iOS全局处理键盘事件

1. 注册监听键盘事件的通知
   

       [[NSNotificationCenter defaultCenter] addObserver:self
                                                selector:@selector(keyboardWillShow:)
                                                    name:UIKeyboardWillShowNotification
                                                  object:nil];
       
       [[NSNotificationCenter defaultCenter] addObserver:self
                                                selector:@selector(keyboardShow:)
                                                    name:UIKeyboardDidShowNotification
                                                  object:nil];
       
       [[NSNotificationCenter defaultCenter] addObserver:self
                                                selector:@selector(keyboardWillHide:)
                                                    name:UIKeyboardWillHideNotification
                                                  object:nil];
       
       [[NSNotificationCenter defaultCenter] addObserver:self
                                                selector:@selector(keyboardHide:)
                                                    name:UIKeyboardDidHideNotification
                                                  object:nil];

2. 在键盘将要出现和隐藏的回调中，加入动画。
   

   - (void)keyboardWillShow:(NSNotification *)notif {
       if (self.hidden == YES) {
           return;
       }
       
       CGRect rect = [[notif.userInfo objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
       CGFloat y = rect.origin.y;
       [UIView beginAnimations:nil context:nil];
       [UIView setAnimationDuration:0.25];
       NSArray *subviews = [self subviews];
       for (UIView *sub in subviews) {
           
           CGFloat maxY = CGRectGetMaxY(sub.frame);
           if (maxY > y - 2) {
               sub.center = CGPointMake(CGRectGetWidth(self.frame)/2.0, sub.center.y - maxY + y - 2);
           }
       }
       [UIView commitAnimations];
   }
   
   - (void)keyboardShow:(NSNotification *)notif {
       if (self.hidden == YES) {
           return;
       }
   }
   
   - (void)keyboardWillHide:(NSNotification *)notif {
       if (self.hidden == YES) {
           return;
       }
       [UIView beginAnimations:nil context:nil];
       [UIView setAnimationDuration:0.25];
       NSArray *subviews = [self subviews];
       for (UIView *sub in subviews) {
           if (sub.center.y < CGRectGetHeight(self.frame)/2.0) {
               sub.center = CGPointMake(CGRectGetWidth(self.frame)/2.0, CGRectGetHeight(self.frame)/2.0);
           }
       }
       [UIView commitAnimations];
   }
   
   - (void)keyboardHide:(NSNotification *)notif {
       if (self.hidden == YES) {
           return;
       }
   }