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am 4f832bc7: am 3b1c5d55: add tip about including android:id for layout state

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* commit '4f832bc796bad90e5632c3ab69e305b3c7c008ba':
  add tip about including android:id for layout state
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Scott Main
2012-09-25 19:05:35 -07:00
committed by Android Git Automerger
parent c80188ebef 4f832bc796
commit 82e7fdfd47
1 changed files with 16 additions and 11 deletions
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27
docs/html/training/basics/activity-lifecycle/recreating.jd
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@@ -54,20 +54,25 @@ load alternative resources (such as the layout).</p>
<p>By default, the system uses the {@link android.os.Bundle} instance state to save information
about each {@link android.view.View} object in your activity layout (such as the text value entered
into an {@link android.widget.EditText} object). So, if your activity instance is destroyed and
recreated, the state of the layout is automatically restored to its previous state. However, your
recreated, the state of the layout is restored to its previous state with no
code required by you. However, your
activity might have more state information that you'd like to restore, such as member variables that
track the user's progress in the activity.</p>
<p>In order for you to add additional data to the saved instance state for your activity, there's an
additional callback method in the activity lifecycle that's not shown in the illustration from
previous lessons. The method is {@link android.app.Activity#onSaveInstanceState
onSaveInstanceState()} and the system calls it when the user is leaving your activity. When the
system calls this method, it passes the {@link android.os.Bundle} object that will be saved in the
event that your activity is destroyed unexpectedly so you can add additional information to it. Then
if the system must recreate the activity instance after it was destroyed, it passes the same {@link
android.os.Bundle} object to your activity's {@link android.app.Activity#onRestoreInstanceState
onRestoreInstanceState()} method and also to your {@link android.app.Activity#onCreate onCreate()}
method.</p>
<p class="note"><strong>Note:</strong> In order for the Android system to restore the state of
the views in your activity, <strong>each view must have a unique ID</strong>, supplied by the
<a href="{@docRoot}reference/android/view/View.html#attr_android:id">{@code
android:id}</a> attribute.</p>
<p>To save additional data about the activity state, you must override
the {@link android.app.Activity#onSaveInstanceState onSaveInstanceState()} callback method.
The system calls this method when the user is leaving your activity
and passes it the {@link android.os.Bundle} object that will be saved in the
event that your activity is destroyed unexpectedly. If
the system must recreate the activity instance later, it passes the same {@link
android.os.Bundle} object to both the {@link android.app.Activity#onRestoreInstanceState
onRestoreInstanceState()} and {@link android.app.Activity#onCreate onCreate()}
methods.</p>
<img src="{@docRoot}images/training/basics/basic-lifecycle-savestate.png" />
<p class="img-caption"><strong>Figure 2.</strong> As the system begins to stop your activity, it