android_frameworks_base/docs/html/training/auto/messaging/index.jd

page.title=Providing Messaging for Auto
page.tags="auto", "car", "automotive", "messaging"
page.article=true

page.metaDescription=Learn how to extend your messaging app for use in Android Auto devices.
page.image=auto/images/assets/icons/messaging_app_notifications.png

@jd:body

<div id="tb-wrapper">
<div id="tb">
  <h2>Dependencies and Prerequisites</h2>
  <ul>
    <li>Android 5.0 (API level 21) or higher</li>
  </ul>

    <h2>This class teaches you to:</h2>

    <ul>
      <li><a href="#overview">Provide Messaging Services</a></li>
      <li><a href="#manifest">Configure Your Manifest</a></li>
      <li><a href="#support-lib">Import Support Library for Messaging</a></li>
      <li><a href="#messaging">Notify Users of Messages</a></li>
      <li><a href="#handle_actions">Handle User Actions</a></li>
    </ul>

    <h2>Related Samples</h2>

    <ul>
      <li><a href="{@docRoot}samples/MessagingService/index.html">
        MessagingService</a></li>
    </ul>

    <h2>See Also</h2>

    <ul>
      <li><a href="{@docRoot}shareables/auto/AndroidAuto-messaging-apps.pdf">
        User Experience Guidelines: Messaging Apps</a></li>
      <li><a href="{@docRoot}guide/topics/ui/notifiers/notifications.html">
        Notifications</a></li>
    </ul>
</div>
</div>

<a class="notice-developers-video wide"
    href="https://www.youtube.com/watch?v=gSVLuaOTIPk">
<div>
    <h3>Video</h3>
    <p>DevBytes: Android Auto Messaging</p>
</div>
</a>

<p>
  Staying connected through messages is important to many drivers. Chat apps can let users
  know if a child need to be picked up, or if a dinner location has been changed. Apps that provide
  sports information might tell the user who just won the big game, and let the user ask questions
  about other games being played. The Android framework enables messaging apps to extend their
  services into car dashboards using a standard user interface that lets drivers keep their eyes
  on the road.
</p>

<p>
  Apps that support messaging can be extended to pass messaging notifications to Auto
  dashboard systems, alerting them to new messages and allowing them to respond. You can configure
  your messaging app to provide these services when an Android mobile device with your app
  installed is connected to an Auto dashboard. Once connected, your app can provide text
  information to users and allow them to respond. The Auto dashboard system handles displaying the
  notification and the interface for replies.
</p>

<p>
  This lesson assumes that you have built an app that displays messages to the user and receive the
  user's replies, such as a chat app. It shows you how to extend your app to hand those messages
  off to an Auto device for display and replies.
</p>


<h2 id="overview">Provide Messaging Services</h2>

<p>
  Messaging apps do not run directly on the Android dashboard hardware. They are installed on
  separate, Android mobile device. When the mobile device is plugged into a dashboard,
  the installed messaging apps can offer services for viewing and responding to messages
  through the Auto user interface.
</p>

<p>To enable your app to provide messaging services for Auto devices:</p>

<ul>
  <li>Configure your app manifest to indicate that your app provides messaging services which are
  compatible with Android Auto dashboard devices.
  </li>
  <li>Build and send a specific type of <a href=
  "{@docRoot}guide/topics/ui/notifiers/notifications.html">notification</a> for display on Auto
  devices.
  </li>
  <li>Configure your app to receive {@link android.content.Intent} objects that indicate a user
    has read or replied to a message.
</ul>

<h3 id="#concepts">Concepts and Objects</h3>

<p>Before you start designing your app, it's helpful to understand how Auto
handles messaging.</p>

<p>Each individual chunk of communication is a <em>message</em>. A message is a
short length of text, suitable for the Auto device to read aloud. In a chat app,
this might be a single message from one person to another: <code>"Fitzy -- Jane
can't come to the ball, her youngest has the croup. :-( --Liz"</code> In a
sports app, a message might be a single bit of news about a game: <code>"Granger
scores for Harpies at 7 minutes in."</code></p>

<p>A <em>conversation</em> is a group of messages that are all grouped together
in some way. Auto uses the conversation information to group the messages
together when presenting them to the user. In a chat app, a conversation might
be all the messages between the user and another person (for example, all
the messages back and forth between Darcy and Elizabeth). In a sports app, a
conversation might be all the messages about a particular game. Every message
belongs to a conversation, even if it's the only message in that conversation.
Each conversation has a <em>conversation name</em>.
The conversation name is used by Android Auto to
present the messages; it's up to your app to choose an appropriate conversation
name. In a chat app, the conversation name is usually the person your user is
talking to.
In a sports app, this might be the name of the teams playing in the game.</p>

