NSNotificationCenter消息通信(KVO)

NSNotificationCenter是程序不同类间的消息通信.

注册消息通知:

    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(mthMsg:) name:@"mthMsg" object:nil]; 

addObserver:　注册通知

selector:　收到通知后调用何种方法;

name：　通知的名字(唯一标示)。

发送消息通知:

 [[NSNotificationCenter defaultCenter] postNotificationName:@"mthMsg"　object:obj];

  postNotificationName：消息的名称  

//键盘注册通知
1 //键盘升起
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
 //键盘降下
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];