Files that are backed up
By default, Auto Backup includes files in most of the directories that are assigned to your app by the system:
- Shared preferences files.
- Files in the directory returned by
- Files in the directory returned by
getDatabasePath(String), which also includes files created with the
- Files in directories created with
- Files on external storage in the directory returned by
Auto Backup excludes files in directories returned by
getNoBackupFilesDir(). The files saved
in these locations are only needed temporarily, or are intentionally
excluded from backup operations.
You can configure your app to include and exclude particular files. For more information, see the Include and exclude files section.
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.
Users can see a list of apps that have been backed up in the Google Drive app under Settings -> Auto Backup for apps -> Manage backup. The backup data cannot be read by the user or other applications on the device.
Backups from each device-setup-lifetime are stored in separate datasets as shown in the following examples:
- If the user owns two devices, then a backup dataset exists for each device.
- 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.
Caution: If the amount of data is over
25MB, the system fires the
callback and does not backup data to the cloud. The system periodically checks
whether the amount of data later falls under the 25MB threshold and continues
Auto Backup when it does.
Backups occur automatically when all of the following conditions are met:
- The user has enabled backup on the device in Settings > Backup & Reset.
- At least 24 hours have elapsed since the last backup.
- The device is idle and charging.
- The device is connected to a Wi-Fi network. If the device is never connected to a wifi network, then Auto Backup never occurs.
In practice, these conditions occur roughly every night. To conserve network bandwidth, upload takes place only if app data has changed.
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
attribute to true.
To simplify testing, Android includes tools that let you manually initiate a backup of your app. For more information, see Testing Backup and Restore.
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.
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.
To simplify testing, Android includes tools that let you manually initiate a restore of your app. For more information, see Testing Backup and Restore.
Enabling and disabling backup
Apps that target Android 6.0 (API level 23) or higher automatically participate
in Auto Backup. This is because the
attribute, which enables/disables backup, defaults to
true if omitted.
To avoid confusion, we recommend you explicitly set the attribute in the
element of your
AndroidManifest.xml. For example:
<application ... android:allowBackup="true"> </app>
To disable Auto Backup, set
false. 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.
Including and excluding files
By default, the system backs up almost all app data. For more information, see Files that are backed up. This section shows you how to define custom XML rules to control what gets backed up.
AndroidManifest.xml, add the
android:fullBackupContentattribute to the
<application>element. This attribute points to an XML file that contains backup rules. For example:
<application ... android:fullBackupContent="@xml/my_backup_rules"> </app>
- Create an XML file called
res/xml/directory. Inside the file, add rules with the
<exclude>elements. The following sample backs up all shared preferences except
<?xml version="1.0" encoding="utf-8"?> <full-backup-content> <include domain="sharedpref" path="."/> <exclude domain="sharedpref" path="device.xml"/> </full-backup-content>
XML Config Syntax
The XML syntax for the configuration file is shown below:
<full-backup-content> <include domain=["file" | "database" | "sharedpref" | "external" | "root"] path="string" /> <exclude domain=["file" | "database" | "sharedpref" | "external" | "root"] path="string" /> </full-backup-content>
<full-backup-content> tag, you can define
<include>- Specifies a file or folder to backup. By default, Auto Backup includes almost all app files. If you specify an <include> element, the system no longer includes any files by default and backs up only the files specified. To include multiple files, use multiple <include> elements.
note: Files in directories returned by
getNoBackupFilesDir()are always excluded even if you try to include them.
<exclude>- Specifies a file or folder to exclude during backup. Here are some files that are typically excluded from backup:
- Files that have device specific identifiers, either issued by a server or generated on the device. For example, Google Cloud Messaging (GCM) 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.
- 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.
- Files related to app debugging, such as instant run files. To exclude instant run files, add the rule
<exclude domain="file" path="instant-run"/>
- Large files that cause the app to exceed the 25MB backup quota.
Note: If your configuration file specifies both elements, then the
backup contains everything captured by the
<include> elements minus the
resources named in the
<exclude> elements. In other words,
<exclude> takes precedence.
Each element must include the following two attributes:
domain- specifies the location of resource. Valid values for this attribute include the following:
root- the directory on the filesystem where all private files belonging to this app are stored.
file- directories returned by
database- directories returned by
getDatabasePath(). Databases created with
SQLiteOpenHelperare stored here.
sharedpref- the directory where
externalthe directory returned by
Note: You cannot backup files outside of these locations.
path: Specifies a file or folder to include in or exclude from backup. Note that:
- This attribute does not support wildcard or regex syntax.
- You can use
.to reference the current directory, however, you cannot reference the parent directory
..for security reasons.
- If you specify a directory, then the rule applies to all files in the directory and recursive sub-directories.
- You want to receive notification of backup events such as,
onQuotaExceeded(long, long). These callback methods are executed even if the app is not running.
- You can't easily express the set of files you want to backup with XML rules. In these
rare cases, you can implement a BackupAgent that overrides
onFullBackup(FullBackupDataOutput)to store what you want. To retain the system's default implementation, call the corresponding method on the superclass with
If you implement a BackupAgent, by default the system expects your app to
perform key/value backup and restore. To use the file-based Auto Backup
instead, set the
true in your app's manifest.
During auto backup and restore operations, the system launches the app in a
restricted mode to both prevent the app from accessing files that could cause
conflicts and let the app execute callback methods in its
BackupAgent. In this restricted mode, the app's main
activity is not automatically launched, its Content Providers
are not initialized, and the base-class
instantiated instead of any subclass declared in the app's manifest. To
avoid errors, make sure that the parts of your app that execute in the
restricted mode (mostly your
BackupAgent) do not
access content providers in the same app or attempt to cast the
Application object. If you cannot avoid those patterns, then
consider implementing Key/Value backup or
disabling backup entirely.
implement the abstract methods
Those methods are used for Key/Value Backup. So if
you are not using Key/Value Backup, implement those methods and leave them blank.
For more information, see Extending BackupAgent.