private SettableDraweeHierarchy getSettableDraweeHierarchy() {
    SettableDraweeHierarchy hierarchy = mSettableDraweeHierarchy;
    if (hierarchy == null) {
      throw new IllegalStateException(
          "mSettableDraweeHierarchy is null; Caller context: " + mCallerContext);
    }
    return hierarchy;
  }
Returns whether the gesture should be handled by the controller
drawee/src/main/java/com/facebook/drawee/controller/AbstractDraweeController.java