ios - 后台模式在iOS 8中不起作用

Question

在我的应用程序中，我每分钟都会从服务器获取更新。对于后台，我正在使用代码

 UIApplication*  app = [UIApplication sharedApplication];
 bti = [app beginBackgroundTaskWithExpirationHandler:^{

    NSLog(@"Debug - Ending background task %d",bti);
    [app endBackgroundTask:bti];
    NSLog(@"Debug -  Background task %d ended",bti);
    bti = UIBackgroundTaskInvalid;

}];
NSLog(@"Debug - Starting background task %d",bti);

[NSTimer scheduledTimerWithTimeInterval:60.0 target: self
                               selector: @selector(anyTask) userInfo:nil repeats: YES];

但是应用程序在一段时间后终止并获取日志

{(
    <BKProcessAssertion: 0x15ddbf50> identifier: Background Content Fetching (79) process: DemoApp[628] permittedBackgroundDuration: 30.000000 reason: backgroundContentFetching owner pid:33 preventSuspend  preventThrottleDownUI  preventIdleSleep  preventSuspendOnSleep 
)}

我还使用了这样的背景获取:

-(void)application:(UIApplication *)application
    performFetchWithCompletionHandler:
     (void (^)(UIBackgroundFetchResult))completionHandler {
NSLog(@"Background fetch started...");
  [self repeatTask];
//    //---do background fetch here---


NSLog(@"Background fetch completed...");

}

任何帮助，将不胜感激 :)

Answer 1

您不能使用此技术无限期地在后台运行。您可以使用后台获取模式来允许您的应用轮询服务器(但频率为分钟或几小时)，也可以让服务器使用推送通知来提醒您的应用有新内容。您当前的方法对电池不太友好

如果要使用后台获取模式，则需要以适当的结果调用提供的completionHandler-

completionHandler(UIBackgroundFetchResultNewData);

要么

completionHandler(UIBackgroundFetchResultNoData);

要么

completionHandler(UIBackgroundFetchResultFailed);

在performFetchWithCompletionHandler:的末尾

例如

-(void)application:(UIApplication *)application
    performFetchWithCompletionHandler:
     (void (^)(UIBackgroundFetchResult))completionHandler {
         NSLog(@"Background fetch started...");
         if ([self repeatTask]) { // //---do background fetch here--- returns YES if new data
             completionHandler(UIBackgroundFetchResultNewData);
         }
         else {
             completionHandler(UIBackgroundFetchResultNoData);
         }
         NSLog(@"Background fetch completed...");
}