1
- [person test]:unrecognized selector sent to instance.
给penson对象发送一个不能识别的消息：test
2
set/get方法死循环错误：
- (void)setAge:(int)age{ self.age = age; }
-(void)age{return self.age;}
3
storyboard连线出错
setValue:forUnderfinedkey:I:this class is not key value coding-compliant for the key sumlabel.
4
错误：某个对象没有实现某个方法
- [MJViewController up] ： unrecognized selector sent to instance 0x8c50af0