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BackupDataInput

public class BackupDataInput
extends Object

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


Provides the structured interface through which a BackupAgent reads information from the backup data set, via its onRestore() method. The data is presented as a set of "entities," each representing one named record as previously stored by the agent's onBackup() implementation. An entity is composed of a descriptive header plus a byte array that holds the raw data saved in the remote backup.

The agent must consume every entity in the data stream, otherwise the restored state of the application will be incomplete.

Example

A typical onRestore() implementation might be structured something like this:

 public void onRestore(BackupDataInput data, int appVersionCode,
                       ParcelFileDescriptor newState) {
     while (data.readNextHeader()) {
         String key = data.getKey();
         int dataSize = data.getDataSize();

         if (key.equals(MY_BACKUP_KEY_ONE)) {
             // process this kind of record here
             byte[] buffer = new byte[dataSize];
             data.readEntityData(buffer, 0, dataSize); // reads the entire entity at once

             // now 'buffer' holds the raw data and can be processed however
             // the agent wishes
             processBackupKeyOne(buffer);
         } else if (key.equals(MY_BACKUP_KEY_TO_IGNORE) {
             // a key we recognize but wish to discard
             data.skipEntityData();
         } // ... etc.
    }
 }

Summary

Public methods

int getDataSize()

Report the size in bytes of the data associated with the current entity in the restore stream.

String getKey()

Report the key associated with the current entity in the restore stream

int readEntityData(byte[] data, int offset, int size)

Read a record's raw data from the restore stream.

boolean readNextHeader()

Extract the next entity header from the restore stream.

void skipEntityData()

Consume the current entity's data without extracting it into a buffer for further processing.

Inherited methods

From class java.lang.Object

Public methods

getDataSize

Added in API level 8
int getDataSize ()

Report the size in bytes of the data associated with the current entity in the restore stream.

Returns
int The size of the record's raw data, in bytes
Throws
IllegalStateException if the next record header has not yet been read

getKey

Added in API level 8
String getKey ()

Report the key associated with the current entity in the restore stream

Returns
String the current entity's key string
Throws
IllegalStateException if the next record header has not yet been read

readEntityData

Added in API level 8
int readEntityData (byte[] data, 
                int offset, 
                int size)

Read a record's raw data from the restore stream. The record's header must first have been processed by the readNextHeader() method. Multiple calls to this method may be made in order to process the data in chunks; not all of it must be read in a single call. Once all of the raw data for the current entity has been read, further calls to this method will simply return zero.

Parameters
data byte: An allocated byte array of at least 'size' bytes
offset int: Offset within the 'data' array at which the data will be placed when read from the stream
size int: The number of bytes to read in this pass
Returns
int The number of bytes of data read. Once all of the data for this entity has been read, further calls to this method will return zero.
Throws
IOException if an error occurred when trying to read the restore data stream

readNextHeader

Added in API level 8
boolean readNextHeader ()

Extract the next entity header from the restore stream. After this method return success, the getKey() and getDataSize() methods can be used to inspect the entity that is now available for processing.

Returns
boolean true when there is an entity ready for consumption from the restore stream, false if the restore stream has been fully consumed.
Throws
IOException if an error occurred while reading the restore stream

skipEntityData

Added in API level 8
void skipEntityData ()

Consume the current entity's data without extracting it into a buffer for further processing. This allows a BackupAgent to efficiently discard obsolete or otherwise uninteresting records during the restore operation.

Throws
IOException if an error occurred when trying to read the restore data stream
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