<service android:name=".ChangeService"></service>

public class ChangeService extends Service {  int[] wallpapers = new int[]{      R.drawable.a2, R.drawable.a3, R.drawable.a4  };  WallpaperManager wallpaperManager;  int current = 0;  @Override  public void onCreate() {    super.onCreate();    wallpaperManager = WallpaperManager.getInstance(this);  }  @Override  public int onStartCommand(Intent intent, int flags, int startId) {    if (current >= 3) {      current = 0;    } try {      wallpaperManager.setResource(wallpapers[current++]);    } catch (IOException e) {      e.printStackTrace();    } return START_STICKY;  }  @Nullable  @Override  public IBinder onBind(Intent intent) {    return null;  }}

public class MainActivity extends Activity {  private Button mStart;  private Button mStop;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    mStart = (Button) findViewById(R.id.start);    mStop = (Button) findViewById(R.id.stop);    final Intent intent = new Intent(MainActivity.this, ChangeService.class);     final PendingIntent pi = PendingIntent.getService(MainActivity.this, 0, intent, 0);     mStart.setOnClickListener(new View.OnClickListener() {       @Override       public void onClick(View v) {         AlarmManager alarmManager = (AlarmManager) getSystemService(Service.ALARM_SERVICE);         alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, 0, 2000, pi);         mStart.setEnabled(false); mStop.setEnabled(true);         Toast.makeText(MainActivity.this, "壁紙定時更換啟動成功啦", Toast.LENGTH_SHORT).show();       }     });     mStop.setOnClickListener(new View.OnClickListener() {       @Override public void onClick(View v) {         mStart.setEnabled(true);       mStop.setEnabled(false);       AlarmManager alarmManager = (AlarmManager) getSystemService(Service.ALARM_SERVICE);        alarmManager.cancel(pi);       }     });  }}

<?xml version="1.0" encoding="utf-8"?><RelativeLayout  xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical" >  <LinearLayout    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:layout_alignParentBottom="true"    android:orientation="horizontal">    <Button      android:id="@+id/start"      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:layout_weight="1"      android:gravity="center_horizontal"      android:text="Start"      android:textSize="25dp"      android:textColor="#ffffffff"/>    <Button      android:id="@+id/stop"      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:layout_weight="1"      android:gravity="center_horizontal"      android:text="Stop"      android:textSize="25dp"      android:textColor="#ffffffff"/>  </LinearLayout></RelativeLayout>