记录一些容易忘记的属性 -- UIKeyboard

    //UIKeyboardWillShowNotification这个通知在软键盘弹出时由系统发送
    //UIKeyboardWillShowNotification 通知：键盘将要显示的通知
    //在通知中心中添加监测对象，当该对象受到UIKeyboardWillShowNotification的通知时，会调用参数二所代表的方法
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];