@Override
  public boolean getPadding(Rect padding) {
    padding.left = 0;
    padding.top = 0;
    padding.right = 0;
    padding.bottom = 0;
    final Rect rect = mTmpRect;
    for (int i = 0; i < mLayers.length; i++) {
      Drawable drawable = mLayers[i];
      if (drawable != null) {
        drawable.getPadding(rect);
        padding.left = Math.max(padding.left, rect.left);
        padding.top = Math.max(padding.top, rect.top);
        padding.right = Math.max(padding.right, rect.right);
        padding.bottom = Math.max(padding.bottom, rect.bottom);
      }
    }
    return true;
  }
Sets a new drawable at the specified index, and return the previous drawable, if any.
drawee/src/main/java/com/facebook/drawee/drawable/ArrayDrawable.java