ios-利用键盘通知处理键盘出现时遮挡控件问题

-(void)viewDidLoad {
NSNotificationCenter *center = [NSNotificationCenter defaultCenter];

    //注册键盘显示通知
    [center addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];

    //注册键盘隐藏通知
    [center addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

-(void)viewDidDisappear:(BOOL)animated
{

    //移除通知
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}

- (void) keyboardWillShow:(NSNotification *) notification{

    NSDictionary *info;
    CGSize kbSize;
    double kbheight;
    CGFloat Oversize;
    double duraction;

    info = notification.userInfo;
    kbSize = [[info objectForKey: UIKeyboardFrameEndUserInfoKey]
CGRectValue].size;
    kbheight = kbSize.height;

    Oversize = (self.view.frame.size.height - kbheight) - (textfield.frame.origin.y + textfield.frame.size.height+);

    duraction =  [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];

    if (Oversize < ){
        [UIView animateWithDuration: duraction animations:^{
            self.view.frame = CGRectMake(0.0f, Oversize, self.view.frame.size.width, self.view.frame.size.height);
        }];
    }
}

-(void) keyboardWillHide:(NSNotification *) notification{

    double duraction = [[notification.userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];

    [UIView animateWithDuration:duraction animations:^{
        self.view.frame = CGRectMake(, , self.view.frame.size.width, self.view.frame.size.height);
    }];
}