docs: Revised "Optimizing Content for the Assistant" page.

<div id="tb">

    <h2>In this document</h2>

    <ol>

      <li><a href="#assist_api">Using the Assist API</a>

      <li><a href="#assist_api">Using the Assistant</a>

      <ol>

        <li><a href="#assist_api_lifecycle">Assist API Lifecycle</a></li>

        <li><a href="#source_app">Source App</a></li>

        <li><a href="#destination_app">Destination App</a></li>

        <li><a href="#source_app">Source app</a></li>

        <li><a href="#destination_app">Destination app</a></li>

      </ol>

      </li>

      <li><a href="#implementing_your_own_assistant">Implementing your

      own assistant</a></li>

      <li><a href="#implementing_your_own_assistant">Implementing Your

      Own Assistant</a></li>

    </ol>

  </div>

</div>

<p>

  Android 6.0 Marshmallow introduces a new way for users to engage with apps

  through the assistant.

</p>

  through the assistant. The assistant is a top-level window that users can view to obtain

  contextually relevant actions for the current activity. These actions might include deep links

  to other apps on the device.</p>

<p>

  Users summon the assistant with a long-press on the Home button or by saying

  the {@link android.service.voice.AlwaysOnHotwordDetector keyphrase}. In

  response to the long-press, the system opens a top-level window that displays

  contextually relevant actions for the current activity. These potential

  actions might include deep links to other apps on the device.

  Users activate the assistant with a long press on the Home button or by saying a

  <a href="{@docRoot}reference/android/service/voice/AlwaysOnHotwordDetector.html">keyphrase</a>.

  In response, the system opens a top-level window that displays contextually

  relevant actions.

</p>

<p>

  This guide explains how Android apps use Android's Assist API to improve the

  assistant user experience.

  Google App implements the assistant overlay window through a feature called

  Now on Tap, which works with the Android platform-level functionality. The system allows

  the user to select an assistant app, which obtains contextual information from your app

  using Android’s Assist API.

</p>

<h2 id="assist_api">Using the Assist API</h2>

<p>

  The example below shows how Google Now integrates with the Android assistant

  using a feature called Now on Tap.

  This guide explains how Android apps use Android's Assist API to improve the assistant

  user experience.

<p/>

</p>

<h2 id="assist_api">Using the Assistant</h2>

<p>

  The assistant overlay window in our example (2, 3) is implemented by Google

  Now through a feature called Now on Tap, which works in concert with the

  Android platform-level functionality. The system allows the user to select

  the assistant app (Figure 2) that obtains contextual information from the

  <em>source</em> app using the Assist API which is a part of the platform.

  Figure 1 illustrates a typical user interaction with the assistant. When the user long-presses

  the Home button, the Assist API callbacks are invoked

  in the <em>source</em> app (step 1). The assistant renders the overlay window (steps 2 and 3),

  and then the user selects the action to perform. The assistant executes the selected action,

  such as firing an intent with a deep link to the (<em>destination</em>) restaurant app (step 4).

</p>

<div>

  <img src="{@docRoot}images/training/assistant/image01.png">

  <p class="img-caption" style="text-align:center;">

    Figure 1. Assistant interaction example with the Now on Tap feature of

    Google Now

    the Google App

  </p>

</div>

<p>

  An Android user first configures the assistant and can change system options

  such as using text and view hierarchy as well as the screenshot of the

  current screen (Figure 2).

</p>

<p>

  From there, the assistant receives the information only when the user

  activates assistance, such as when they tap and hold the Home button ( shown

  in Figure 1, step 1).

  Users can configure the assistant by selecting <strong>Settings > Apps > Default Apps >

  Assist &amp; voice input</strong>. Users can change system options such as accessing

  the screen contents as text and accessing a screenshot, as shown in Figure 2.

