code: @Override
      public void setAlpha(int alpha) {
          if (mAlpha != alpha) {
              mAlpha = alpha;
              if (mCurrDrawable != null) {
                  if (mEnterAnimationEnd == 0) {
                      mCurrDrawable.setAlpha(alpha);
                  } else {
                      animate(false);
                  }
              }
          }
      }
docs: TODO
  
  @Override public Insets getLayoutInsets() { return (mCurrDrawable ==
  null) ? Insets.NONE : mCurrDrawable.getLayoutInsets(); }