond to the

intent.</p>

<h2 id="AddIntentFilter">Add an Intent Filter</h2>

<p>In order to properly define which intents your activity can handle, each intent filter you add

should be as specific as possible in terms of the type of action and data the activity

accepts.</p>

<p>The system may send a given {@link android.content.Intent} to an activity if that activity has

an intent filter fulfills the following criteria of the {@link android.content.Intent} object:</p>

<dl>

  <dt>Action</dt>

    <dd>A string naming the action to perform. Usually one of the platform-defined values such

as {@link android.content.Intent#ACTION_SEND} or {@link android.content.Intent#ACTION_VIEW}.

    <p>Specify this in your intent filter with the <a

href="{@docRoot}guide/topics/manifest/action-element.html">{@code &lt;action>}</a> element.

The value you specify in this element must be the full string name for the action, instead of the

API constant (see the examples below).</p></dd>

  <dt>Data</dt>

    <dd>A description of the data associated with the intent.

    <p>Specify this in your intent filter with the <a

href="{@docRoot}guide/topics/manifest/data-element.html">{@code &lt;data>}</a> element. Using one

or more attributes in this element, you can specify just the MIME type, just a URI prefix,

just a URI scheme, or a combination of these and others that indicate the data type

accepted.</p>

    <p class="note"><strong>Note:</strong> If you don't need to declare specifics about the data

{@link android.net.Uri} (such as when your activity handles to other kind of "extra" data, instead

of a URI), you should specify only the {@code android:mimeType} attribute to declare the type of

data your activity handles, such as {@code text/plain} or {@code image/jpeg}.</p>

</dd>

  <dt>Category</dt>

    <dd>Provides an additional way to characterize the activity handling the intent, usually related

to the user gesture or location from which it's started. There are several different categories

supported by the system, but most are rarely used. However, all implicit intents are defined with

{@link android.content.Intent#CATEGORY_DEFAULT} by default.

    <p>Specify this in your intent filter with the <a

href="{@docRoot}guide/topics/manifest/category-element.html">{@code &lt;category>}</a>

element.</p></dd>

</dl>

<p>In your intent filter, you can declare which criteria your activity accepts

by declaring each of them with corresponding XML elements nested in the <a

href="{@docRoot}guide/topics/manifest/intent-filter-element.html">{@code &lt;intent-filter>}</a>

element.</p>

<p>For example, here's an activity with an intent filter that handles the {@link

android.content.Intent#ACTION_SEND} intent when the data type is either text or an image:</p>

<pre>

<activity android:name="ShareActivity">

    <intent-filter>

        <action android:name="android.intent.action.SEND"/>

        <category android:name="android.intent.category.DEFAULT"/>

        <data android:mimeType="text/plain"/>

        <data android:mimeType="image/*"/>

    </intent-filter>

</activity>

</pre>

<p>Each incoming intent specifies only one action and one data type, but it's OK to declare multiple

instances of the <a href="{@docRoot}guide/topics/manifest/action-element.html">{@code

&lt;action>}</a>, <a href="{@docRoot}guide/topics/manifest/category-element.html">{@code

&lt;category>}</a>, and <a href="{@docRoot}guide/topics/manifest/data-element.html">{@code

&lt;data>}</a> elements in each

<a href="{@docRoot}guide/topics/manifest/intent-filter-element.html">{@code

&lt;intent-filter>}</a>.</p>

<p>If any two pairs of action and data are mutually exclusive in

their behaviors, you should create separate intent filters to specify which actions are acceptable

when paired with which data types.</p>

<p>For example, suppose your activity handles both text and images for both the {@link

android.content.Intent#ACTION_SEND} and {@link

android.content.Intent#ACTION_SENDTO} intents. In this case, you must define two separate

intent filters for the two actions because a {@link

android.content.Intent#ACTION_SENDTO} intent must use the data {@link android.net.Uri} to specify

the recipient's address using the {@code send} or {@code sendto} URI scheme. For example:</p>

<pre>

<activity android:name="ShareActivity">

    <!-- filter for sending text; accepts SENDTO action with sms URI schemes -->

    <intent-filter>

        <action android:name="android.intent.action.SENDTO"/>

        <category android:name="android.intent.category.DEFAULT"/>

        <data android:scheme="sms" />

        <data android:scheme="smsto" />

    </intent-filter>

    <!-- filter for sending text or images; accepts SEND action and text or image data -->

