AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.backupagentsample"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:backupAgent="com.example.backupagentsample.MyBackupAgent"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <meta-data android:name="com.google.android.backup.api_key"
               android:value="AEdPqrEAAAAIg-APWubuFTxLp5DLMzGQnBNifZdlOJcB9TxK7A" />
        <activity
            android:name="com.example.backupagentsample.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

MainActivity.java

package com.example.backupagentsample;

import android.os.Bundle;
import android.app.Activity;
import android.app.backup.BackupManager;
import android.view.Menu;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        new BackupManager(this).dataChanged();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

MyBackupAgent.java

package com.example.backupagentsample;

import android.app.backup.BackupAgent;
import android.app.backup.BackupDataInput;
import android.app.backup.BackupDataOutput;
import android.os.ParcelFileDescriptor;
import android.util.Log;

import java.io.IOException;

public class MyBackupAgent extends BackupAgent {

    @Override
    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
            ParcelFileDescriptor newState) throws IOException {
        Log.d("hoge", "begin backup");
        data.writeEntityHeader("hoge", 10);
        data.writeEntityData(new byte[] {0,1,2,3,4,5,6,7,8,9}, 10);
        Log.d("hoge", "end backup");
    }

    @Override
    public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)
            throws IOException {
        Log.d("hoge", "begin restore");
        if (data.readNextHeader()) {
            final String key = data.getKey();
            final int size = data.getDataSize();
            final byte[] buffer = new byte[size];
            data.readEntityData(buffer, 0, size);
            
            Log.d("hoge", "buffer[3]: " + buffer[3]);
        }
    }

}