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Commit 73d799dd authored by Scott Rowe's avatar Scott Rowe
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docs: Recents screen for tasks and activities 

Change-Id: I94774e60e6a7453a047ad394c3bbfff0cc4dfc7d
parent 597d3861

docs/html/guide/components/recents.jd

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page.title=Overview Screen

page.tags="recents","overview"



@jd:body



<div id="qv-wrapper">

<div id="qv">



  <h2>In this document</h2>

  <ol>

    <li><a href="#adding">Adding Tasks to the Overview Screen</a>

      <ol>

        <li><a href="#flag-new-doc">Using the Intent flag to add a task</a></li>

        <li><a href="#attr-doclaunch">Using the Activity attribute to add a task</a></li>

      </ol>

    </li>

    <li><a href="#removing">Removing Tasks</a>

      <ol>

        <li><a href="#apptask-remove">Using the AppTask class to remove tasks</a></li>

        <li><a href="#retain-finished">Retaining finished tasks</a></li>

      </ol>

    </li>

  </ol>



  <h2>Key classes</h2>

  <ol>

    <li>{@link android.app.ActivityManager.AppTask}</li>

    <li>{@link android.content.Intent}</li>

  </ol>



  <h2>Sample code</h2>

  <ol>

    <li><a href="{@docRoot}samples/activitytasks/index.html">Document-centric Apps</a></li>

  </ol>



</div>

</div>



<p>The overview screen (also referred to as the recents screen, recent task list, or recent apps)

is a system-level UI that lists recently accessed <a href="{@docRoot}guide/components/activities.html">

activities</a> and <a href="{@docRoot}guide/components/tasks-and-back-stack.html">tasks</a>. The

user can navigate through the list and select a task to resume, or the user can remove a task from

the list by swiping it away. With the Android 5.0 release (API level 21), multiple instances of the

same activity containing different documents may appear as tasks in the overview screen. For example,

Google Drive may have a task for each of several Google documents. Each document appears as a

task in the overview screen.</p>



<img src="{@docRoot}images/components/recents.png" alt="" width="284" />

<p class="img-caption"><strong>Figure 1.</strong> The overview screen showing three Google Drive

documents, each represented as a separate task.</p>



<p>Normally you should allow the system to define how your tasks and

activities are represented in the overview screen, and you don't need to modify this behavior.

However, your app can determine how and and when activities appear in the overview screen. The

{@link android.app.ActivityManager.AppTask} class lets you manage tasks, and the activity flags of

the {@link android.content.Intent} class let you specify when an activity is added or removed from

the overview screen. Also, the <code><a href="{@docRoot}guide/topics/manifest/activity-element.html">

&lt;activity&gt;</a></code> attributes let you set the behavior in the manifest.</p>



<h2 id="adding">Adding Tasks to the Overview Screen</h2>



<p>Using the flags of the {@link android.content.Intent} class to add a task affords greater control

over when and how a document gets opened or reopened in the overview screen. When you use the

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

attributes you can choose between always opening the document in a new task or reusing an

existing task for the document.</p>



<h3 id="flag-new-doc">Using the Intent flag to add a task</h3>



<p>When you create a new document for your activity, you call the

{@link android.app.ActivityManager.AppTask#startActivity(android.content.Context, android.content.Intent, android.os.Bundle) startActivity()}

method of the {@link android.app.ActivityManager.AppTask} class, passing to it the intent that

launches the activity. To insert a logical break so that the system treats your activity as a new

task in the overview screen, pass the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT} flag

in the {@link android.content.Intent#addFlags(int) addFlags()} method of the {@link android.content.Intent}

that launches the activity.</p>



<p class="note"><strong>Note:</strong> The {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT}

flag replaces the {@link android.content.Intent#FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET} flag,

which is deprecated as of Android 5.0 (API level 21).</p>



<p>If you set the {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flag when you create

the new document, the system always creates a new task with the target activity as the root.