    <intent-filter>

        <action android:name="android.intent.action.SEND"/>

        <category android:name="android.intent.category.DEFAULT"/>

        <data android:mimeType="image/*"/>

        <data android:mimeType="text/plain"/>

    </intent-filter>

</activity>

</pre>

<p class="note"><strong>Note:</strong> In order to receive implicit intents, you must include the

{@link android.content.Intent#CATEGORY_DEFAULT} category in the intent filter. The methods {@link

android.app.Activity#startActivity startActivity()} and {@link

android.app.Activity#startActivityForResult startActivityForResult()} treat all intents as if they

contained the {@link android.content.Intent#CATEGORY_DEFAULT} category. If you do not declare it, no

implicit intents will resolve to your activity.</p>

<p>For more information about sending and receiving {@link android.content.Intent#ACTION_SEND}

intents that perform social sharing behaviors, see the lesson about <a

href="{@docRoot}training/sharing/receive.html">Receiving Content from Other Apps</a>.</p>

<h2 id="HandleIntent">Handle the Intent in Your Activity</h2>

<p>In order to decide what action to take in your activity, you can read the {@link

android.content.Intent} that was used to start it.</p>

<p>As your activity starts, call {@link android.app.Activity#getIntent()} to retrieve the

{@link android.content.Intent} that started the activity. You can do so at any time during the

lifecycle of the activity, but you should generally do so during early callbacks such as

{@link android.app.Activity#onCreate onCreate()} or {@link android.app.Activity#onStart()}.</p>

<p>For example:</p>

<pre>

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    // Get the intent that started this activity

    Intent intent = getIntent();

    Uri data = intent.getData();

    // Figure out what to do based on the intent type

    if (intent.getType().indexOf("image/") != -1) {

        // Handle intents with image data ...

    } else if (intent.getType().equals("text/plain")) {

        // Handle intents with text ...

    }

}

</pre>

<h2 id="ReturnResult">Return a Result</h2>

<p>If you want to return a result to the activity that invoked yours, simply call {@link

android.app.Activity#setResult(int,Intent) setResult()} to specify the result code and result {@link

android.content.Intent}. When your operation is done and the user should return to the original

activity, call {@link android.app.Activity#finish()} to close (and destroy) your activity. For

example:</p>

<pre>

// Create intent to deliver some kind of result data

Intent result = new Intent("com.example.RESULT_ACTION", Uri.parse("content://result_uri");

setResult(Activity.RESULT_OK, result);

finish();

</pre>

<p>You must always specify a result code with the result. Generally, it's either {@link

android.app.Activity#RESULT_OK} or {@link android.app.Activity#RESULT_CANCELED}. You can then

provide additional data with an {@link android.content.Intent}, as necessary.</p>

<p class="note"><strong>Note:</strong> The result is set to {@link

android.app.Activity#RESULT_CANCELED} by default. So, if the user presses the <em>Back</em>

button before completing the action and before you set the result, the original activity receives

the "canceled" result.</p>

<p>If you simply need to return an integer that indicates one of several result options, you can set

the result code to any value higher than 0. If you use the result code to deliver an integer and you

have no need to include the {@link android.content.Intent}, you can call {@link

android.app.Activity#setResult(int) setResult()} and pass only a result code. For example:</p>

<pre>

setResult(RESULT_COLOR_RED);

finish();

</pre>

<p>In this case, there might be only a handful of possible results, so the result code is a locally

defined integer (greater than 0). This works well when you're returning a result to an activity

in your own app, because the activity that receives the result can reference the public

constant to determine the value of the result code.</p>

<p class="note"><strong>Note:</strong> There's no need to check whether your activity was started

with {@link

android.app.Activity#startActivity startActivity()} or {@link

android.app.Activity#startActivityForResult startActivityForResult()}. Simply call {@link

android.app.Activity#setResult(int,Intent) setResult()} if the intent that started your activity

might expect a result. If the originating activity had called {@link

android.app.Activity#startActivityForResult startActivityForResult()}, then the system delivers it

the result you supply to {@link android.app.Activity#setResult(int,Intent) setResult()}; otherwise,

the result is ignored.</p>

page.title=Interacting with Other Apps

trainingnavtop=true

startpage=true

next.title=Sending the User to Another App

next.link=sending.html

@jd:body

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<div id="tb">

<h2>Dependencies and prerequisites</h2>

<ul>

  <li>Basic understanding of the Activity lifecycle (see <a

href="{@docRoot}training/basics/activity-lifecycle/index.html">Managing the Activity

