//UIApplicationDelegate以下的方法都是实现了前面这个协议的- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    // Override point for customization after application launch.    //完成应用初始化后需要执行的函数    NSLog(@"应用初始化完成");    return YES;}                            - (void)applicationWillResignActive:(UIApplication *)application{    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.   NSLog(@"应用即将进入后台,意思就是进入后台失去活动状态");}- (void)applicationDidEnterBackground:(UIApplication *)application{    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.     // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.      NSLog(@"应用进入后台,先失去活跃状态再调用这个");}- (void)applicationWillEnterForeground:(UIApplication *)application{     NSLog(@"应用即将进入前台，先进入前台再到活跃状态");        // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.}- (void)applicationDidBecomeActive:(UIApplication *)application{     NSLog(@"应用进入前台，获得活跃状态");    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.}- (void)applicationWillTerminate:(UIApplication *)application{      NSLog(@"终止函数");//程序关闭的时候被调用    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.}- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application{    //出现内存警告的时候调用}