BackupDataOutput

public class BackupDataOutput
extends Object

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);
     ...
 }

Summary

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 millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.

Public methods

int writeEntityData (byte[] data, 
                int size)

int writeEntityHeader (String key, 
                int dataSize)