This setting allows the same document to be opened in more than one task. The following code demonstrates

how the main activity does this:</p>



<p class="code-caption"><a href="{@docRoot}samples/activitytasks/src/com/example/android/documentcentricrecents/DocumentCentricActivity.html">

DocumentCentricActivity.java</a></p>

<pre>

public void createNewDocument(View view) {

      final Intent newDocumentIntent = newDocumentIntent();

      if (useMultipleTasks) {

          newDocumentIntent.addFlags(Intent.FLAG_ACTIVITY_MULTIPLE_TASK);

      }

      startActivity(newDocumentIntent);

  }



  private Intent newDocumentIntent() {

      boolean useMultipleTasks = mCheckbox.isChecked();

      final Intent newDocumentIntent = new Intent(this, NewDocumentActivity.class);

      newDocumentIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_DOCUMENT);

      newDocumentIntent.putExtra(KEY_EXTRA_NEW_DOCUMENT_COUNTER, incrementAndGet());

      return newDocumentIntent;

  }



  private static int incrementAndGet() {

      Log.d(TAG, "incrementAndGet(): " + mDocumentCounter);

      return mDocumentCounter++;

  }

}

</pre>



<p class="note"><strong>Note:</strong> Activities launched with the {@code FLAG_ACTIVITY_NEW_DOCUMENT}

flag must have the {@code android:launchMode="standard"} attribute value (the default) set in the

manifest.</p>



<p>When the main activity launches a new activity, the system searches through existing tasks for

one whose intent matches the intent component name and the Intent data for the activity. If the task

is not found, or the intent contained the {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK}

flag, a new task will be created with the activity as its root. If it finds one, it brings that task

to the front and passes the new intent to {@link android.app.Activity#onNewIntent onNewIntent()}.

The new activity gets the intent and creates a new document in the overview screen, as in the

following example:</p>



<p class="code-caption"><a href="{@docRoot}samples/activitytasks/src/com/example/android/documentcentricrecents/NewDocumentActivity.html">

NewDocumentActivity.java</a></p>

<pre>

&#64;Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_new_document);

    mDocumentCount = getIntent()

            .getIntExtra(DocumentCentricActivity.KEY_EXTRA_NEW_DOCUMENT_COUNTER, 0);

    mDocumentCounterTextView = (TextView) findViewById(

            R.id.hello_new_document_text_view);

    setDocumentCounterText(R.string.hello_new_document_counter);

}



&#64;Override

protected void onNewIntent(Intent intent) {

    super.onNewIntent(intent);

    /* If FLAG_ACTIVITY_MULTIPLE_TASK has not been used, this activity

    is reused to create a new document.

     */

    setDocumentCounterText(R.string.reusing_document_counter);

}

</pre>





<h3 id="#attr-doclaunch">Using the activity attribute to add a task</h3>



<p>An activity can also specify in its manifest that it always launches into a new task by using

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

attribute, <a href="{@docRoot}guide/topics/manifest/activity-element.html#dlmode">

{@code android:documentLaunchMode}</a>. This attribute has four values which produce the following

effects when the user opens a document with the application:</p>



<dl>

  <dt>"{@code intoExisting}"</dt>

  <dd>The activity reuses an existing task for the document. This is the same as setting the

  {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT} flag <em>without</em> setting the

  {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flag, as described in

  <a href="#flag-new-doc">Using the Intent flag to add a task</a>, above.</dd>



  <dt>"{@code always}"</dt>

  <dd>The activity creates a new task for the document, even if the document is already opened. Using

  this value is the same as setting both the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT}

  and {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flags.</dd>



  <dt>"{@code none”}"</dt>

  <dd>The activity does not create a new task for the document. The overview screen treats the

  activity as it would by default: it displays a single task for the app, which

  resumes from whatever activity the user last invoked.</dd>



  <dt>"{@code never}"</dt>

  <dd>The activity does not create a new task for the document. Setting this value overrides the

  behavior of the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT}

  and {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flags, if either of these are set

  in the intent, and the overview screen displays a single task for the app, which resumes from

  whatever activity the user last invoked.</dd>

</dl>



<p class="note"><strong>Note:</strong> For values other than {@code none} and {@code never} the

activity must be defined with {@code launchMode="standard"}. If this attribute is not specified,

{@code documentLaunchMode="none"} is used.</p>



<h2 id="removing">Removing Tasks</h2>



<p>By default a document task is automatically removed from the overview screen when its activity

finishes. You can override this behavior with the {@link android.app.ActivityManager.AppTask} class,

with an {@link android.content.Intent} flag, or with an<code><a href="{@docRoot}guide/topics/manifest/activity-element.html">

&lt;activity&gt;</a></code> attribute.</p>



<p>You can always exclude a task from the overview screen entirely by setting the

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

attribute, <a href="{@docRoot}guide/topics/manifest/activity-element.html#exclude">

