如何解决iOS后台应用程序提取不起作用？

>我的测试设备正在运行iOS 9.3.5(我的部署目标是7.1)
>我在Xcode中的目标“功能”下的“后台模式”下启用了“后台提取”功能

在应用程序：didFinishLaunchingWithOptions我已经尝试过各种间隔与setMinimumBackgroundFetchInterval，包括UIApplicationBackgroundFetchIntervalMinimum

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

    // tell the system we want background fetch
    //[application setMinimumBackgroundFetchInterval:3600]; // 60 minutes
    [application setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];
    //[application setMinimumBackgroundFetchInterval:1800]; // 30 minutes

    return YES;
}

我已经实现了应用程序：performFetchWithCompletionHandler

void (^fetchCompletionHandler)(UIBackgroundFetchResult);
NSDate *fetchStart;

-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
    fetchCompletionHandler = completionHandler;

    fetchStart = [NSDate date];

    [[NSUserDefaults standardUserDefaults] setObject:fetchStart forKey:kLastCheckedContentDate];
    [[NSUserDefaults standardUserDefaults] synchronize];

    [FeedParser parseFeedAtUrl:url withDelegate:self];
}

 -(void)onParserFinished
{
    DDLogVerbose(@"AppDelegate/onParserFinished");

    UIBackgroundFetchResult result = UIBackgroundFetchResultNoData;

    NSDate *fetchEnd = [NSDate date];
    NSTimeInterval timeElapsed = [fetchEnd timeIntervalSinceDate:fetchStart];
    DDLogVerbose(@"Background Fetch Duration: %f seconds",timeElapsed);
    if ([self.mostRecentContentDate compare:item.date] < 0) {
        DDLogVerbose(@"got new content: %@",item.date);
        self.mostRecentContentDate = item.date;
        [self scheduleNotificationWithItem:item];
        result = UIBackgroundFetchResultNewData;
    }
    else {
        DDLogVerbose(@"no new content.");
        UILocalNotification* localNotification = [[UILocalNotification alloc] init];
        localNotification.fireDate = [NSDate dateWithTimeIntervalSinceNow:60];
        localNotification.alertBody = [NSString stringWithFormat:@"Checked for new posts in %f seconds",timeElapsed];
        localNotification.timeZone = [NSTimeZone defaultTimeZone];
        [[UIApplication sharedApplication] scheduleLocalNotification:localNotification];
    }

    fetchCompletionHandler(result);
}

>我有(成功！)测试与模拟器和设备使用Xcode的Debug / SimulateBackgroundFetch
>我已经通过另一个SO答案(http://stackoverflow.com/a/29923802/519030)所示的新计划成功测试了
>我的测试显示执行在performFetch方法的代码大约0.3秒(所以它不需要很长时间)
>我已经验证设备在设置中启用了后台刷新功能。
>当然，我已经看过其他的SO问题，希望有人经历过同样的事情。

（编辑：李大同）

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