在iPhone上执行后台任务

当App进入到后台时，可以有一段时间做处理工作。

或者，对于某些服务，可以长时间运行，比如播放音乐。

对于长时间运行的任务，需要在Info.plist添加一行，键为UIBackgroundModes，值为一个数组，可以包含如下几个字符串：

audio
location
voip
newsstand-content
external-accessory
bluetooth-central



然后，在后台就可以做一些事情了：

[cpp] view
plaincopy

- (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.

UIDevice *device = [UIDevicecurrentDevice];

BOOL backgroundSupported = NO;

if ([device respondsToSelector:@selector(isMultitaskingSupported)]) {

backgroundSupported = YES;

}

__blockUIBackgroundTaskIdentifier bgTaskId = [application beginBackgroundTaskWithExpirationHandler:^{

[application endBackgroundTask:bgTaskId];

bgTaskId = UIBackgroundTaskInvalid;

}];

if (backgroundSupported) {

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

//

});

}

}