</p>

<div style="float:right;margin:1em;max-width:300px">

<div id="assist-input-settings" style="float:right;margin:1em;max-width:300px">

  <img src="{@docRoot}images/training/assistant/image02.png">

  <p class="img-caption" style="text-align:center;">

    Figure 2. Assist &amp; voice input settings (<em>Settings/Apps/Default

    Apps/Assist &amp; voice input</em>)

    Figure 2. Assist & voice input settings

  </p>

</div>

<h3 id="assist_api_lifecycle">Assist API Lifecycle</h3>

<p>

  Going back to our example from Figure 1, the Assist API callbacks are invoked

  in the <em>source</em> app after step 1 (user long-presses the Home button)

  and before step 2 (the assistant renders the overlay window). Once the user

  selects the action to perform (step 3), the assistant executes it, for

  example by firing an intent with a deep link to the (<em>destination</em>)

  restaurant app (step 4).

</p>

<h3 id="source_app">Source App</h3>

<h3 id="source_app">Source app</h3>

<p>

  In most cases, your app does not need to do anything extra to integrate with

  the assistant if you already follow <a href=

  To ensure that your app works with the assistant as a source of information for the user,

  you need only follow <a href=

  "{@docRoot}guide/topics/ui/accessibility/apps.html">accessibility best

  practices</a>. This section describes how to provide additional information

  to help improve the assistant user experience, as well as scenarios, such as

  custom Views, that need special handling.

  to help improve the assistant user experience as well as scenarios

  that need special handling, such as custom Views.

</p>

<h4 id="share_additional_information_with_the_assistant">Share Additional Information with the Assistant</h4>

<h4 id="share_additional_information_with_the_assistant">Share additional information

 with the assistant</h4>

<p>

  In addition to the text and the screenshot, your app can share

  <em>additional</em> information with the assistant. For example, your music

  app can choose to pass current album information, so that the assistant can

  other information with the assistant. For example, your music

  app can choose to pass current album information so that the assistant can

  suggest smarter actions tailored to the current activity.

</p>

  To provide additional information to the assistant, your app provides

  <em>global application context</em> by registering an app listener and

  supplies activity-specific information with activity callbacks as shown in

  Figure 3.

  Figure 3:

</p>

<div>

  <img src="{@docRoot}images/training/assistant/image03.png">

  <p class="img-caption" style="text-align:center;">

    Figure 3. Assist API lifecycle sequence diagram.

    Figure 3. Assist API lifecycle sequence diagram

  </p>

</div>

  To provide global application context, the app creates an implementation of

  {@link android.app.Application.OnProvideAssistDataListener} and registers it

  using {@link

  android.app.Application#registerOnProvideAssistDataListener(android.app.Application.OnProvideAssistDataListener)}.

  In order to provide activity-specific contextual information, activity

  overrides {@link android.app.Activity#onProvideAssistData(android.os.Bundle)}

  android.app.Application#registerOnProvideAssistDataListener(android.app.Application.OnProvideAssistDataListener) registerOnProvideAssistDataListener()}.

  To provide activity-specific contextual information, the activity

  overrides {@link android.app.Activity#onProvideAssistData(android.os.Bundle) onProvideAssistData()}

  and {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent)}.

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent) onProvideAssistContent()}.

  The two activity methods are called <em>after</em> the optional global

  callback (registered with {@link

  android.app.Application#registerOnProvideAssistDataListener(android.app.Application.OnProvideAssistDataListener)})

  is invoked. Since the callbacks execute on the main thread, they should

  callback is invoked. Because the callbacks execute on the main thread, they should

  complete <a href="{@docRoot}training/articles/perf-anr.html">promptly</a>.

  The callbacks are invoked only when the activity is <a href=

  "{@docRoot}reference/android/app/Activity.html#ActivityLifecycle">running</a>.

</p>

<h5 id="providing_context">Providing Context</h5>

<h5 id="providing_context">Providing context</h5>

<p>

  {@link android.app.Activity#onProvideAssistData(android.os.Bundle)} is called

  when the user is requesting the assistant to build a full {@link

  When the user activates the assistant,

  {@link android.app.Activity#onProvideAssistData(android.os.Bundle) onProvideAssistData()} is called to build a full

  {@link

  android.content.Intent#ACTION_ASSIST} Intent with all of the context of the

  current application represented as an instance of the {@link

  android.app.assist.AssistStructure}. You can override this method to place

  into the bundle anything you would like to appear in the

  <code>EXTRA_ASSIST_CONTEXT</code> part of the assist Intent.

  anything you like into the bundle to appear in the

  {@link android.content.Intent#EXTRA_ASSIST_CONTEXT} part of the assist intent.

