BackupDataOutput

open class 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 <code><a docref="android.app.backup.BackupAgent$onBackup(android.os.ParcelFileDescriptor, android.app.backup.BackupDataOutput, android.os.ParcelFileDescriptor)">onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)</a></code>throws IOException {
      ...
      byte[] stringBytes = mStringToBackUp.getBytes();
      data.writeEntityHeader(MY_STRING_KEY, stringBytes.length);
      data.writeEntityData(stringBytes, stringBytes.length);
      ...
  }

Summary

Public methods

open fun getQuota(): Long

open fun getTransportFlags(): Int

open fun writeEntityData(
    data: ByteArray!, 
    size: Int
): Int

open fun writeEntityHeader(
    key: String!, 
    dataSize: Int
): Int