BackupDataInput

Kotlin |Java

open class BackupDataInput

kotlin.Any
↳	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 android.app.backup.BackupAgent#onBackup(ParcelFileDescriptor,android.app.backup.BackupDataOutput,ParcelFileDescriptor) 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 android.app.backup.BackupAgent#onRestore(android.app.backup.BackupDataInput,int,ParcelFileDescriptor) 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
open Int	`getDataSize()` Report the size in bytes of the data associated with the current entity in the restore stream.
open String!	`getKey()` Report the key associated with the current entity in the restore stream
open Int	`readEntityData(data: ByteArray!, offset: Int, size: Int)` Read a record's raw data from the restore stream.
open Boolean	`readNextHeader()` Extract the next entity header from the restore stream.
open Unit	`skipEntityData()` Consume the current entity's data without extracting it into a buffer for further processing.

Public methods

getDataSize

Added in API level 8

open fun getDataSize(): Int

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

Return
`Int`	The size of the record's raw data, in bytes

Exceptions
`java.lang.IllegalStateException`	if the next record header has not yet been read

getKey

Added in API level 8

open fun getKey(): String!

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

Return
`String!`	the current entity's key string

Exceptions
`java.lang.IllegalStateException`	if the next record header has not yet been read

readEntityData

Added in API level 8

open fun readEntityData(
    data: ByteArray!, 
    offset: Int, 
    size: Int
): Int

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`	ByteArray!: 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

Return
`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.

Exceptions
`java.io.IOException`	if an error occurred when trying to read the restore data stream

readNextHeader

Added in API level 8

open fun readNextHeader(): Boolean

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.

Return
`Boolean`	`true` when there is an entity ready for consumption from the restore stream, `false` if the restore stream has been fully consumed.

Exceptions
`java.io.IOException`	if an error occurred while reading the restore stream

skipEntityData

Added in API level 8

open fun skipEntityData(): Unit

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

Exceptions
`java.io.IOException`	if an error occurred when trying to read the restore data stream