</p>

<h5 id="describing_content">Describing Content</h5>

<h5 id="describing_content">Describing content</h5>

<p>

  Your app can implement {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent)}

  to improve assistant user experience by providing references to content

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent) onProvideAssistContent()}

  to improve the assistant user experience by providing content-related references

  related to the current activity. You can describe the app content using the

  common vocabulary defined by <a href="https://schema.org">Schema.org</a>

  common vocabulary defined by <a href="https://schema.org" class="external-link">Schema.org</a>

  through a JSON-LD object. In the example below, a music app provides

  structured data to describe the music album the user is currently

  looking at.

  structured data to describe the music album that the user is currently

  viewing:

</p>

<pre class="prettyprint">

</pre>

<p>

  Custom implementations of {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent)}

  may also adjust the provided {@link

  android.app.assist.AssistContent#setIntent(android.content.Intent) content

  intent} to better reflect the top-level context of the activity, supply

  {@link android.app.assist.AssistContent#setWebUri(android.net.Uri) the URI}

  of the displayed content, and fill in its {@link

  android.app.assist.AssistContent#setClipData(android.content.ClipData)} with

  additional content of interest that the user is currently viewing.

 You can also improve the user experience with custom implementations of

 {@link

 android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent) onProvideAssistContent()},

 which can provide the following benefits:

</p>

<ul>

  <li><a href="{@docRoot}reference/android/app/assist/AssistContent.html#setIntent(android.content.Intent)">

  Adjusts the provided content

  intent</a> to

  better reflect the top-level context of the activity.</li>

  <li><a href="{@docRoot}reference/android/app/assist/AssistContent.html#setWebUri(android.net.Uri)">

  Supplies the URI</a>

  of the displayed content.</li>

  <li>Fills in {@link

  android.app.assist.AssistContent#setClipData(android.content.ClipData) setClipData()} with additional

  content of interest that the user is currently viewing.</li>

</ul>

<p class="note">

  <strong>Note: </strong>Apps that use a custom text selection implementation likely need

  to implement {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent) onProvideAssistContent()}

  and call {@link android.app.assist.AssistContent#setClipData(android.content.ClipData) setClipData()}.

</p>

<h4 id="default_implementation">Default Implementation</h4>

<h4 id="default_implementation">Default implementation</h4>

<p>

  If neither {@link

  android.app.Activity#onProvideAssistData(android.os.Bundle)} nor {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent)}

  callbacks are implemented, the system will still proceed and pass the

  information collected automatically to the assistant unless the current

  If neither the {@link

  android.app.Activity#onProvideAssistData(android.os.Bundle) onProvideAssistData()} nor the {@link

  android.app.Activity#onProvideAssistContent(android.app.assist.AssistContent) onProvideAssistContent()}

  callback is implemented, the system still proceeds and passes the

  automatically collected information to the assistant unless the current

  window is flagged as <a href="#excluding_views">secure</a>.

  As shown in Figure 3, the system uses the default implementations of {@link

  android.view.View#onProvideStructure(android.view.ViewStructure)} and {@link

  android.view.View#onProvideVirtualStructure(android.view.ViewStructure)} to

  android.view.View#onProvideStructure(android.view.ViewStructure) onProvideStructure()} and {@link

  android.view.View#onProvideVirtualStructure(android.view.ViewStructure) onProvideVirtualStructure()} to

  collect text and view hierarchy information. If your view implements custom

  text drawing, you should override {@link

  android.view.View#onProvideStructure(android.view.ViewStructure)} to provide

  text drawing, override {@link

  android.view.View#onProvideStructure(android.view.ViewStructure) onProvideStructure()} to provide

  the assistant with the text shown to the user by calling {@link

  android.view.ViewStructure#setText(java.lang.CharSequence)}.

  android.view.ViewStructure#setText(java.lang.CharSequence) setText(CharSequence)}.

