iOS 监听键盘变化

　　 //将要显示键盘
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willShowKeyboard:) name:UIKeyboardWillShowNotification object:nil];
    //将要隐藏键盘
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willHideKeyboard:) name:UIKeyboardWillHideNotification object:nil];
    //显示键盘完成
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(DidShowKeyboard:) name:UIKeyboardDidShowNotification object:nil];
    //隐藏键盘完成
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(DidHideKeyboard:) name:UIKeyboardDidHideNotification object:nil];
    //键盘frame将要改变
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidChange:) name:UIKeyboardDidChangeFrameNotification object:nil];
    //键盘frame将要改变
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillChange:) name:UIKeyboardWillChangeFrameNotification object:nil];