<p>The v4 support library defines an {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} object. This object holds all messages in a conversation
which have not yet been heard by the user. To give those messages to the user,
you attach that {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} to a notification. However, you do not attach messages to
the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} directly. Instead, you must first set up an {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder
UnreadConversation.Builder} object for the conversation. The messages are added to the builder,
then when you are ready to send the messages, you use the builder to create the
actual {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} and attach the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} to the notification.</p>

<p class="note"><strong>Note:</strong> When Auto presents messages to the
user, it uses the notification <em>tag</em> and <em>ID</em> to determine which conversation the
messages belong to. It is important to use the same tag and ID for all messages in
a conversation, and to not use that tag for other conversations.</p>

<h3 id="#workflow">Workflow</h3>

<p>This section describes how the mobile device interacts with Auto to present
messages to the user.</p>

<ol>

<li>The app receives a message that it wants to pass on to the user. It attaches
the message to an  {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} object and attaches it to a notification. That notification
is associated with a {@link
android.support.v4.app.NotificationCompat.CarExtender CarExtender} object, which
indicates that the notification can be handled by Android Auto.</li>

<li>The app posts the notification. The Android notification framework passes the
message to Auto. Auto uses the notification tag and ID to determine which conversation
the message belongs to, and presents the message to the user in an appropriate
way.</li>

<li>When the user listens to the message, Auto triggers the app's message heard
pending intent. The app should discard the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} object and its builder at this time, since the messages
contained in those objects have been heard by the user.</li>

<li>If the user sends a reply, Auto triggers the app's "message reply" intent and
attaches a transcript of the user's response.  The app can take appropriate
action, based on the app's logic. For example, a chat app might interpret the
reply as a message to go to the other conversation participants, while a sports
app might try to interpret the "reply" as a request for other information
("What's the score in the Sharks game?").</li>

</ol>

<h2 id="#manifest">Configure Your Manifest</h2>

<p>
  You configure your app <a href="{@docRoot}guide/topics/manifest/manifest-intro.html">manifest</a>
  to indicate that it supports messaging services for Auto devices and handle message actions. This
  section describes what changes to make to your manifest to support messaging for Auto devices.
</p>

<h3 id="manifest-messaging">Declare Auto messaging support</h3>

<p>
  When a user connects a Android mobile device to a dashboard running Android, the dashboard
  device looks for apps that declare support for vehicle services, such as messaging. You indicate
  that your app supports cars capabilities using the following manifest entry:
</p>

<pre>
&lt;application&gt;
    ...
    &lt;meta-data android:name="com.google.android.gms.car.application"
        android:resource="@xml/automotive_app_desc" /&gt;
    ...
&lt;application&gt;
</pre>

<p>
  This manifest entry refers to a secondary xml file, where you declare what Auto capabilities your
  app supports. For an app that supports messaging for Auto devices, add an xml file to the {@code
  res/xml/} your app's development project directory as {@code automotive_app_desc.xml}, with the
  following content:
</p>

<pre>
&lt;automotiveApp&gt;
    &lt;uses name="notification"/&gt;
&lt;/automotiveApp&gt;
</pre>

<p>
  For more information about declaring capabilities for Auto devices, see <a href=
  "{@docRoot}training/auto/start/index.html#auto-metadata">Getting Started with Auto</a>.
</p>


<h3 id="manifest-intent">Define read and reply intent filters</h3>

<p>
  Auto devices use {@link android.content.Intent} objects that indicate a user has read or replied
  to a message provided by your app. Your app defines intent types for reading and replying to
  messages and adds this information to messaging notifications for Auto devices, so that the
  dashboard system can notify your app when a user takes one of these actions.
</p>

<p>
  You define the read action and reply action intents types for your app and the {@link
  android.content.BroadcastReceiver} classes that handle them in the manifest. The following code
  example demonstrates how to declare these intents and their associated receivers.
</p>

<pre>
&lt;application&gt;
    ...
    &lt;receiver android:name=".MyMessageHeardReceiver"&gt;
        &lt;intent-filter&gt;
          &lt;action android:name="com.myapp.messagingservice.MY_ACTION_MESSAGE_HEARD"/&gt;
        &lt;/intent-filter&gt;
    &lt;/receiver&gt;

    &lt;receiver android:name=".MyMessageReplyReceiver"&gt;
        &lt;intent-filter&gt;
          &lt;action android:name="com.myapp.messagingservice.MY_ACTION_MESSAGE_REPLY"/&gt;
        &lt;/intent-filter&gt;
    &lt;/receiver&gt;
    ...
&lt;/application&gt;
</pre>

