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page.title=Implementing Ancestral Navigation
parent.title=Implementing Effective Navigation
parent.link=index.html
trainingnavtop=true
previous.title=Implementing Lateral Navigation
previous.link=lateral.html
next.title=Implementing Temporal Navigation
next.link=temporal.html
@jd:body
<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to:</h2>
<ol>
<li><a href="#up">Implement <em>Up</em> Navigation</a></li>
<li><a href="#app-home">Properly Handle the Application Home Screen</a></li>
</ol>
<h2>You should also read</h2>
<ul>
<li><a href="{@docRoot}training/design-navigation/ancestral-temporal.html">Providing Ancestral and Temporal Navigation</a></li>
<li><a href="{@docRoot}guide/components/tasks-and-back-stack.html">Tasks and Back Stack</a></li>
<li><a href="{@docRoot}design/patterns/navigation.html">Android Design: Navigation</a></li>
</ul>
<h2>Try it out</h2>
<div class="download-box">
<a href="http://developer.android.com/shareables/training/EffectiveNavigation.zip"
class="button">Download the sample app</a>
<p class="filename">EffectiveNavigation.zip</p>
</div>
</div>
</div>
<p><em>Ancestral navigation</em> is up the application's information hierarchy, where the top of the hierarchy (or root) is the application's home screen. This navigation concept is described in <a href="{@docRoot}training/design-navigation/ancestral-temporal.html">Designing Effective Navigation</a>. This lesson discusses how to provide ancestral navigation using the <em>Up</em> button in the action bar.</p>
<h2 id="up">Implement <em>Up</em> Navigation</h2>
<p>When implementing ancestral navigation, all screens in your application that aren't the home screen should offer a means of navigating to the immediate parent screen in the hierarchy via the <em>Up</em> button in the action bar.</p>
<img src="{@docRoot}images/training/implementing-navigation-up.png"
alt="The Up button in the action bar." id="figure-up">
<p class="img-caption"><strong>Figure 1.</strong> The <em>Up</em> button in the action bar.</p>
<p>Regardless of how the current screen was reached, pressing this button should always take the user to the same screen in the hierarchy.</p>
<p>To implement <em>Up</em>, enable it in the action bar in your activity's {@link android.app.Activity#onCreate onCreate()} method:</p>
<pre>
{@literal @}Override
public void onCreate(Bundle savedInstanceState) {
...
getActionBar().setDisplayHomeAsUpEnabled(true);
...
}
</pre>
<p>You should also handle <code>android.R.id.home</code> in {@link android.app.Activity#onOptionsItemSelected onOptionsItemSelected()}. This resource is the menu item ID for the <em>Home</em> (or <em>Up</em>) button. To ensure that a specific parent activity is shown, <em>DO NOT</em> simply call {@link android.app.Activity#finish finish()}. Instead, use an intent such as the one described below.</p>
<pre>
{@literal @}Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This is called when the Home (Up) button is pressed
// in the Action Bar.
Intent parentActivityIntent = new Intent(this, MyParentActivity.class);
parentActivityIntent.addFlags(
Intent.FLAG_ACTIVITY_CLEAR_TOP |
Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(parentActivityIntent);
finish();
return true;
}
return super.onOptionsItemSelected(item);
}
</pre>
<p>When the current activity belongs to a task from a different application—for example if it was reached via an intent from another application—pressing <em>Up</em> should create a new task for the application with a synthesized back stack. This approach is described in <a href="{@docRoot}design/patterns/navigation.html">Android Design: Navigation</a> and the {@link android.support.v4.app.TaskStackBuilder} class reference.</p>
<p>The {@link android.support.v4.app.NavUtils} and {@link android.support.v4.app.TaskStackBuilder} classes in the <a href="{@docRoot}tools/extras/support-library.html">Android Support Package</a> provide helpers for implementing this behavior correctly. An example usage of these two helper classes is below:</p>
<pre>
{@literal @}Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
Intent upIntent = new Intent(this, MyParentActivity.class);
if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
// This activity is not part of the application's task, so create a new task
// with a synthesized back stack.
TaskStackBuilder.from(this)
.addNextIntent(new Intent(this, MyGreatGrandParentActivity.class))
.addNextIntent(new Intent(this, MyGrandParentActivity.class))
.addNextIntent(upIntent)
.startActivities();
finish();
} else {
// This activity is part of the application's task, so simply
// navigate up to the hierarchical parent activity.
NavUtils.navigateUpTo(this, upIntent);
}
return true;
}
return super.onOptionsItemSelected(item);
}
</pre>
<h2 id="app-home">Properly Handle the Application Home Screen</h2>
<p>By default, the <em>Home</em> button in the action bar is interactive. Since it does not make much sense to navigate home—or up one level—while on the home screen, you should disable the button like so:</p>
<pre>
getActionBar().setHomeButtonEnabled(false);
</pre>
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