code: public void onResume(boolean retainedInstance) {
          if (mBlurredBackgroundView == null || retainedInstance) {
              if (mHoldingActivity.getWindow().getDecorView().isShown()) {
                  mBluringTask = new BlurAsyncTask();
                  mBluringTask.execute();
              } else {
                  mHoldingActivity.getWindow().getDecorView().getViewTreeObserver().addOnPreDrawListener(
                      new ViewTreeObserver.OnPreDrawListener() {
                          @Override
                          public boolean onPreDraw() {
                              // dialog can have been closed before being drawn
                              if (mHoldingActivity != null) {
                                  mHoldingActivity.getWindow().getDecorView()
                                      .getViewTreeObserver().removeOnPreDrawListener(this);
                                  mBluringTask = new BlurAsyncTask();
                                  mBluringTask.execute();
                              }
                              return true;
                          }
                      }
                  );
              }
          }
      }
docs: Resume the engine.
  
  @param retainedInstance use getRetainInstance.