<p>   In this example, <code>"MyMessageReadReceiver"</code> and
<code>"MyMessageReplyReceiver"</code> are the names of the {@link
android.content.BroadcastReceiver} subclasses you define to handle the
intents. You can choose whatever you like   as the action names, but it's best
to prepend your package name to ensure that   the action names are unique. For
more information about handling actions, see <a href="#handle_actions">Handle
User Actions</a>. </p>

<h2 id="support-lib">Import Support Library for Messaging</h3>

<p>
  Building notifications for use with Auto devices requires classes from the
  <a href="{@docRoot}tools/support-library/features.html#v4">v4 support library</a>. Use the
  <a href="{@docRoot}tools/help/sdk-manager.html">Android SDK Manager</a> to update the
  <em>Extras > Android Support Repository</em> to version 9 or higher and the
  <em>Extras > Android Support Library</em> to version 21.0.2 or higher.
</p>

<p>
  After you have updated the support libraries, import them into your Android Studio development
  project by adding this dependency to your
  <a href="{@docRoot}sdk/installing/studio-build.html#configBuild">build.gradle</a> file:
</p>

<pre>
dependencies {
    ...
    compile 'com.android.support:support-v4:21.0.2'
}
</pre>

<p>
  For information about importing the support library into development projects for other
  development environments, see <a href="{@docRoot}tools/support-library/setup.html">Support
  Library Setup</a>.
</p>



<h2 id="messaging">Notify Users of Messages</h2>

<p>
  A messaging app provides messages to a connected Auto dashboard using the <a href=
  "{@docRoot}guide/topics/ui/notifiers/notifications.html">notifications</a> framework. When your
  messaging app has a message for a user, you build a specially configured notification that is
  received by the dashboard system and presented to the user. The Auto device manages the
  presentation on the dashboard screen and may play the message via text-to-speech. The dashboard
  system also handles voice interaction if the user replies to a message using verbal input.
</p>

<p>
  The messaging user interface for Auto presents users with two levels of information about
  messages. The first level of notification tells users what <em>conversations</em> are
  available, and who they are with, but not the content of the messages. Typically, a
  conversation is one or more messages from another user to the Auto user.
</p>

<p>
  The second level of the notification is the actual content of messages in the conversation. If a
  user indicates they want to hear the messages in a conversation, the Auto user interface plays
  the messages using text-to-speech.
</p>

<p>
  This section describes how to notify Auto users that conversations are available and
  provide the content of messages in those conversations.
</p>

<h4 id="conversation-intents">Create conversation read and reply intents</h4>

<p>
  Unread conversation objects contain intents for reading and replying to a conversation. You
  create a {@link android.app.PendingIntent} object for each of these actions, so the Auto device
  can notify your app of action taken by the Auto user on a particular conversation.
</p>

<p>
  The following example code demonstrates how to define a {@link android.app.PendingIntent} to let
  your app know if a conversation was read to the Auto user:
</p>

<pre>
Intent msgHeardIntent = new Intent()
    .addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES)
    .setAction("com.myapp.messagingservice.MY_ACTION_MESSAGE_HEARD")
    .putExtra("conversation_id", thisConversationId);

PendingIntent msgHeardPendingIntent =
    PendingIntent.getBroadcast(getApplicationContext(),
        thisConversationId,
        msgHeardIntent,
        PendingIntent.FLAG_UPDATE_CURRENT);
</pre>

<p>In this example, {@code thisConversationId} is an integer that identifies the
current conversation.   The value of {@link android.content.Intent#setAction
Intent.setAction()} is the intent filter identifier for heard messages which you
defined in your app manifest, as shown in <a href="#manifest-intent">Define read
and reply intent filters</a>. </p>

<p>
  If your app supports replying to conversations, you also create a {@link
  android.app.PendingIntent} for each conversation to notify your app that the user has replied.
  The following code example shows you how to build this intent for use with a particular
  conversation:
</p>

<pre>
Intent msgReplyIntent = new Intent()
    .addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES)
    .setAction("com.myapp.messagingservice.MY_ACTION_MESSAGE_REPLY")
    .putExtra("conversation_id", thisConversationId);

PendingIntent msgReplyPendingIntent = PendingIntent.getBroadcast(
    getApplicationContext(),
    thisConversationId,
    msgReplyIntent,
    PendingIntent.FLAG_UPDATE_CURRENT);
</pre>

<p>   Once again, {@code thisConversationId} is an integer that uniquely identifies
this conversation, and    the value you pass to {@link
android.content.Intent#setAction Intent.setAction()} is the intent filter
identifier you defined for replies in your   app manifest. </p>

<h3 id="build_conversation">Set up the conversation builder</h4>

<p>
  Messaging notifications for Auto organize messages into conversations using the {@link
  android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation} class,
  that represents an unread or new
  portion of a conversation from a particular sender. It contains a list of messages from the
  sender.
</p>

<p>
  You generally do not configure the {@link
  android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation UnreadConversation}
  directly. Instead, you configure an
  {@link android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder
  UnreadConversation.Builder} with the information about the conversation,
  as shown in the following example code.
</p>

<pre>
// Build a RemoteInput for receiving voice input in a Car Notification
RemoteInput remoteInput = new RemoteInput.Builder(MY_VOICE_REPLY_KEY)
        .setLabel(getApplicationContext().getString(R.string.notification_reply))
        .build();

// Create an unread conversation object to organize a group of messages
// from a particular sender.
UnreadConversation.Builder unreadConvBuilder =
    new UnreadConversation.Builder(conversationName)
        .setReadPendingIntent(msgHeardPendingIntent)
        .setReplyAction(msgReplyPendingIntent, remoteInput);
</pre>

<p class="note">
  <strong>Note:</strong> You won't actually create the {@link
  android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
  UnreadConversation} until you are almost ready to send the message.
</p>

<p>
  This conversation object includes a {@link android.app.PendingIntent}, which allows the Auto
  device to signal your app that the conversation has been read by the Auto user. The construction
  of this intent is discussed in the <a href="#conversation-intents">Creating conversation read and
  reply intents</a> section.
</p>

<p>
  If your app supports replying to a conversation, you must call the
  {@link android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder#setReplyAction
  UnreadConversation.Builder.setReplyAction()}
  method and provide a pending intent to pass that user action back to your app. The
  {@link android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
  UnreadConversation}
  object you create must also include a {@link
  android.support.v4.app.RemoteInput} object. When the Auto user
  receiving this conversation speaks a reply, the remote input objects lets your app get a text
  version of the voice reply.
</p>

<h3 id="sending_messages">Sending Messages</h4>

<p>
  When a message arrives for a conversation, you take the following steps to dispatch it as a
  notification to Auto.
</p>

<p>First, add the message to the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder
UnreadConversation.Builder} for this conversation, and update its timestamp:</p>

<pre>
unreadConvBuilder.addMessage(messageString)
    .setLatestTimestamp(currentTimestamp);
</pre>

<p class="note"><strong>Note:</strong> If you are sending several messages at
once, add them to the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder
UnreadConversation.Builder} in order, from oldest to newest.</p>

<p>Then create the {@link android.support.v4.app.NotificationCompat.Builder
NotificationCompat.Builder}
object that builds the actual notification. You need to use the
pending intents you created in the previous step.</p>

<pre>
NotificationCompat.Builder notificationBuilder =
    new NotificationCompat.Builder(getApplicationContext())
        .setSmallIcon(smallIconResourceID)
        .setLargeIcon(largeIconBitmap);
</pre>

<dl>
  <dt><code>smallIconResourceID</code></dt>
  <dd>The resource ID of a small icon to use for the conversation. This is
    typically a generic icon for the messaging app.</dd>

  <dt><code>largeIconBitmap</code></dt>
  <dd>A {@link android.graphics.Bitmap} of a large version of the icon. This
    is typically a conversation-specific graphic. For example, if this is a
    chat app, the large icon would be a picture of the person the user is
    chatting with.</dd>

  <dt><code>messageString</code></dt>
  <dd>The text of the message you want to send. (If you are sending several
    messages at once, concatenate them into a single string, with the oldest
    message first.)</dd>

  <dt><code>currentTimestamp</code></dt>
  <dd>The message timestamp. (If you are sending several messages at once,
    use the timestamp of the most recent message.)</dd>

  <dt><code>conversationName</code></dt>

  <dd>The name you chose for this conversation (for example, the name of the
    person the user is chatting with). This should be the same conversation
    name you used when you created the {@link
android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation.Builder
    UnreadConversation.Builder}.</dd>

  <dt><code>msgHeardPendingIntent</code></dt>
  <dd>The pending intent object you created in
    <a href="#conversation-intents">Create conversation read and reply
      intents</a>.</dd>
</dl>


