1. 定义一个方法
update
2. [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(update) name:@"update" object:nil]
3. 在要发出通知消息的地方
[[NSNotificationCenter defaultCenter] postNotificationName:@"update" object:nil];
come from http://blog.csdn.net/dadalan/archive/2009/06/08/4252484.aspx