当应用程序进入后台时，是否可以调用webRequest？

Question

I want to upload images when home button pressed and application goes in background. Is it possible? If yes then how? and if no then do i have any other alternative? Thanks in advance...

Answer 1

You can perform a task in background by using this code for a specific time-

 UIBackgroundTaskIdentifier bgTask = 0;
    UIApplication  *app = [UIApplication sharedApplication];
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        [app endBackgroundTask:bgTask]; 
    }];
    self.silenceTimer = [NSTimer scheduledTimerWithTimeInterval:10 target:self
                                                       selector:@selector(startLocationServices) userInfo:nil repeats:YES];

Refer this: http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html

I think this will help u. :)

Answer 2

An app can request to run in the background for up to 10 minutes after it has been closed so that it can finish a long-running task. Only some processes are allowed to run in background. See Implementing Long-Running Background Tasks section in this reference.

If your app is allowed so, you can try below code:

- (void)applicationDidEnterBackground:(UIApplication *)application

{

    UIBackgroundTaskIdentifier bgTask;
    bgTask = [application beginBackgroundTaskWithExpirationHandler:^{

        // Clean up any unfinished task business by marking where you

        // stopped or ending the task outright.

        [application endBackgroundTask:bgTask];

        bgTask = UIBackgroundTaskInvalid;

    }];



    // Start the long-running task and return immediately.

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{



        // Do the work associated with the task, preferably in chunks.



        [application endBackgroundTask:bgTask];

        bgTask = UIBackgroundTaskInvalid;

    });

}

if you want to know how much time your app has left to run

NSTimeInterval ti = [[UIApplication sharedApplication]backgroundTimeRemaining];
NSLog(@"Remaining Time: %f", ti); // just for debug

For more ref go with this reference PDF(page 60)