AppDelegate中一些常用方法：
- (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions{
NSLog(@"启动程序，didFinishLaunchingWithOptions");
returnYES;
}
- (void)applicationWillResignActive:(UIApplication*)application
{
NSLog(@"将变为非活跃状态，applicationWillResignActive");
}
- (void)applicationDidEnterBackground:(UIApplication*)application
{
NSLog(@"进入后台，applicationDidEnterBackground");
}
- (void)applicationWillEnterForeground:(UIApplication*)application
{
NSLog(@"由后台进入前台，applicationWillEnterForeground");
}
- (void)applicationDidBecomeActive:(UIApplication*)application
{
NSLog(@"变为活跃状态，applicationDidBecomeActive");
}
- (void)applicationWillTerminate:(UIApplication*)application
{
NSLog(@"程序被杀死，applicationWillTerminate");
}
- (void)application:(UIApplication*)application handleEventsForBackgroundURLSession:(NSString*)identifier completionHandler:(void(^)(void))completionHandler
{
NSLog(@" 应用处于后台，所有下载任务完成调用，handleEventsForBackgroundURLSession");
}
当进入后台，想继续进行操作，如果没有注册后台任务，可实现如下代码：
先定义一个后台任务标识：UIBackgroundTaskIdentifier backgroundTaskIdentifier;
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// 若不实现该代码，进入后台，不会响应定时器事件
backgroundTaskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^(){
// 程序在进入后台一定时间后，我测试是180秒左右，若还未结束后台任务，则会响应该回调，若已结束，则不会进入该回调
NSLog(@"beginBackgroundTaskWithExpirationHandler");
}];
// 这里进行需要的操作，可在操作完成调用endBackgroundTask结束后台任务
[NSTimer scheduledTimerWithTimeInterval:1.f target:self selector:@selector(timerAction) userInfo:nil repeats:YES];
}
- (void)timerAction
{
static int a = 0;
if (a == 100) [self endBackgroundTask];
NSLog(@"a : %d", a++);
}
- (void)endBackgroundTask
{
[[UIApplication sharedApplication] endBackgroundTask:backgroundTaskIdentifier];
backgroundTaskIdentifier = UIBackgroundTaskInvalid;
}
监听进程被杀死时，会发现， 程序处于前台被杀死时会调用applicationWillTerminate:方法，程序处于后台时，并不会调用，需要实现如下代码：
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// 实现如下代码，才能使程序处于后台时被杀死，调用applicationWillTerminate:方法
[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^(){}];
}
- (void)applicationWillTerminate:(UIApplication *)application
{
NSLog(@"程序被杀死，applicationWillTerminate");
}
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