</p>

<p>

  <strong>In most cases, implementing accessibility support will enable the

  assistant to obtain the information it needs.</strong> This includes

  providing {@link android.R.attr#contentDescription

  android:contentDescription} attributes, populating {@link

  android.view.accessibility.AccessibilityNodeInfo} for custom views, making

  sure custom {@link android.view.ViewGroup ViewGroups} correctly {@link

  android.view.ViewGroup#getChildAt(int) expose} their children, and following

  the best practices described in <a href=

  "{@docRoot}guide/topics/ui/accessibility/apps.html">“Making Applications

  Accessible”</a>.

</p>

  <em>In most cases, implementing accessibility support enables the

  assistant to obtain the information it needs.</em> To implement accessibility support,

  observe the best practices described in <a href=

  "{@docRoot}guide/topics/ui/accessibility/apps.html">Making Applications

  Accessible</a>, including the following:</p>

<ul>

  <li>Provide {@link android.R.attr#contentDescription

  android:contentDescription} attributes.</li>

  <li>Populate {@link

  android.view.accessibility.AccessibilityNodeInfo} for custom views.</li>

  <li>Make

  sure that custom {@link android.view.ViewGroup ViewGroup} objects correctly

  <a href="{@docRoot}reference/android/view/ViewGroup.html#getChildAt(int)">expose</a>

  their children.</li>

</ul>

<h4 id="excluding_views">Excluding views from the assistant</h4>

<p>

  An activity can exclude the current view from the assistant. This is accomplished

  To handle sensitive information, your app can exclude the current view from the assistant

  by setting the {@link android.view.WindowManager.LayoutParams#FLAG_SECURE

  FLAG_SECURE} layout parameter of the WindowManager and must be done

  explicitly for every window created by the activity, including Dialogs. Your

  app can also use {@link android.view.SurfaceView#setSecure(boolean)

  SurfaceView.setSecure} to exclude a surface from the assistant. There is no

  FLAG_SECURE} layout parameter of the {@link android.view.WindowManager}. You must set {@link

  android.view.WindowManager.LayoutParams#FLAG_SECURE

  FLAG_SECURE} explicitly for

  every window created by the activity, including dialogs. Your app can also use

  {@link android.view.SurfaceView#setSecure(boolean) setSecure()} to exclude

  a surface from the assistant. There is no

  global (app-level) mechanism to exclude all views from the assistant. Note

  that <code>FLAG_SECURE</code> does not cause the Assist API callbacks to stop

  firing. The activity which uses <code>FLAG_SECURE</code> can still explicitly

  that {@link android.view.WindowManager.LayoutParams#FLAG_SECURE

  FLAG_SECURE} does not cause the Assist API callbacks to stop

  firing. The activity that uses {@link android.view.WindowManager.LayoutParams#FLAG_SECURE

  FLAG_SECURE} can still explicitly

  provide information to the assistant using the callbacks described earlier

  this guide.

</p>

<h4 id="voice_interactions">Voice Interactions</h4>

<p class="note"><strong>Note: </strong>For enterprise accounts (Android for Work),

 the administrator can disable

 the collection of assistant data for the work profile by using the {@link

 android.app.admin.DevicePolicyManager#setScreenCaptureDisabled(android.content.ComponentName, boolean)

 setScreenCaptureDisabled()} method of the {@link android.app.admin.DevicePolicyManager} API.</p>

<h4 id="voice_interactions">Voice interactions</h4>

<p>

  Assist API callbacks are also invoked upon {@link

  android.service.voice.AlwaysOnHotwordDetector keyphrase detection}. For more

  information see the <a href="https://developers.google.com/voice-actions/">voice

  actions</a> documentation.

  Assist API callbacks are also invoked upon

  <a href="{@docRoot}reference/android/service/voice/AlwaysOnHotwordDetector.html">keyphrase

  detection</a>. For more information, see the

  <a href="https://developers.google.com/voice-actions/" class="external-link">Voice

  Actions</a> documentation.

</p>

<h4 id="z-order_considerations">Z-order considerations</h4>

<p>

  The assistant uses a lightweight overlay window displayed on top of the

  current activity. The assistant can be summoned by the user at any time.

