BackupDataOutput
public
class
BackupDataOutput
extends Object
java.lang.Object | |
↳ | android.app.backup.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 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);
...
}
See also:
Summary
Public methods | |
---|---|
long
|
getQuota()
Returns the quota in bytes for the application's current backup operation. |
int
|
getTransportFlags()
Returns flags with additional information about the backup transport. |
int
|
writeEntityData(byte[] data, int size)
Write a chunk of data under the current entity to the backup transport. |
int
|
writeEntityHeader(String key, int dataSize)
Mark the beginning of one record in the backup data stream. |
Inherited methods | |||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Public methods
getQuota
public long getQuota ()
Returns the quota in bytes for the application's current backup operation. The value can vary for each operation.
Returns | |
---|---|
long |
See also:
getTransportFlags
public int getTransportFlags ()
Returns flags with additional information about the backup transport. For supported flags see
BackupAgent
Returns | |
---|---|
int |
See also:
writeEntityData
public int writeEntityData (byte[] data, int size)
Write a chunk of data under the current entity to the backup transport.
Parameters | |
---|---|
data |
byte : A raw data buffer to send |
size |
int : The number of bytes to be sent in this chunk |
Returns | |
---|---|
int |
the number of bytes written |
Throws | |
---|---|
IOException |
if the write failed |
writeEntityHeader
public int writeEntityHeader (String key, int dataSize)
Mark the beginning of one record in the backup data stream. This must be called before
writeEntityData(byte, int)
.
Parameters | |
---|---|
key |
String : A string key that uniquely identifies the data record within the application.
Keys whose first character is \uff00 or higher are not valid. |
dataSize |
int : The size in bytes of this record's data. Passing a dataSize
of -1 indicates that the record under this key should be deleted. |
Returns | |
---|---|
int |
The number of bytes written to the backup stream |
Throws | |
---|---|
IOException |
if the write failed |