{@code android:excludeFromRecents}</a> to {@code true}.</p>



<p>You can set the maximum number of tasks that your app can include in the overview screen by setting

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

attribute <a href="{@docRoot}guide/topics/manifest/activity-element.html#maxrecents">{@code android:maxRecents}

</a> to an integer value. The default is 16. When the maximum number of tasks is reached, the least

recently used task is removed from the overview screen. The {@code android:maxRecents} maximum value

is 50 (25 on low memory devices); values less than 1 are not valid.</p>



<h3 id="#apptask-remove">Using the AppTask class to remove tasks</h3>



<p>In the activity that creates a new task in the overview screen, you can

specify when to remove the task and finish all activities associated with it by calling

the {@link android.app.ActivityManager.AppTask#finishAndRemoveTask() finishAndRemoveTask()} method.</p>



<p class="code-caption"><a href="{@docRoot}samples/activitytasks/index.html">

NewDocumentActivity.java</a></p>

<pre>

public void onRemoveFromRecents(View view) {

    // The document is no longer needed; remove its task.

    finishAndRemoveTask();

}

</pre>



<p class="note"><strong>Note:</strong> Using the

{@link android.app.ActivityManager.AppTask#finishAndRemoveTask() finishAndRemoveTask()} method

overrides the use of the {@link android.content.Intent#FLAG_ACTIVITY_RETAIN_IN_RECENTS} tag,

discussed below.</p>



<h3 id="#retain-finished">Retaining finished tasks</h3>



<p>If you want to retain a task in the overview screen, even if its activity has finished, pass

the {@link android.content.Intent#FLAG_ACTIVITY_RETAIN_IN_RECENTS} flag in the

{@link android.content.Intent#addFlags(int) addFlags()} method of the Intent that launches the activity.</p>



<p class="code-caption"><a href="{@docRoot}samples/activitytasks/src/com/example/android/documentcentricrecents/DocumentCentricActivity.html">

DocumentCentricActivity.java</a></p>

<pre>

private Intent newDocumentIntent() {

    final Intent newDocumentIntent = new Intent(this, NewDocumentActivity.class);

    newDocumentIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_DOCUMENT |

      android.content.Intent.FLAG_ACTIVITY_RETAIN_IN_RECENTS);

    newDocumentIntent.putExtra(KEY_EXTRA_NEW_DOCUMENT_COUNTER, incrementAndGet());

    return newDocumentIntent;

}

</pre>



<p>To achieve the same effect, set the

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

attribute <a href="{@docRoot}guide/topics/manifest/activity-element.html#autoremrecents">

{@code android:autoRemoveFromRecents}</a> to {@code false}. The default value is {@code true}

for document activities, and {@code false} for regular activities. Using this attribute overrides

the {@link android.content.Intent#FLAG_ACTIVITY_RETAIN_IN_RECENTS} flag, discussed previously.</p>

docs/html/guide/components/tasks-and-back-stack.jd

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docs/html/guide/guide_toc.cs

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@@ -55,6 +55,9 @@ 
          <li><a href="<?cs var:toroot ?>guide/components/tasks-and-back-stack.html">

              <span class="en">Tasks and Back Stack</span>

            </a></li>

          <li><a href="<?cs var:toroot ?>guide/components/recents.html">

              <span class="en">Overview Screen</span>

            </a></li>

        </ul>

      </li>

      <li class="nav-section">

docs/html/guide/topics/manifest/activity-element.jd

+92 −9
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@@ -8,11 +8,14 @@ parent.link=manifest-intro.html 
<dd><pre class="stx">&lt;activity android:<a href="#embedded">allowEmbedded</a>=["true" | "false"]

          android:<a href="#reparent">allowTaskReparenting</a>=["true" | "false"]

          android:<a href="#always">alwaysRetainTaskState</a>=["true" | "false"]

          android:<a href="#autoremrecents">autoRemoveFromRecents</a>=["true" | "false"]

          android:<a href="#clear">clearTaskOnLaunch</a>=["true" | "false"]

          android:<a href="#config">configChanges</a>=["mcc", "mnc", "locale",

                                 "touchscreen", "keyboard", "keyboardHidden",

                                 "navigation", "screenLayout", "fontScale", "uiMode",

                                 "orientation", "screenSize", "smallestScreenSize"]

          android:<a href="#dlmode">documentLaunchMode</a>=["intoExisting", "always",

                                  "none", "never"]