  Therefore, apps should not create permanent {@link

  android.Manifest.permission#SYSTEM_ALERT_WINDOW system alert}

  windows interfering with the overlay window shown in Figure 4.

  current activity. Because the user can activate the assistant at any time,

  don't create permanent <a

  href="{@docRoot}reference/android/Manifest.permission.html#SYSTEM_ALERT_WINDOW">

  system alert</a> windows that interfere with the overlay window, as shown in

  Figure 4.

</p>

<div style="">

  <img src="{@docRoot}images/training/assistant/image04.png">

  <p class="img-caption" style="text-align:center;">

    Figure 4. Assist layer Z-order.

    Figure 4. Assist layer Z-order

  </p>

</div>

<p>

  If your app uses {@link

  android.Manifest.permission#SYSTEM_ALERT_WINDOW system alert} windows, it

  must promptly remove them as leaving them on the screen will degrade user

  experience and annoy the users.

  If your app uses <a

  href="{@docRoot}reference/android/Manifest.permission.html#SYSTEM_ALERT_WINDOW">

  system alert</a> windows, remove them promptly because leaving them on the

  screen degrades the user experience.

</p>

<h3 id="destination_app">Destination App</h3>

<h3 id="destination_app">Destination app</h3>

<p>

  The matching between the current user context and potential actions displayed

  in the overlay window (shown in step 3 in Figure 1) is specific to the

  assistant’s implementation. However, consider adding <a href=

  "{@docRoot}training/app-indexing/deep-linking.html">deep linking</a> support

  to your app. The assistant will typically take advantage of deep linking. For

  example, Google Now uses deep linking and <a href=

  "https://developers.google.com/app-indexing/">App Indexing</a> in order to

  The assistant typically takes advantage of deep linking to find destination apps. To make your

  app a potential destination app, consider adding <a href=

  "{@docRoot}training/app-indexing/deep-linking.html">deep linking</a> support. The matching

  between the current user context and deep links or other potential actions displayed in the

  overlay window (shown in step 3 in Figure 1) is specific to the assistant’s implementation.

  For

  example, the Google App uses deep linking and <a href=

  "https://developers.google.com/app-indexing/" class="external-link">Firebase App Indexing</a> in order to

  drive traffic to destination apps.

</p>

<h2 id="implementing_your_own_assistant">Implementing your own assistant </h2>

<h2 id="implementing_your_own_assistant">Implementing Your Own Assistant </h2>

<p>

  Some developers may wish to implement their own assistant. As shown in Figure

  2, the active assistant app can be selected by the Android user. The

  You may wish to implement your own assistant. As shown in <a href="#assist-input-settings">Figure

  2</a>, the user can select the active assistant app. The

  assistant app must provide an implementation of {@link

  android.service.voice.VoiceInteractionSessionService} and {@link

  android.service.voice.VoiceInteractionSession} as shown in <a href=

  "https://android.googlesource.com/platform/frameworks/base/+/android-5.0.1_r1/tests/VoiceInteraction?autodive=0%2F%2F%2F%2F%2F%2F">

  this</a> example and it requires the {@link

  android.Manifest.permission#BIND_VOICE_INTERACTION} permission. It can then

  "https://android.googlesource.com/platform/frameworks/base/+/marshmallow-release/tests/VoiceInteraction/" class="external-link">

  this <code>VoiceInteraction</code> example</a>. It also requires the {@link

  android.Manifest.permission#BIND_VOICE_INTERACTION} permission. The assistant can then

  receive the text and view hierarchy represented as an instance of the {@link

  android.app.assist.AssistStructure} in {@link

  android.service.voice.VoiceInteractionSession#onHandleAssist(android.os.Bundle,

  android.app.assist.AssistStructure,android.app.assist.AssistContent) onHandleAssist()}.

  The assistant receives the screenshot through {@link

  It receives the screenshot through {@link

  android.service.voice.VoiceInteractionSession#onHandleScreenshot(android.graphics.Bitmap)

  onHandleScreenshot()}.

</p>