理解允许定位,音频,网络电话..

大家都知道我们的程序在后台运行的时间是10分钟，10分钟后便会停止。但是像实时定位，播放音频，以及网络电话这些功能我们需要在后台持续运行。那么我们就要进行相应的设置。

- (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.
    */

    if ([[UIDevice currentDevice] respondsToSelector:@selector(isMultitaskingSupported)])
    { //Check if our iOS version supports multitasking I.E iOS 4
        if ([[UIDevice currentDevice] isMultitaskingSupported])
        { //Check if device supports mulitasking
            UIApplication *application = [UIApplication sharedApplication];
            //Get the shared application instance  

            __block UIBackgroundTaskIdentifier background_task;
            //Create a task object  

            background_task = [application beginBackgroundTaskWithExpirationHandler: ^{
                /*
                 当应用程序后台停留的时间为0时，会执行下面的操作
                 （应用程序后台停留的时间为600s，可以通过backgroundTimeRemaining查看）
                 */
                [application endBackgroundTask: background_task];
                 //Tell the system that we are done with the tasks
                background_task = UIBackgroundTaskInvalid;
                //Set the task to be invalid  

                //System will be shutting down the app at any point in time now
            }];  

            // Background tasks require you to use asyncrous tasks  

            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                //Perform your tasks that your application requires
                NSLog(@"time remain:%f", application.backgroundTimeRemaining);
                [application endBackgroundTask: background_task];
                //End the task so the system knows that you are done with what you need to perform
                background_task = UIBackgroundTaskInvalid; //Invalidate the background_task
            });
        }
    }
}

修改应用的Info.plist 文件，你需要在Info.plist文件中添加UIBackgroundModes字段，该字段的值是应用支持的所有后台模式，是一个数值类型。目前此数 组可以包含“audio”、“location”和“voip”这三个字符串常量.