docs/html/guide/topics/data/autobackup.jd

page.title=Auto Backup for Apps
page.tags=backup, marshmallow, androidm
page.keywords=backup, autobackup
page.image=images/cards/card-auto-backup_2x.png

@jd:body

<div id="qv-wrapper">
<div id="qv">
  <h2>In this document</h2>
  <ol>
    <li><a href="#Files">Files that are backed up</a></li>
    <li><a href="#BackupLocation">Backup location</a></li>
    <li><a href="#BackupSchedule">Backup schedule</a></li>
    <li><a href="#RestoreSchedule">Restore schedule</a></li>
    <li><a href="#EnablingAutoBackup">Enabling and disabling Auto Backup</a></li>
    <li><a href="#IncludingFiles">Including and excluding files</a><ul>
      <li><a href="#XMLSyntax">XML config syntax</a></li>
    </ul></li>
    <li><a href="#ImplementingBackupAgent">Implementing BackupAgent</a></li>
  </ol>

  <h2>Key classes</h2>
  <ol>
    <li>{@link android.app.backup.BackupAgent}</li>
    <li><a href="{@docRoot}reference/android/R.attr.html">R.attr</a></li>
  </ol>

</div>
</div>

Since Android 6.0 (API 23), Android has offered the <em>Auto Backup for Apps</em> feature as
a way for developers to quickly add backup functionality to their apps. Auto
Backup preserves app data by uploading it to the user’s Google Drive account.
The amount of data is limited to 25MB per user of your app and there is no
charge for storing backup data.

<h2 id="Files">Files that are backed up</h2>
<p>By default, Auto Backup includes files in most of the directories that are
assigned to your app by the system:
<ul>
  <li>Shared preferences files.
  <li>Files in the directory returned by {@link android.content.Context#getFilesDir()}.
  <li>Files in the directory returned by {@link android.content.Context#getDatabasePath(String)},
    which also includes files created with the
    {@link android.database.sqlite.SQLiteOpenHelper} class.
  <li>Files in directories created with {@link android.content.Context#getDir(String,int)}.
  <li>Files on external storage in the directory returned by
    {@link android.content.Context#getExternalFilesDir(String)}.</li></ul>

<p>Auto Backup excludes files in directories returned by
  {@link android.content.Context#getCacheDir()},
  {@link android.content.Context#getCodeCacheDir()}, or
  {@link android.content.Context#getNoBackupFilesDir()}. The files saved
  in these locations are only needed temporarily, or are intentionally
  excluded from backup operations.

<p>You can configure your app to include and exclude particular files.
For more information, see the <a href="#IncludingFiles">Include and exclude files</a>
section.

<h2 id="BackupLocation">Backup location</h2>
<p>Backup data is stored in a private folder in the user's Google Drive account,
limited to 25MB per app. The saved data does not count towards the user's
personal Google Drive quota. Only the most recent backup is stored. When a
backup is made, the previous backup (if one exists) is deleted.

<p>Users can see a list of apps that have been backed up in the Google Drive app under
<strong>Settings -> Auto Backup for apps -> Manage backup</strong>. The
backup data cannot be read by the user or other applications on the device.

<p>Backups from each device-setup-lifetime are stored in separate datasets
as shown in the following examples:
<ul>
  <li>If the user owns two devices, then a backup dataset exists for each device.
  <li>If the user factory resets a device and then sets up the device with the
    same account, the backup is stored in a new dataset. Obsolete datasets are
    automatically deleted after a period of inactivity.</li></ul>

<p class="caution"><strong>Caution:</strong> Once the amount of data reaches
25MB, the app is banned from sending data to the
cloud, even if the amount of data later falls under the 25MB threshold. The ban
affects only the offending device (not other devices that the user owns) and
lasts for the entire device-setup-lifetime. For example, if the user removes and
reinstalls the application, the ban is still in effect. The ban is lifted when
the user performs factory reset on the device.

<h2 id="BackupSchedule">Backup schedule</h2>
<p>Backups occur automatically when all of the following conditions are met:
<ul>
  <li>The user has enabled backup on the device in <strong>Settings</strong> >
    <strong>Backup &amp; Reset</strong>.
  <li>At least 24 hours have elapsed since the last backup.
  <li>The device is idle and charging.
  <li>The device is connected to a Wi-Fi network. If the device is never connected
    to a wifi network, then Auto Backup never occurs.</li></ul>

<p>In practice, these conditions occur roughly every night. To conserve network
bandwidth, upload takes place only if app data has changed.

