public DrawableParent getDrawableParentForIndex(int index) {
    Preconditions.checkArgument(index >= 0);
    Preconditions.checkArgument(index < mDrawableParents.length);
    if (mDrawableParents[index] == null) {
      mDrawableParents[index] = createDrawableParentForIndex(index);
    }
    return mDrawableParents[index];
  }
Gets the {@code DrawableParent} for index.
drawee/src/main/java/com/facebook/drawee/drawable/ArrayDrawable.java