How can I use the class ViewControlLayer to change the Camera view or Map view?（Android Core）

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The class ViewControlLayer http://docs.ros.org/indigo/api/androi...

Here is the Construction method:

public ViewControlLayer(final Context context,
                        final ExecutorService executorService,
                        final RosImageView<CompressedImage> cameraView,
                        final VisualizationView mapView,
                        final ViewGroup mainLayout,
                        final ViewGroup sideLayout,
                        final AppParameters params) {

    this.context = context;

    listeners = new ListenerGroup<CameraControlListener>(executorService);

    this.cameraView = cameraView;
    this.mapView = mapView;
    this.mainLayout = mainLayout;
    this.sideLayout = sideLayout;

    viewMode = ViewMode.CAMERA;
    this.cameraView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v){
            swapViews();
        }
    });

    this.mapView.setClickable(true);
    this.cameraView.setClickable(false);
    this.robotFrame = (String) params.get("robot_frame", context.getString(R.string.robot_frame));
    mapViewGestureAvaiable = false;
}

This is my code(Method in onCreate()):

visualizationView.onCreate(Lists.<Layer>newArrayList(new CameraControlLayer(),
            new OccupancyGridLayer("map"), new PathLayer("move_base/NavfnROS/plan"), new PathLayer(
                    "move_base_dynamic/NavfnROS/plan"), new LaserScanLayer("base_scan"),
            new PoseSubscriberLayer("simple_waypoints_server/goal_pose"), new PosePublisherLayer(
                    "simple_waypoints_server/goal_pose"), new RobotLayer("base_footprint")));

I want to use the ViewControlLayer like this to change the Canera view or Map view,how can i do it?

(Method in init(NodeMainExecutor nodeMainExecutor))

visualizationView.onCreate(Lists.<Layer>newArrayList(new ViewControlLayer(this,
            nodeMainExecutor.getScheduledExecutorService(), cameraView,
            mapView, mainLayout, sideLayout, params),
            new OccupancyGridLayer("map"), new PathLayer("move_base/NavfnROS/plan"), new PathLayer(
                    "move_base_dynamic/NavfnROS/plan"), new LaserScanLayer("base_scan"),
            new PoseSubscriberLayer("simple_waypoints_server/goal_pose"), new PosePublisherLayer(
                    "simple_waypoints_server/goal_pose"), new RobotLayer("base_footprint")));

The error maybe occur at the ViewControlLayer Construction method：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.concurrent.ScheduledExecutorService org.ros.android.NodeMainExecutorService.getScheduledExecutorService()' on a null object reference at com.robot.et.myteleop.MainActivity.onCreate(MainActivity.java:65) at android.app.Activity.performCreate(Activity.java:6374) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2752) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2873)  at android.app.ActivityThread.access$900(ActivityThread.java:181)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1482)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:145)  at android.app.ActivityThread.main(ActivityThread.java:6145)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)