<p>During Auto Backup, the system shuts down the app to make sure it is no longer
writing to the file system. By default, the backup system ignores apps that are
running in the foreground because users would notice their apps being shut down.
You can override the default behavior by setting the
<a href="{@docRoot}reference/android/R.attr.html#backupInForeground">backupInForeground</a>
attribute to true.

<p>To simplify testing, Android includes tools that let you manually initiate
a backup of your app. For more information, see
<a href="{@docRoot}guide/topics/data/testingbackup.html">Testing Backup and Restore</a>.

<h2 id="RestoreSchedule">Restore schedule</h2>
<p>Data is restored whenever the app is installed, either from the Play store,
during device setup (when the system installs previously installed apps), or
from running adb install. The restore operation occurs after the APK is
installed, but before the app is available to be launched by the user.

<p>During the initial device setup wizard, the user is shown a list of available backup
datasets and is asked which one to restore the data from. Whichever backup
dataset is selected becomes the ancestral dataset for the device. The device can
restore from either its own backups or the ancestral dataset. The device
prioritize its own backup if backups from both sources are available. If the
user didn't go through the device setup wizard, then the device can restore only from
its own backups.

<p>To simplify testing, Android includes tools that let you manually initiate
a restore of your app. For more information, see
<a href="{@docRoot}guide/topics/data/testingbackup.html">Testing Backup and Restore</a>.

<h2 id="EnablingAutoBackup">Enabling and disabling backup</h2>
<p>Apps that target Android 6.0 (API level 23) or higher automatically participate
in Auto Backup. This is because the
<a href="{@docRoot}reference/android/R.attr.html#allowBackup">android:allowBackup</a>
attribute, which enables/disables backup, defaults to <code>true</code> if omitted.
To avoid confusion, we recommend you explicitly set the attribute in the <code>&lt;application></code>
element of your <code>AndroidManifest.xml</code>. For example:

<pre class="prettyprint">&lt;application ...
    android:allowBackup="true">
&lt;/app></pre>

<p>To disable Auto Backup, add either of the following attributes to the
application element in your manifest file:

<ul>
  <li>set <code>android:allowBackup</code> to <code>false</code>. This completely disables data
    backup. You may want to disable backups when your app can recreate its state
    through some other mechanism or when your app deals with sensitive
    information that should not be backed up.</li>
  <li>set <code>android:allowBackup</code> to <code>true</code> and
    <code>android:fullBackupOnly</code> to <code>false</code>. With these settings,
    your app always participates in Key/Value Backup, even when running on devices that
    support Auto Backup.</li></ul>

<h2 id="IncludingFiles">Including and excluding files</h2>
<p>By default, the system backs up almost all app data. For more information,
see <a href="#Files">Files that are backed up</a>. This section shows you how to
define custom XML rules to control what gets backed up.

<ol>
  <li>In <code>AndroidManifest.xml</code>, add the <a href="{@docRoot}reference/android/R.attr.html#fullBackupContent">android:fullBackupContent</a> attribute to the
  <code>&lt;application></code> element. This attribute points to an XML file that contains backup
  rules. For example:
  <pre class="prettyprint">&lt;application ...
    android:fullBackupContent="@xml/my_backup_rules">
  &lt;/app></pre></li>
  <li>Create an XML file called <code>my_backup_rules.xml</code> in the <code>res/xml/</code> directory. Inside the file, add rules with the <code>&lt;include></code> and <code>&lt;exclude></code> elements. The following sample backs up all shared preferences except <code>device.xml</code>:
  <pre>&lt;?xml version="1.0" encoding="utf-8"?>
&lt;full-backup-content>
    &lt;include domain="sharedpref" path="."/>
    &lt;exclude domain="sharedpref" path="device.xml"/>
&lt;/full-backup-content></pre></li>

<h3 id="XMLSyntax">XML Config Syntax</h3>
<p>The XML syntax for the configuration file is shown below:

<pre class="prettyprint">&lt;full-backup-content>
    &lt;include domain=["file" | "database" | "sharedpref" | "external" | "root"]
    path="string" />
    &lt;exclude domain=["file" | "database" | "sharedpref" | "external" | "root"]
    path="string" />
&lt;/full-backup-content></pre>

<p>Inside the <code>&lt;full-backup-content></code> tag, you can define <code>&lt;include></code> and <code>&lt;exclude></code>
elements:

