如何实现让app变成灰色

    Paint mPaint = new Paint();
    ColorMatrix mColorMatrix = new ColorMatrix();
    mColorMatrix.setSaturation(0);
    mPaint.setColorFilter(new ColorMatrixColorFilter(mColorMatrix));

  public class ActivityLifecycle implements Application.ActivityLifecycleCallbacks, Closeable {
    
      public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
      View decorView = activity.getWindow().getDecorView();
      decorView.setLayerType(View.LAYER_TYPE_HARDWARE, mPaint);
}}