BackupDataOutput

Class Overview

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

[Expand] Inherited Methods

From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Invoked when the garbage collector has detected that this instance is no longer reachable. final Class<?> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.