          android:<a href="#enabled">enabled</a>=["true" | "false"]

          android:<a href="#exclude">excludeFromRecents</a>=["true" | "false"]

          android:<a href="#exported">exported</a>=["true" | "false"]
@@ -22,12 +25,14 @@ parent.link=manifest-intro.html 
          android:<a href="#label">label</a>="<i>string resource</i>"

          android:<a href="#lmode">launchMode</a>=["multiple" | "singleTop" |

                              "singleTask" | "singleInstance"]

          android:<a href="#maxRecents">maxRecents</a>="<i>integer</i>"

          android:<a href="#multi">multiprocess</a>=["true" | "false"]

          android:<a href="#nm">name</a>="<i>string</i>"

          android:<a href="#nohist">noHistory</a>=["true" | "false"]  <!-- ##api level 3## -->

          android:<a href="#parent">parentActivityName</a>="<i>string</i>" <!-- api level 16 -->

          android:<a href="#prmsn">permission</a>="<i>string</i>"

          android:<a href="#proc">process</a>="<i>string</i>"

          android:<a href="#relinquish">relinquishTaskIdentity</a>=["true" | "false"]

          android:<a href="#screen">screenOrientation</a>=["unspecified" | "behind" |

                                     "landscape" | "portrait" |

                                     "reverseLandscape" | "reversePortrait" |
@@ -139,6 +144,15 @@ useful, for example, in an application like the web browser where there is 
a lot of state (such as multiple open tabs) that users would not like to lose.

</p></dd>



<dt><a name="autoremrecents"></a>{@code android:autoRemoveFromRecents}</dt>

<dd>Whether or not tasks launched by activities with this attribute remains in the

<a href="{@docRoot}guide/components/recents.html">overview screen</a> until the last activity in the

task is completed. If {@code true}, the task is

automatically removed from the overview screen. This overrides the caller's use of

{@link android.content.Intent#FLAG_ACTIVITY_RETAIN_IN_RECENTS}. It must be a boolean value, either

"{@code true}" or "{@code false}".</dd>





<dt><a name="clear"></a>{@code android:clearTaskOnLaunch}</dt>

<dd>Whether or not all activities will be removed from the task, except for

the root activity, whenever it is re-launched from the home screen &mdash;
@@ -177,7 +191,7 @@ as described above. 
<dd>Lists configuration changes that the activity will handle itself.  When a configuration

change occurs at runtime, the activity is shut down and restarted by default, but declaring a

configuration with this attribute will prevent the activity from being restarted. Instead, the

activity remains running and its <code>{@link android.app.Activity#onConfigurationChanged

activity remains running and its <code>{@link android.app.Activity#onConfigurationChanged(android.content.res.Configuration)

onConfigurationChanged()}</code> method is called.



<p class="note"><strong>Note:</strong> Using this attribute should be
@@ -271,20 +285,67 @@ restart your activity, even when running on an Android 3.2 or higher device). 


<p>

All of these configuration changes can impact the resource values seen by the

application.  Therefore, when <code>{@link android.app.Activity#onConfigurationChanged

application.  Therefore, when <code>{@link android.app.Activity#onConfigurationChanged(android.content.res.Configuration)

onConfigurationChanged()}</code> is called, it will generally be necessary to again

retrieve all resources (including view layouts, drawables, and so on) to correctly

handle the change.

</p></dd>



<dt><a name="dlmode"></a>{@code android:documentLaunchMode}</dt>

<dd>Specifies how a new instance of an activity should be added to a task each time it is

launched. This attribute permits the user to have multiple documents from the same application

appear in the <a href="{@docRoot}guide/components/recents.html">overview screen</a>.



<p>This attribute has four values which produce the following effects when the user opens a document

with the application:</p>



<table>

<tr>

  <th>Value</th>

  <th>Description</th>

</tr><tr>

  <td>"{@code intoExisting}"</td>

  <td>The activity reuses the existing task for the document. Using this value is the same as setting

  the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT} flag, <em>without</em> setting the

  {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flag, as described in

  <a href="{@docRoot}guide/components/recents.html#flag-new-doc">Using the Intent flag to add a task

  </a>.</td>

</tr><tr>

    <td>"{@code always}"</td>

    <td>The activity creates a new task for the document, even if the document is already opened.

