1 通过AppDelegate 实现
App进入后台事件方法
- (void)applicationDidEnterBackground:(UIApplication *)application
APP进入前台的事件方法
- (void)applicationWillEnterForeground:(UIApplication *)application
2UIViewController类中通过对Background ，Foreground事件的通知的侦听，进行实现
举例
- (void) viewWillAppear:(BOOL)animated{
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForegroundNotification) name:UIApplicationWillEnterForegroundNotification object:nil];
}
- (void) appWillEnterForegroundNotification{
NSLog(@"trigger event when will enter foreground.");
}
-(void) viewDidDisappear:(BOOL)animated{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
注意：在UIViewController类中viewDidUnload方法在ios6以后过期失效