获取键盘的高度

- (void)viewDidLoad
{
    [super viewDidLoad];

    //增加监听，当键盘出现或改变时收出消息
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillShow:)
                                                 name:UIKeyboardWillShowNotification object:nil];//注意获取键盘的高度的监听方法，应写在控制器里，若自定义的cell中，有textfield,在自定义的cell中写入监听的话，点击键盘时，第一次点击时高度获取的为0 ，之后再点击才获取到键盘的高度（至于为什么现在还没想清楚）

    //增加监听，当键退出时收出消息
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillHide:)
                                                 name:UIKeyboardWillHideNotification object:nil];

}

//当键盘出现或改变时调用
- (void)keyboardWillShow:(NSNotification *)aNotification
{
    //获取键盘的高度
    NSDictionary *userInfo = [aNotification userInfo];
    NSValue *aValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect keyboardRect = [aValue CGRectValue];
    int height = keyboardRect.size.height;
}

//当键退出时调用
- (void)keyboardWillHide:(NSNotification *)aNotification
{

}