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)
.
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);
...
}
Public Methods | |||||||||||
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Write a chunk of data under the current entity to the backup transport.
| |||||||||||
Mark the beginning of one record in the backup data stream.
|
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Inherited Methods | |||||||||||
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From class
java.lang.Object
|
Write a chunk of data under the current entity to the backup transport.
data | A raw data buffer to send |
---|---|
size | The number of bytes to be sent in this chunk |
IOException | if the write failed |
---|
Mark the beginning of one record in the backup data stream. This must be called before
writeEntityData(byte[], int)
.
key | A string key that uniquely identifies the data record within the application. Keys whose first character is or higher are not valid. |
---|---|
dataSize | The size in bytes of this record's data. Passing a dataSize of -1 indicates that the record under this key should be deleted. |
IOException | if the write failed |
---|