UIApplicationDelegate协议

// app接收到内存警告时调用

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application;

// app进入后台时调用（比如按了home键）

- (void)applicationDidEnterBackground:(UIApplication *)application;

// app启动完毕时调用

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;

Application系统事件

程序加载完毕 application: didFinishLaunchingWithOptions:

程序获取焦点 applicationDidBecomeActive:

程序进入后台 applicationDidEnterBackground:

程序失去焦点 applicationWillResignActive:

程序从后台回到前台 applicationWillEnterForeground:

内存警告 applicationDidReceiveMemoryWarning:

程序即将退出 applicationWillTerminate: