public @Nullable Drawable setCurrent(@Nullable Drawable newDelegate) {
    Drawable previousDelegate = setCurrentWithoutInvalidate(newDelegate);
    invalidateSelf();
    return previousDelegate;
  }
Sets a new drawable to be the delegate, and returns the old one (or null).

<p>This method will cause the drawable to be invalidated.

@param newDelegate
@return the previous delegate
drawee/src/main/java/com/facebook/drawee/drawable/ForwardingDrawable.java