Lifecycle</a>)</li>

</ul>

<h2>You should also read</h2>

<ul>

  <li><a href="{@docRoot}training/sharing/index.html">Sharing Content</a></li>

  <li><a

href="http://android-developers.blogspot.com/2009/11/integrating-application-with-intents.html">

Integrating Application with Intents (blog post)</a></li>

  <li><a href="{@docRoot}guide/topics/intents/intents-filters.html">Intents and Intent

Filters</a></li>

</ul>

</div>

</div>

<p>An Android app typically has several <a

href="{@docRoot}guide/topics/fundamentals/activities.html">activities</a>. Each activity displays a

user interface that allows the user to perform a specific task (such as view a map or take a photo).

To take the user from one activity to another, your app must use an {@link

android.content.Intent} to define your app's "intent" to do something. When you pass an

{@link android.content.Intent} to the system with a method such as {@link

android.app.Activity#startActivity startActivity()}, the system uses the {@link

android.content.Intent} to identify and start the appropriate app component. Using intents even

allows your app to start an activity that is contained in a separate app.</p>

<p>An {@link android.content.Intent} can be <em>explicit</em> in order to start a specific component

(a specific {@link android.app.Activity} instance) or <em>implicit</em> in order to start any

component that can handle the intended action (such as "capture a photo").</p>

<p>This class shows you how to use an {@link android.content.Intent} to perform some basic

interactions with other apps, such as start another app, receive a result from that app, and

make your app able to respond to intents from other apps.</p>

<h2>Lessons</h2>

<dl>

  <dt><b><a href="sending.html">Sending the User to Another App</a></b></dt>

  <dd>Shows how you can create implicit intents to launch other apps that can perform an

action.</dd>

  <dt><b><a href="result.html">Getting a Result from an Activity</a></b></dt>

  <dd>Shows how to start another activity and receive a result from the activity.</dd>

  <dt><b><a href="filters.html">Allowing Other Apps to Start Your Activity</a></b></dt>

  <dd>Shows how to make activities in your app open for use by other apps by defining

intent filters that declare the implicit intents your app accepts.</dd>

</dl> 

page.title=Getting a Result from an Activity

parent.title=Interacting with Other Apps

parent.link=index.html

trainingnavtop=true

previous.title=Sending the User to Another App

previous.link=sending.html

next.title=Allowing Other Apps to Start Your Activity

next.link=filters.html

@jd:body

<div id="tb-wrapper">

  <div id="tb">

<h2>This lesson teaches you to</h2>

<ol>

  <li><a href="#StartActivity">Start the Activity</a></li>

  <li><a href="#ReceiveResult">Receive the Result</a></li>

</ol>

<h2>You should also read</h2>

<ul>

  <li><a href="{@docRoot}training/sharing/index.html">Sharing Content</a></li>

</ul>

  </div>

</div>

<p>Starting another activity doesn't have to be one-way. You can also start another activity and

receive a result back. To receive a result, call {@link android.app.Activity#startActivityForResult

startActivityForResult()} (instead of {@link android.app.Activity#startActivity

startActivity()}).</p>

<p>For example, your app can start a camera app and receive the captured photo as a result. Or, you

might start the People app in order for the user to select a

contact and you'll receive the contact details as a result.</p>

<p>Of course, the activity that responds must be designed to return a result. When it does, it

sends the result as another {@link android.content.Intent} object. Your activity receives it in

the {@link android.app.Activity#onActivityResult onActivityResult()} callback.</p>

<p class="note"><strong>Note:</strong> You can use explicit or implicit intents when you call

{@link android.app.Activity#startActivityForResult startActivityForResult()}. When starting one of

your own activities to receive a result, you should use an explicit intent to ensure that you

receive the expected result.</p>

<h2 id="StartActivity">Start the Activity</h2>

<p>There's nothing special about the {@link android.content.Intent} object you use when starting

an activity for a result, but you do need to pass an additional integer argument to the {@link

android.app.Activity#startActivityForResult startActivityForResult()} method.</p>

<p>The integer argument is a "request code" that identifies your request. When you receive the

result {@link android.content.Intent}, the callback provides the same request code so that your

app can properly identify the result and determine how to handle it.</p>

<p>For example, here's how to start an activity that allows the user to pick a contact:</p>