<p>You'll also need to extend the  {@link
android.support.v4.app.NotificationCompat.Builder NotificationCompat.Builder} with the {@link
android.support.v4.app.NotificationCompat.CarExtender CarExtender}. This is where you
actually create the
{@link android.support.v4.app.NotificationCompat.CarExtender.UnreadConversation
UnreadConversation} object using the builder you
just created, and attach it to the {@link
android.support.v4.app.NotificationCompat.CarExtender CarExtender}:</p>

<pre>
notificationBuilder.extend(new CarExtender()
    .setUnreadConversation(unreadConvBuilder.build());
</pre>

<p class="note"><strong>Note:</strong> If you wish, you can set an override icon
or color for the {@link android.support.v4.app.NotificationCompat.CarExtender
CarExtender} by calling {@link
android.support.v4.app.NotificationCompat.CarExtender#setLargeIcon
setLargeIcon()} or {@link
android.support.v4.app.NotificationCompat.CarExtender#setColor setColor()}. The
override icon or color is used when the notification is handled by a car, and
has no effect if the notification is handled on the Android device. This is
useful if the notification's default icon or color are not suitable for the
car's display.</p>

<p>Once you've done all this, you use your app's {@link
android.support.v4.app.NotificationManagerCompat} to send the notification:</p>

<pre>
NotificationManagerCompat msgNotificationManager =
    NotificationManagerCompat.from(context);
msgNotificationManager.notify(notificationTag,
    notificationId, notificationBuilder.build());
</pre>

<h2 id="handle_actions">Handle User Actions</h2>

<p>
  When your create and dispatch a notification for messaging, you specify intents to be triggered
  when the Auto user hears the message and when the user dictates a reply. Your app indicates to
  the Android framework that it handles these intends by registering them through its manifest, as
  discussed in <a href="#manifest-intent">Define read and reply intent filters</a>.
</p>

<p>
  In addition to registering these intent filters, your app must provide code to handle these
  actions. Your app can do this by providing a service or {@link android.content.BroadcastReceiver}
  objects that handle these intents.</p>

<p>
  For more information about intents, see <a href=
  "{@docRoot}guide/components/intents-filters.html">Intents and Intent Filters</a>.
</p>


<h3 id="handling_msg_heard">Handling a message heard action</h3>

<p>
  When a user listens to a messaging conversation through the Auto user interface, the dashboard
  device sends a read intent based on how your app defined the messaging notification. Your app
  catches that intent and invokes the broadcast receiver class associated with it, or the service
  method set up to handle that action.
</p>

<p>
  The following code example shows how to define a {@link android.content.BroadcastReceiver} class
  to handle a received message heard intent:
</p>

<pre>
public class MyMessageHeardReceiver extends BroadcastReceiver {

    &#64;Override
    public void onReceive(Context context, Intent intent) {

        // If you set up the intent as described in
        // "Create conversation read and reply intents",
        // you can get the conversation ID by calling:
        int thisConversationId = intent.getIntExtra("conversation_id", -1);

        // Remove the notification to indicate it has been read
        // and update the list of unread conversations in your app.
    }
}
</pre>

<p>
  Once a notification is read, your app can remove it by calling
  {@link android.support.v4.app.NotificationManagerCompat#cancel
  NotificationManagerCompat.cancel()} with the notification ID.
  Within your app, you should mark the messages provided in the notification as read.
</p>


<p class="note">
  <strong>Note:</strong> An alternative to this implementation is to use a service in a
  {@link android.app.PendingIntent}.
</p>


<h3 id="handling_reply">Handling a reply action</h3>

<p>
  When a user replies to a messaging conversation through the Auto user interface, the dashboard
  system sends a reply intent based on how your app defined the messaging notification. Your app
  catches that intent and invokes the broadcast receiver class associated with it, or the service
  method set up to handle that action.
</p>

<p>
  The following code example shows how to define a {@link android.content.BroadcastReceiver} class
  to handle a received message reply intent:
</p>

<pre>
  public class MyMessageReplyReceiver extends BroadcastReceiver {


    &#64;Override
    public void onReceive(Context context, Intent intent) {
        // If you set up the intent as described in
        // "Create conversation read and reply intents",
        // you can get the conversation ID by calling:
        int thisConversationId = intent.getIntExtra("conversation_id", -1).

    }

    /**
     * Get the message text from the intent.
     * Note that you should call
     * RemoteInput.getResultsFromIntent() to process
     * the RemoteInput.
     */
    private CharSequence getMessageText(Intent intent) {
        Bundle remoteInput =
            RemoteInput.getResultsFromIntent(intent);
        if (remoteInput != null) {
            return remoteInput.getCharSequence(MY_VOICE_REPLY_KEY);
        }
        return null;
    }

}</pre>