title: How to do when the activity back to the background forced to redraw the view
body: <p>Help！
  I want to re-draw the page in the app back to the background, but the addView method does not work, the system did not call the onDraw method。</p>
  
  <p>I tried calling the invalidate method and the requestLayout method, but it did not have any effect. Is there any way to solve it? Here is the main code.</p>
  
  <pre><code>private Handler handler = new Handler(Looper.getMainLooper());
  FragmentLayout view1 = (FrameLayout)getWindow().getDecorView();
  
  @Override
  protected void onPause() {
      super.onPause();
      handler.post(new Runnable() {
          @Override
          public void run() {
              addRenderScriptBitmap();
          }
      });
      getWindow().getDecorView().findViewById(android.R.id.content).invalidate();
      getWindow().getDecorView().findViewById(android.R.id.content).requestLayout();
  
  }
  
  
  private void addRenderScriptBitmap() {
      view1.setDrawingCacheEnabled(true);
      view1.buildDrawingCache();
      Bitmap bitmap = view1.getDrawingCache();
  
      ImageView imageView = new ImageView(MainActivity.this);
      imageView.setLayoutParams(new LinearLayoutCompat.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
      imageView.setImageBitmap(renderScriptBitmap(bitmap, MainActivity.this, 16.f));
      view1.addView(imageView);//This method does not work
  }
  
  public Bitmap renderScriptBitmap(Bitmap sentBitmap, Context context, float radius) {
      Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);
  
  
      final RenderScript rs = RenderScript.create(context);
      final Allocation input = Allocation.createFromBitmap(rs, sentBitmap, Allocation.MipmapControl.MIPMAP_NONE,
              Allocation.USAGE_SCRIPT);
      final Allocation output = Allocation.createTyped(rs, input.getType());
      final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
      script.setRadius(radius /* e.g. 3.f */);
      script.setInput(input);
      script.forEach(output);
      output.copyTo(bitmap);
      return bitmap;
  }
  </code></pre>
  
  <p>I want the application to fall back into the background when it becomes like this：
  <a href="https://i.stack.imgur.com/Q0CN6.png" rel="nofollow noreferrer">enter image description here</a></p>