NSOperation队列在后台不起作用

Question

I want that my image uploading should work in background . I have enable Background Modes and made a Operation queue to upload multiple files at a time to server. But as soon as put app in background NSOperation pauses, and restart again when in foreground. I have also added beginBackgroundTaskWithExpirationHandler before starting my operation queue and endBackgroundTask when all images get uploaded in server.

This makes all images upload to server also while app is in background, but my app is getting killed, I don't want the app to get killed .

Please suggest some solution to my problem .

Answer 1

Your app has limited time when running in background. After its allotted time has expired it gets killed.

According to Apple:

In your own expiration handlers, you can include additional code needed
to close out your task. However, any code you include must not take too 
long to execute because, by the time your expiration handler is called,
your app is already very close to its time limit. For this reason,
perform only minimal cleanup of your state information and end the
task.

Also get the value of the backgroundTimeRemaining property to check the remaining time.