Continue download in background

问题:

I am creating an application wherein I am downloading some data from server. While going in background I want that connection should continue running so that data can be downloaded. I know there is method in appDelegate

- (void)applicationDidEnterBackground:(UIApplication *)application  

which is called when application enters background. But as the connection is created in viewController, how can it be managed in appDelegate?
Also is/are there other way(s) this can be done? I have gone through this link but is there a something simple to implement?

回答1:

One way to do some operations that continue in the background is to create a separate thread to do the downloading. Inside the thread, bracket your download operations between calls to beginBackgroundTaskWithExpirationHandler: and endBackgroundTask. You don't need to check to see whether you are running in the background or not, you just always call these two methods.

// Tell iOS this as a background task in case we get backgrounded
UIBackgroundTaskIdentifier taskId = [[UIApplication sharedApplication] 
          beginBackgroundTaskWithExpirationHandler:NULL];

//----------------------------------------------
// Perform your download operations here
//----------------------------------------------
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];

// Tell iOS that we are done with stuff that needed to keep going even if backgrounded    
[[UIApplication sharedApplication] endBackgroundTask:taskId];

回答2:

[edit] Sorry I was incorrect, as was pointed out in the comments you can extend the time limit you have to perform operations once/before your app goes into the background. Here is Apple's Official Documentation

回答3:

I don't know how you handle your data downloading exactly. But you can take a look at ASIHTTPRequest. It is very simple and straightforward, and works with ARC if you set the compiler flags to -fno-objc-arc. With this you only have to use

ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setShouldContinueWhenAppEntersBackground:YES]; //For iOS 4.0 and up 

And that works.

Here you can see how ASIHTTPRequest works

Hope it helps!