NSURLConnection and multitasking in iOS

问题:

I'm using NSURLConnection to download resources asynchronously in iOS. (They are large-ish PDF files, so it takes some time on a slow connection.)

Now I'm updating my app from iOS 3 to iOS 4. As my app is none of location-aware, voip, and background music, I guess I need to do something.

My question is, then, what happens to the NSURLConnection currently running? Is it suspended and magically resumed when the app comes back to the foreground, or is it outright killed? If it is the latter, what is the standard strategy to resume it automatically later? Is there a open-source subclass of NSURLConnection which automatically does that?

回答1:

You can start a task that will run for at most 10 minutes. Look at using the beginBackgroundTaskWithExpirationHandler: API for this purpose. Just be aware, if your task takes too long, it will be killed by the OS.

回答2:

The NSURLConnection is indeed suspended and started again when the app enters the foreground. Just make sure you kill the connection if the app moves from suspended to not running like so:

- (void)applicationWillTerminate:(UIApplication *)application {
    if (self.downloadConnection != nil){
        [self.downloadConnection cancel];
    }
}