BackupDataOutput

Kotlin |Java

public class BackupDataOutput
extends Object

java.lang.Object
↳	android.app.backup.BackupDataOutput

Provides the structured interface through which a BackupAgent commits information to the backup data set, via its onBackup() method. Data written for backup is presented as a set of "entities," key/value pairs in which each binary data record "value" is named with a string "key."

To commit a data record to the backup transport, the agent's onBackup() method first writes an "entity header" that supplies the key string for the record and the total size of the binary value for the record. After the header has been written, the agent then writes the binary entity value itself. The entity value can be written in multiple chunks if desired, as long as the total count of bytes written matches what was supplied to writeEntityHeader().

Entity key strings are considered to be unique within a given application's backup data set. If a backup agent writes a new entity under an existing key string, its value will replace any previous value in the transport's remote data store. You can remove a record entirely from the remote data set by writing a new entity header using the existing record's key, but supplying a negative dataSize parameter. When you do so, the agent does not need to call writeEntityData(byte[], int).

Example

Here is an example illustrating a way to back up the value of a String variable called mStringToBackUp:

 static final String MY_STRING_KEY = "storedstring";

 public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
         throws IOException {
     ...
     byte[] stringBytes = mStringToBackUp.getBytes();
     data.writeEntityHeader(MY_STRING_KEY, stringBytes.length);
     data.writeEntityData(stringBytes, stringBytes.length);
     ...
 }

See also:

BackupAgent

Summary

Public methods
`long`	`getQuota()` Returns the quota in bytes for the application's current backup operation.
`int`	`getTransportFlags()` Returns flags with additional information about the backup transport.
`int`	`writeEntityData(byte[] data, int size)` Write a chunk of data under the current entity to the backup transport.
`int`	`writeEntityHeader(String key, int dataSize)` Mark the beginning of one record in the backup data stream.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

getQuota

Added in API level 26

public long getQuota ()

Returns the quota in bytes for the application's current backup operation. The value can vary for each operation.

Returns
`long`

See also:

FullBackupDataOutput.getQuota()

getTransportFlags

Added in API level 28

public int getTransportFlags ()

Returns flags with additional information about the backup transport. For supported flags see BackupAgent

Returns
`int`

See also:

FullBackupDataOutput.getTransportFlags()

writeEntityData

Added in API level 8

public int writeEntityData (byte[] data, 
                int size)

Write a chunk of data under the current entity to the backup transport.

Parameters
`data`	`byte`: A raw data buffer to send
`size`	`int`: The number of bytes to be sent in this chunk

Returns
`int`	the number of bytes written

Throws
`IOException`	if the write failed

writeEntityHeader

Added in API level 8

public int writeEntityHeader (String key, 
                int dataSize)

Mark the beginning of one record in the backup data stream. This must be called before writeEntityData(byte, int).

Parameters
`key`	`String`: A string key that uniquely identifies the data record within the application. Keys whose first character is \uff00 or higher are not valid.
`dataSize`	`int`: The size in bytes of this record's data. Passing a dataSize of -1 indicates that the record under this key should be deleted.

Returns
`int`	The number of bytes written to the backup stream

Throws
`IOException`	if the write failed