KVO与KVC

 [_receivedData setValue:@"moxue" forKey:@"name"];//修改值
 [_receivedData valueForKey:@"name"];//查看值

    [[NSUserDefaults standardUserDefaults]setValue:@"myname" forKey:@"myname"];//设置键值
    [[NSUserDefaults standardUserDefaults] addObserver:self forKeyPath:@"myname" options:NSKeyValueObservingOptionNew context:nil];//对其进行键值观察，通过设置NSKeyValueObservingOptionNew参数，设置观察的值为最新数据
    [[NSUserDefaults standardUserDefaults] setValue:@"haha" forKey:@"myname"];//改变键值对


-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
    //keyPath为键值的Key，change参数储存改变的值的字典。
    if ([keyPath isEqualToString:@"myname"]) {
        NSLog(@"%@",[change valueForKey:@"new"]);//取出NSKeyValueObservingOptionNew最新数据。
    }
}