ios app 如何判断home键和返回到前台,willAppear,willDisappear,willEnterForground

上一篇文章提到的设置同步时就有介绍：http://blog.youkuaiyun.com/lanmanck/article/details/38703387

这里单独拿出来说说，参考起来方便快速点。

willAppear,willDisappear一般是View刚启动和多个View切换时会发生，当按下home键时就不会发生了。按下Home时要用通知的方式来掉用一些函数，方法如下：

1、定义进入前台时调用的函数：

- (void)applicationWillEnterForeground:(NSNotification *)notification
{
    //进入前台时调用此函数
}

2、注册调用上面函数的通知，在willAppear中：

- (void)viewWillAppear:(BOOL)animated
{
    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationWillEnterForeground:)
                                                 name:UIApplicationWillEnterForegroundNotification
                                               object:app];
}

3、反注册通知，在willDisappear中：

- (void)viewDidDisappear:(BOOL)animated
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}