iOS应用的程序状态

正常启动一个app时

1. not running: app未启动时处于未运行状态
2. inactive: 启动app后进入未激活状态
   • application:willFinishLaunchingWithOptions: 应用启动未进入状态保存的回调
   • application:didFinishLaunchingWithOptions: 基本的准备已经完成，可以启动的回调
3. active: 激活状态
   • applicationDidBecomeActive: app已经切换到active状态后的回调

切换到后台再切换到前台

1. active -> inactive
   • applicationWillResignActive: app将要从前台切换到后台的回调
2. background: 后台状态
   • applicationDidEnterBackground: app已经进入后台的回调
3. inactive -> active
   • applicationWillEnterForeground: app将要从后台切换到前台的回调
   • applicationDidBecomeActive: app已经切换到active状态后的回调

来回切换应用/锁屏解锁

• 换到另一个app/锁屏：由状态active切换到inactive，此时调用applicationWillResignActive
• 换到此app/解锁：由状态inactive切换到running，此时调用applicationDidEnterBackground

应用终止

• applicationWillTerminate: app将要结束时的回调

使用应用状态的回调

在AppDelegate中使用

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- (void)applicationDidEnterBackground:(UIApplication *)application {
    NSLog(@"进入后台");
}
- (void)applicationWillEnterForeground:(UIApplication *)application {
    NSLog(@"进入前台");
}

使用通知

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[[NSNotificationCenter defaultCenter]addObserver:self 
    selector:@selector(enterBackground)
    name:UIApplicationDidEnterBackgroundNotification
    object:nil];

- (void)enterBackground{
    NSLog(@"进入后台");
}

[[NSNotificationCenter defaultCenter]addObserver:self 
    selector:@selector(enterForeground) 
    name:UIApplicationDidBecomeActiveNotification 
    object:nil];

- (void)enterForeground{
    NSLog(@"回到app");
}