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

page.title=
parent.title=
parent.link=activities.html
@jd:body

<div id="qv-wrapper">
<div id="qv">

<h2></h2>
<ol>
<li><a href="#ActivityState"></a></li></li>
<li><a href="#ManagingTasks"></a>
  <ol>
    <li><a href="#TaskLaunchModes"></a></li>
    <li><a href="#Affinities"></a></li>
    <li><a href="#Clearing"></a></li>
    <li><a href="#Starting"></a></li>
  </ol>
</li>
</ol>

<h2></h2>
<ol>
  <li><a href="http://android-developers.blogspot.com/2010/04/multitasking-android-way.html">Multitasking the Android Way</a>
</li>
</ol>

<h2></h2>
<ol>
  <li><a href="{@docRoot}design/patterns/navigation.html">Android Design: Navigation</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html">{@code &lt;activity&gt;} manifest element</a>
</li>
  <li><a href="{@docRoot}guide/components/recents.html"></a></li>
</ol>
</div>
</div>


<p><a href="{@docRoot}guide/components/activities.html"></a>

  1
</p>

<p>


Android <em></em>

</p>

<p>
<em></em>
</p>

<!-- SAVE FOR WHEN THE FRAGMENT DOC IS ADDED
<div class="sidebox-wrapper">
<div class="sidebox">
<h3>Adding fragments to a task's back stack</h3>

<p>Your activity can also include {@link android.app.Fragment}s to the back stack. For example,
suppose you have a two-pane layout using fragments, one of which is a list view (fragment A) and the
other being a layout to display an item from the list (fragment B). When the user selects an item
from the list, fragment B is replaced by a new fragment (fragment C). In this case, it might be
desireable for the user to navigate back to reveal fragment B, using the <em>Back</em> button.</p>
<p>In order to add fragment B to the back stack so that this is possible, you must call {@link
android.app.FragmentTransaction#addToBackStack addToBackStack()} before you {@link
android.app.FragmentTransaction#commit()} the transaction that replaces fragment B with fragment
C.</p>
<p>For more information about using fragments and adding them to the back stack, see the {@link
android.app.Fragment} class documentation.</p>

</div>
</div>
-->

<p>


</p>

<p>

 [<em></em>] UI


 &mdash;  [<em></em>]


 1

</p>

<img src="{@docRoot}images/fundamentals/diagram_backstack.png" alt="" />
<p class="img-caption"><strong> 1.</strong>
 [<em></em>]

</p>


<p> [<em></em>]


</p>

<div class="figure" style="width:287px">
<img src="{@docRoot}images/fundamentals/diagram_multitasking.png" alt="" /> <p
class="img-caption"><strong> 2.</strong> 2 :  B  A
</p>
</div>
<div class="figure" style="width:215px">
  <img src="{@docRoot}images/fundamentals/diagram_multiple_instances.png" alt="" /> <p
class="img-caption"><strong> 3.</strong> 1 </p>
</div>

<p> [<em></em>]
 &mdash;  2


 A 3  2
 [<em></em>]

 A
 B B
 A  A  &mdash; 3


 B <a href="{@docRoot}guide/components/recents.html"></a> B Android


</p>

<p class="note"><strong>:</strong>   <a href="#ActivityState"></a>


</p>

<p>


 3  1
 [<em></em>] UI


1
<a href="#ManagingTasks"></a></p>


<p></p>

<ul>
  <li> A  B  A  B  [<em></em>]  A


</li>
  <li> [<em></em>]


</li>
  <li> [<em></em>]

<em></em>
</li>
  <li></li>
</ul>


<div class="note design">
<p><strong> </strong></p>
  <p>Android  Android Design <a href="{@docRoot}design/patterns/navigation.html">Navigation</a></p>
</div>


<h2 id="ActivityState"></h2>

<p>

 <strong></strong>

</p>

<p> 1


{@link android.app.Activity#onSaveInstanceState onSaveInstanceState()}


</p>

<p><a href="{@docRoot}guide/components/activities.html#SavingActivityState">Activities</a>
</p>


<h2 id="ManagingTasks"></h2>

<p>Android


</p>

<p><a href="{@docRoot}guide/topics/manifest/activity-element.html">{@code &lt;activity&gt;}</a>   {@link android.app.Activity#startActivity startActivity()}


</p>

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

<ul class="nolist">
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#aff">  {@code taskAffinity}</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">  {@code launchMode}</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#reparent">  {@code allowTaskReparenting}</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#clear">  {@code clearTaskOnLaunch}</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#always">  {@code alwaysRetainTaskState}</a>
</li>
  <li><a href="{@docRoot}guide/topics/manifest/activity-element.html#finish">  {@code finishOnTaskLaunch}</a>
</li>
</ul>

<p> </p>

<ul class="nolist">
  <li>{@link android.content.Intent#FLAG_ACTIVITY_NEW_TASK}</li>
  <li>{@link android.content.Intent#FLAG_ACTIVITY_CLEAR_TOP}</li>
  <li>{@link android.content.Intent#FLAG_ACTIVITY_SINGLE_TOP}</li>
</ul>

<p>
</p>

<p>
<a href="{@docRoot}guide/components/recents.html"></a>

</p>

<p class="caution"><strong>:</strong>
 [<em></em>]


</p>


<h3 id="TaskLaunchModes"></h3>

<p>
 2 </p>
<ul class="nolist">
  <li><a href="#ManifestForTasks"> </a>
    <p>
</li>
  <li><a href="#IntentFlagsForTasks"> </a>
    <p>{@link android.app.Activity#startActivity startActivity()}  {@link android.content.Intent}

</p></li>
</ul>

<p> A  B  B  A  B

 B  B  A

</p>

<p class="note"><strong>:</strong>

</p>


<h4 id="ManifestForTasks"> </h4>

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


</p>

<p><a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">{@code launchMode}</a>

<code><a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">launchMode</a></code>  4

</p>

<dl>
<dt>{@code "standard"}</dt>
  <dd>
1
</dd>
<dt>{@code "singleTop"}</dt>
  <dd>{@link android.app.Activity#onNewIntent onNewIntent()}


1 <em></em>


  <p> BC D   A  A-B-C-D  D
D  D  {@code "standard"}  A-B-C-D-D D  {@code "singleTop"}  D  {@link android.app.Activity#onNewIntent onNewIntent()}  &mdash;  A-B-C-D B  {@code "singleTop"} B


</p>
  <p class="note"><strong>:</strong>  [<em></em>]
 {@link android.app.Activity#onNewIntent onNewIntent()}  [<em></em>]


</p>
</dd>

<dt>{@code "singleTask"}</dt>
  <dd>{@link android.app.Activity#onNewIntent onNewIntent()}


 1

  <p class="note"><strong>:</strong>  [<em></em>]
</p></dd>
<dt>{@code "singleInstance"}</dt>
  <dd> {@code "singleTask"}

</dd>
</dl>


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


Android Browser Android Browser

</p>

<p> [<em></em>]
{@code singleTask}


 4 </p>

<img src="{@docRoot}images/fundamentals/diagram_backstack_singletask_multiactivity.png" alt="" />
<p class="img-caption"><strong> 4.</strong>singleTask


</p>

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


</p>

<p class="note"><strong>:</strong> <a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">{@code launchMode}</a>

</p>


<h4 id="#IntentFlagsForTasks"> </h4>

<p>{@link android.app.Activity#startActivity startActivity()}


</p>

<p>
  <dt>{@link android.content.Intent#FLAG_ACTIVITY_NEW_TASK}</dt>
    <dd> {@link android.app.Activity#onNewIntent onNewIntent()}


