android/app/backup/BackupAgentHelper.java

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.app.backup;

import android.os.ParcelFileDescriptor;

import java.io.IOException;

/**
 * A convenient {@link BackupAgent} wrapper class that automatically manages
 * heterogeneous data sets within the backup data, each identified by a unique
 * key prefix.  When processing a backup or restore operation, the BackupAgentHelper
 * dispatches to one or more installed {@link BackupHelper} objects, each
 * of which is responsible for a defined subset of the data being processed.
 * <p>
 * An application will typically extend this class in its own
 * backup agent. Then, within the agent's {@link BackupAgent#onCreate() onCreate()}
 * method, it will call {@link #addHelper(String, BackupHelper) addHelper()} one or more times to
 * install the handlers for each kind of data it wishes to manage within its backups.
 * <p>
 * The Android framework currently provides two predefined {@link BackupHelper} classes:</p>
 * <ul><li>{@link FileBackupHelper} - Manages the backup and restore of entire files
 * within an application's data directory hierarchy.</li>
 * <li>{@link SharedPreferencesBackupHelper} - Manages the backup and restore of an
 * application's {@link android.content.SharedPreferences} data.</li></ul>
 * <p>
 * An application can also implement its own helper classes to work within the
 * {@link BackupAgentHelper} framework.  See the {@link BackupHelper} interface
 * documentation for details.
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about using BackupAgentHelper, read the
 * <a href="{@docRoot}guide/topics/data/backup.html">Data Backup</a> developer guide.</p>
 * </div>
 *
 * @see BackupHelper
 * @see FileBackupHelper
 * @see SharedPreferencesBackupHelper
 */
public class BackupAgentHelper extends BackupAgent {
    static final String TAG = "BackupAgentHelper";

    BackupHelperDispatcher mDispatcher = new BackupHelperDispatcher();

    /**
     * Run the backup process on each of the configured handlers.
     */
    @Override
    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
             ParcelFileDescriptor newState) throws IOException {
        mDispatcher.performBackup(oldState, data, newState);
    }

    /**
     * Run the restore process on each of the configured handlers.
     */
    @Override
    public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)
            throws IOException {
        mDispatcher.performRestore(data, appVersionCode, newState);
    }

    /** @hide */
    public BackupHelperDispatcher getDispatcher() {
        return mDispatcher;
    }

    /**
     * Add a helper for a given data subset to the agent's configuration.  Each helper
     * must have a prefix string that is unique within this backup agent's set of
     * helpers.
     *
     * @param keyPrefix A string used to disambiguate the various helpers within this agent
     * @param helper A backup/restore helper object to be invoked during backup and restore
     *    operations.
     */
    public void addHelper(String keyPrefix, BackupHelper helper) {
        mDispatcher.addHelper(keyPrefix, helper);
    }
}