<pre>

static final int PICK_CONTACT_REQUEST = 1;  // The request code

...

private void pickContact() {

    Intent pickContactIntent = new Intent(Intent.ACTION_PICK, new Uri("content://contacts"));

    pickContactIntent.setType(Phone.CONTENT_TYPE); // Show user only contacts w/ phone numbers

    startActivityForResult(pickContactIntent, PICK_CONTACT_REQUEST);

}

</pre>

<h2 id="ReceiveResult">Receive the Result</h2>

<p>When the user is done with the subsequent activity and returns, the system calls your activity's 

{@link android.app.Activity#onActivityResult onActivityResult()} method. This method includes three

arguments:</p>

<ul>

  <li>The request code you passed to {@link

android.app.Activity#startActivityForResult startActivityForResult()}.</li>

  <li>A result code specified by the second activity. This is either {@link

android.app.Activity#RESULT_OK} if the operation was successful or {@link

android.app.Activity#RESULT_CANCELED} if the user backed out or the operation failed for some

reason.</li>

  <li>An {@link android.content.Intent} that carries the result data.</li>

</ul>

<p>For example, here's how you can handle the result for the "pick a contact" intent:</p>

<pre>

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    // Check which request we're responding to

    if (requestCode == PICK_CONTACT_REQUEST) {

        // Make sure the request was successful

        if (resultCode == RESULT_OK) {

            // The user picked a contact.

            // The Intent's data Uri identifies which contact was selected.

            // Do something with the contact here (bigger example below)

        }

    }

}

</pre>

<p>In this example, the result {@link android.content.Intent} returned by

Android's Contacts or People app provides a content {@link android.net.Uri} that identifies the

contact the user selected.</p>

<p>In order to successfully handle the result, you must understand what the format of the result

{@link android.content.Intent} will be. Doing so is easy when the activity returning a result is

one of your own activities. Apps included with the Android platform offer their own APIs that

you can count on for specific result data. For instance, the People app (Contacts app on some older

versions) always returns a result with the content URI that identifies the selected contact, and the

Camera app returns a {@link android.graphics.Bitmap} in the {@code "data"} extra (see the class

about <a href="{@docRoot}training/camera/index.html">Capturing Photos</a>).</p>

<h4>Bonus: Read the contact data</h4>

<p>The code above showing how to get a result from the People app doesn't go into

details about how to actually read the data from the result, because it requires more advanced

discussion about <a href="{@docRoot}guide/topics/providers/content-providers.html">content

providers</a>. However, if you're curious, here's some more code that shows how to query the

result data to get the phone number from the selected contact:</p>

<pre>

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    // Check which request it is that we're responding to

    if (requestCode == PICK_CONTACT_REQUEST) {

        // Make sure the request was successful

        if (resultCode == RESULT_OK) {

            // Get the URI that points to the selected contact

            Uri contactUri = data.getData();

            // We only need the NUMBER column, because there will be only one row in the result

            String[] projection = {Phone.NUMBER};

            // Perform the query on the contact to get the NUMBER column

            // We don't need a selection or sort order (there's only one result for the given URI)

            // CAUTION: The query() method should be called from a separate thread to avoid blocking

            // your app's UI thread. (For simplicity of the sample, this code doesn't do that.)

            // Consider using {@link android.content.CursorLoader} to perform the query.

            Cursor cursor = getContentResolver()

                    .query(contactUri, projection, null, null, null);

            cursor.moveToFirst();

            // Retrieve the phone number from the NUMBER column

            int column = cursor.getColumnIndex(Phone.NUMBER);

            String number = cursor.getString(column);

            // Do something with the phone number...

        }

    }

}

</pre>

<p class="note"><strong>Note:</strong> Before Android 2.3 (API level 9), performing a query

on the {@link android.provider.ContactsContract.Contacts Contacts Provider} (like the one shown

above) requires that your app declare the {@link

android.Manifest.permission#READ_CONTACTS} permission (see <a

href="{@docRoot}guide/topics/security/security.html">Security and Permissions</a>). However,

beginning with Android 2.3, the Contacts/People app grants your app a temporary

permission to read from the Contacts Provider when it returns you a result. The temporary permission

applies only to the specific contact requested, so you cannot query a contact other than the one

specified by the intent's {@link android.net.Uri}, unless you do declare the {@link

android.Manifest.permission#READ_CONTACTS} permission.</p>