    <p> {@code "singleTask"} <a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">{@code launchMode}</a>
</p></dd>
  <dt>{@link android.content.Intent#FLAG_ACTIVITY_SINGLE_TOP}</dt>
    <dd> {@link android.app.Activity#onNewIntent onNewIntent()}


    <p> {@code "singleTop"} <a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">{@code launchMode}</a>
</p></dd>
  <dt>{@link android.content.Intent#FLAG_ACTIVITY_CLEAR_TOP}</dt>
    <dd>{@link android.app.Activity#onNewIntent onNewIntent()}


    <p> <a href="{@docRoot}guide/topics/manifest/activity-element.html#lmode">{@code launchMode}</a>
</p>
    <p> {@code FLAG_ACTIVITY_CLEAR_TOP}  {@code FLAG_ACTIVITY_NEW_TASK}


 </p>
    <p class="note"><strong>:</strong>  {@code "standard"}


 {@code "standard"}
 </p>
</dd>
</dl>


<h3 id="Affinities"></h3>

<p><em></em>


</p>

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

</p>

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


</p>

<p> 2 </p>
<ul>
  <li> {@link android.content.Intent#FLAG_ACTIVITY_NEW_TASK}


<p>{@link android.app.Activity#startActivity startActivity()}

{@link android.app.Activity#startActivity startActivity()}  {@link android.content.Intent#FLAG_ACTIVITY_NEW_TASK}


</p>

<p> [<em></em>]

 {@link android.app.Activity#startActivity startActivity()}  {@code FLAG_ACTIVITY_NEW_TASK}   {@link android.content.Intent#CATEGORY_LAUNCHER}  <a href="#Starting"></a>


</p>
</li>

  <li> <a href="{@docRoot}guide/topics/manifest/activity-element.html#reparent">{@code allowTaskReparenting}</a>  {@code "true"}

  <p>
</p>
  <p>


</p>
</li>
</ul>

<p class="note"><strong>:</strong> {@code .apk}  1  <a href="{@docRoot}guide/topics/manifest/activity-element.html#aff">{@code taskAffinity}</a>

</p>


<h3 id="Clearing"></h3>

<p>


 </p>

<p> </p>

<dl>
<dt><code><a
href="{@docRoot}guide/topics/manifest/activity-element.html#always">alwaysRetainTaskState</a></code>
</dt>
<dd>  {@code "true"}

</dd>

<dt><code><a
href="{@docRoot}guide/topics/manifest/activity-element.html#clear">clearTaskOnLaunch</a></code></dt>
<dd>  {@code "true"}

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


</dd>

<dt><code><a
href="{@docRoot}guide/topics/manifest/activity-element.html#finish">finishOnTaskLaunch</a></code>
</dt>
<dd><a href="{@docRoot}guide/topics/manifest/activity-element.html#clear">{@code clearTaskOnLaunch}</a>  1


 {@code "true"}

</dd>
</dl>


<h3 id="Starting"></h3>

<p> {@code "android.intent.action.MAIN"} {@code "android.intent.category.LAUNCHER"}


</p>

<pre>
&lt;activity ... &gt;
    &lt;intent-filter ... &gt;
        &lt;action android:name="android.intent.action.MAIN" /&gt;
        &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
    &lt;/intent-filter&gt;
    ...
&lt;/activity&gt;
</pre>

<p>


</p>

<p> 2
 {@link android.content.Intent#ACTION_MAIN}  {@link android.content.Intent#CATEGORY_LAUNCHER}  {@code "singleTask"}  {@code "singleInstance"}  2 <a href="#LaunchModes"></a>


 {@code "singleTask"}
 [<em></em>]

</p>

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


</p>

<p><a href="{@docRoot}guide/components/recents.html"></a>

</p>

<!--
<h2>Beginner's Path</h2>

<p>For more information about how to use intents to
activate other application components and publish the intents to which your components
respond, continue with the <b><a
href="{@docRoot}guide/components/intents-filters.html">Intents and Intent
Filters</a></b> document.</p>
-->