iOS 后台进入前台和进入后台通知

1. 注册通知

//后台进前台通知 UIApplicationDidBecomeActiveNotification
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didBecomeActive) name:UIApplicationDidBecomeActiveNotification object:nil];

//进入后台UIApplicationDidEnterBackgroundNotification
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];

2. 实现通知方法

//进入后台方法
- (void)didEnterBackground {
    NSLog(@"%@", NSStringFromSelector(_cmd));
}

//每次后台进前台都会执行这个方法
- (void)didBecomeActive {
    NSLog(@"%@", NSStringFromSelector(_cmd));
}

3. 移除通知

- (void)dealloc {
    [[NSNotificationCenter defaultCenter]removeObserver:self]; //移除通知
}