<ul>
  <li><code>&lt;include></code> - Specifies a file or folder to backup. By default, Auto Backup
includes almost all app files. If you specify an &lt;include> element, the system
no longer includes any files by default and backs up <em>only the files
specified</em>. To include multiple files, use multiple &lt;include> elements.
  <p>note: Files in directories returned by <code>getCacheDir()</code>, <code>getCodeCacheDir()</code>, or
<code>getNoBackupFilesDir()</code> are always excluded even if you try to include them.</li>

  <li><code>&lt;exclude></code> - Specifies a file or folder to exclude during backup. Here are
some files that are typically excluded from backup: <ul>
    <li>Files that have device specific identifiers, either issued by a server or
generated on the device. For example, <a href="https://developers.google.com/cloud-messaging/android/start">Google Cloud Messaging (GCM)</a> needs to
generate a registration token every time a user installs your app on a new
device. If the old registration token is restored, the app may behave
unexpectedly.
    <li>Account credentials or other sensitive information. Consider asking the
user to reauthenticate the first time they launch a restored app rather than
allowing for storage of such information in the backup.
    <li>Files related to app debugging, such as <a href="{@docRoot}studio/run/index.html#instant-run">instant run files</a>. To exclude instant run files, add the rule <code>&lt;exclude
domain="file" path="instant-run"/></code>
    <li>Large files that cause the app to exceed the 25MB backup quota.</li> </ul>
  </li> </ul>

<p class="note"><strong>Note:</strong> If your configuration file specifies both elements, then the
backup contains everything captured by the <code>&lt;include></code> elements minus the
resources named in the <code>&lt;exclude></code> elements. In other words,
<code>&lt;exclude></code> takes precedence.

<p>Each element must include the following two attributes:
<ul>
  <li><code>domain</code> - specifies the location of resource. Valid values for this attribute
include the following: <ul>
    <li><code>root</code> - the directory on the filesystem where all private files belonging to
this app are stored.
    <li><code>file</code> - directories returned by {@link android.content.Context#getFilesDir()}.
    <li><code>database</code> - directories returned by {@link android.content.Context#getDatabasePath(String) getDatabasePath()}.
Databases created with {@link android.database.sqlite.SQLiteOpenHelper}
are stored here.
    <li><code>sharedpref</code> - the directory where {@link android.content.SharedPreferences}
are stored.
    <li><code>external</code> the directory returned by {@link android.content.Context#getExternalFilesDir(String) getExternalFilesDir()}
    <p>Note: You cannot backup files outside of these locations.</li></ul>
  <li><code>path</code>: Specifies a file or folder to include in or exclude from backup. Note
that: <ul>
    <li>This attribute does not support wildcard or regex syntax.
    <li>You can use <code>.</code> to reference the current directory, however, you cannot
reference the parent directory <code>..</code> for security reasons.
    <li>If you specify a directory, then the rule applies to all files in the
directory and recursive sub-directories.</li></ul></li></ul>

<h2 id="ImplementingBackupAgent">Implementing BackupAgent</h2>
<p>Apps that implement Auto Backup do not need to implement {@link android.app.backup.BackupAgent}. However, you can optionally implement a custom {@link android.app.backup.BackupAgent}. Typically, there are two reasons for doing this:
<ul>
  <li>You want to receive notification of backup events such as,
{@link android.app.backup.BackupAgent#onRestoreFinished()} or {@link android.app.backup.BackupAgent#onQuotaExceeded(long,long)}. These callback methods are executed
even if the app is not running.
<li>You can't easily express the set of files you want to backup with XML rules.
In these very rare cases, you can implement a BackupAgent that overrides {@link android.app.backup.BackupAgent#onFullBackup(FullBackupDataOutput)} to
store what you want. To retain the system's default implementation, call the
corresponding method on the superclass with <code>super.onFullBackup()</code>.</li></ul>

<p class="note"><strong>Note:</strong> Your <code>BackupAgent</code> must
implement the abstract methods
{@link android.app.backup.BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor) onBackup()}
and {@link android.app.backup.BackupAgent#onRestore(BackupDataInput,int,ParcelFileDescriptor) onRestore()}.
Those methods are used for Key/Value Backup. So if
you are not using Key/Value Backup, implement those methods and leave them blank.

<p>For more information, see
<a href="{@docRoot}guide/topics/data/keyvaluebackup.html#BackupAgent">Extending
BackupAgent</a>.