键盘弹出和收起的通知

//订阅键盘升起的系统通知     

UILabel * label = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 220* 2, 30)];

在 - (void)viewDidLoad写下面的代码   

[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(keyboardWillshow) name:UIKeyboardWillShowNotification object:nil];         [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(keyboardWillHide) name:UIKeyboardWillHideNotification object:nil];     } -(void)keyboardWillshow {  

  [UIView animateWithDuration:0.2 animations:^{    

    _butn.frame = CGRectMake(20, 20, 200, 20);

//这里写butn要改变的位置   

} completion:^(BOOL finished) {        

    }];

}

-(void)keyboardWillHide {   

[UIView animateWithDuration:0.2 animations:^{   

     _butn.frame = CGRectMake(20, 20, 200, 20);//这里写butn刚开始定义的原位置     } completion:^(BOOL finished) {   

         }];

}

}