assigning to 'id<UIGestureRecognizerDelegate> _Nullable' from incompatible

tip:参考 http://stackoverflow.com/questions/9861538/assigning-to-iddelegate-from-incompatible-type-viewcontroller-const-strong

我的问题的解决：UIGestureRecognizerDelegate忘记添加协议

@interface：XXXX()<UIGestureRecognizerDelegate>