    This is the same as setting both the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT}

    and {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flags.</td>

</tr><tr>

    <td>"{@code none}"</td>

    <td>The activity does not create a new task for the activity. This is the default value, which

    creates a new task only when {@link android.content.Intent#FLAG_ACTIVITY_NEW_TASK} is set.

    The overview screen treats the activity as it would by default: it displays a single task for

    the app, which resumes from whatever activity the user last invoked.</td>

</tr><tr>

    <td>"{@code never}"</td>

    <td>This activity is not launched into a new document even if the Intent contains

    {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT}. Setting this overrides the behavior

    of the {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT} and

    {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK} flags, if either of these are set in

    the activity, and the overview screen displays a single task for the app, which resumes from

    whatever activity the user last invoked.</td>

</tr>

</table>



<p class="note"><strong>Note:</strong> For values other than "{@code none}" and "{@code never}" the

activity must be defined with {@code launchMode="standard"}. If this attribute is not specified,

{@code documentLaunchMode="none"} is used.</p>

</dd>



<dt><a name="enabled"></a>{@code android:enabled}</dt>

<dd>Whether or not the activity can be instantiated by the system &mdash;

"{@code true}" if it can be, and "{@code false}" if not.  The default value

{@code "true"} if it can be, and "{@code false}" if not.  The default value

is "{@code true}".



<p>

The <code><a href="{@docRoot}guide/topics/manifest/application-element.html">&lt;application&gt;</a></code> element has its own

<code><a href="{@docRoot}guide/topics/manifest/application-element.html#enabled">enabled</a></code>

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

</code> element has its own<code>

<a href="{@docRoot}guide/topics/manifest/application-element.html#enabled">enabled</a></code>

attribute that applies to all application components, including activities.  The

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

and {@code &lt;activity&gt;} attributes must both be "{@code true}" (as they both
@@ -294,10 +355,11 @@ is "{@code false}", it cannot be instantiated. 


<dt><a name="exclude"></a>{@code android:excludeFromRecents}</dt>

<dd>Whether or not the task initiated by this activity should be excluded from the list of recently

used applications ("recent apps"). That is, when this activity is the root activity of a new task,

this attribute determines whether the task should not appear in the list of recent apps. Set "{@code

true}" if the task should be <em>excluded</em> from the list; set "{@code false}" if it should be

<em>included</em>. The default value is "{@code false}".

used applications, the <a href="{@docRoot}guide/components/recents.html">

overview screen</a>. That is, when this activity is the root activity of a new

task, this attribute determines whether the task should not appear in the list of recent apps. Set

"{@code true}" if the task should be <em>excluded</em> from the list; set "{@code false}" if it

should be <em>included</em>. The default value is "{@code false}".

</p></dd>



<dt><a name="exported"></a>{@code android:exported}</dt>
@@ -550,6 +612,13 @@ document. 
</p>

</dd>



<dt><a name="maxrecents"></a>{@code android:maxRecents}</dt>

<dd>The maximum number of tasks rooted at this activity in the <a href="{@docRoot}guide/components/recents.html">

overview screen</a>. When this number of entries is reached, the system removes the least-recently

used instance from the overview screen. Valid values are 1 through 50 (25 on low memory devices);

zero is invalid. This must be an integer value, such as 50. The default value is 16.

</dd>



<dt><a name="multi"></a>{@code android:multiprocess}</dt>

<dd>Whether an instance of the activity can be launched into the process of the component

that started it &mdash; "{@code true}" if it can be, and "{@code false}" if not.
@@ -685,6 +754,20 @@ resource usage. 
attribute can set a different default process name for all components.

</dd>



<dt><a name="relinquish"></a>{@code android:relinquishTaskIdentity}</dt>

<dd>Whether or not the activity relinquishes its task identifiers to an activity above it in the

task stack. A task whose root activity has this attribute set to "{@code true}" replaces the base

Intent with that of the next activity in the task. If the next activity also has this attribute set

to "{@code true}" then it will yield the base Intent to any activity that it launches in the same

task. This continues for each activity until an activity is encountered which has this attribute set

to "{@code false}". The default value is "{@code false}".



<p>This attribute set to "{@code true}" also permits the activity's use of the

{@link android.app.ActivityManager.TaskDescription} to change labels, colors

and icons in the <a href="{@docRoot}guide/components/recents.html">overview screen</a>.</p>

</dd>





<dt><a name="screen"></a>{@code android:screenOrientation}</dt>

<dd>The orientation of the activity's display on the device.

docs/html/images/components/recents.png

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