�uiview不用通知，一般都用代理来解决，能用代理解决的，坚持不用通知

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UIView中哪个方法注册通知比较好(动态获取键盘高度)

-(void)layoutSubviews
{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWasShown:) name:UIKeyboardDidShowNotification object:nil];

    [[NSNotificationCenter defaultCenter]  addObserver:self selector:@selector(keyboardWasHidden:) name:UIKeyboardDidHideNotification object:nil];
}
- (void) keyboardWasShown:(NSNotification *) notif
{
    NSDictionary *info = [notif userInfo];
NSValue *value = [info objectForKey:UIKeyboardFrameBeginUserInfoKey];
    CGSize keyboardSize = [value CGRectValue].size;

    kHeight = keyboardSize.height;
    NSLog(@"keyBoard:%f", keyboardSize.height);  //216
///keyboardWasShown = YES;
}
- (void) keyboardWasHidden:(NSNotification *) notif
{
    NSDictionary *info = [notif userInfo];

NSValue *value = [info objectForKey:UIKeyboardFrameBeginUserInfoKey];
    CGSize keyboardSize = [value CGRectValue].size;
    kHeight = keyboardSize.height;
NSLog(@"keyboardWasHidden keyBoard:%f", keyboardSize.height);
// keyboardWasShown = NO;