如何直接应用移动wallpper

Question

我制作了移动壁纸的代码，但是按下按钮时，壁纸会添加到手机壁纸中，但它不会作为活动壁纸应用，我必须手动添加它 我的服务代码是

public class LiveWallpaperService extends WallpaperService {
int x, y;

public void onCreate() {
    super.onCreate();
}

public void onDestroy() {
    super.onDestroy();
}

public Engine onCreateEngine() {
    return new MyWallpaperEngine();
}

class MyWallpaperEngine extends Engine {

    private final Handler handler = new Handler();
    private final Runnable drawRunner = new Runnable() {
        @Override
        public void run() {
            draw();
        }
    };
    private boolean visible = true;
    public Bitmap image1, backgroundImage;

    MyWallpaperEngine() {
        // get the fish and background image references
        image1 = BitmapFactory.decodeResource(getResources(), R.drawable.fish);

        backgroundImage = BitmapFactory.decodeResource(getResources(), R.drawable.background);
        x = 200; // initialize x position
        y = -200;  // initialize y position

    }


    public void onCreate(SurfaceHolder surfaceHolder) {
        super.onCreate(surfaceHolder);
    }

    @Override
    public void onVisibilityChanged(boolean visible) {
        this.visible = visible;
        // if screen wallpaper is visible then draw the image otherwise do not draw
        if (visible) {
            handler.post(drawRunner);
        } else {
            handler.removeCallbacks(drawRunner);
        }
    }

    @Override
    public void onSurfaceDestroyed(SurfaceHolder holder) {
        super.onSurfaceDestroyed(holder);
        this.visible = false;
        handler.removeCallbacks(drawRunner);
    }

    public void onOffsetsChanged(float xOffset, float yOffset, float xStep, float yStep, int xPixels, int yPixels) {
        draw();
    }

    void draw() {
        final SurfaceHolder holder = getSurfaceHolder();

        Canvas c = null;
        try {
            c = holder.lockCanvas();
            // clear the canvas
            c.drawColor(Color.BLACK);
            if (c != null) {
                // draw the background image
                c.drawBitmap(backgroundImage, 0, 0, null);
                // draw the fish
                c.drawBitmap(image1, x, y, null);


                // get the width of canvas
                int height = c.getHeight();
                int width = c.getWidth();

                // if x crosses the width means  x has reached to right edge
                if (y > height + 100) {
                    // assign initial value to start with
                    y = 200;
                }
                // change the x position/value by 1 pixel
                y = y + 1;
                if (x > width + 100) {
                    x = -50;
                    x = x + 3;
                }

            }
        } finally {
            if (c != null)
                holder.unlockCanvasAndPost(c);
        }

        handler.removeCallbacks(drawRunner);
        if (visible) {
            handler.postDelayed(drawRunner, 10); // delay 10 mileseconds
        }


    }
}
}   

以及启动该服务的主要活动代码是

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

public void startClicked(View view) {
    Intent intent = new Intent(this, LiveWallpaperService.class);
    startService(intent);
}