问题
Is it possible to download a file while the app is in background in iPhone 4?
回答1:
Under iOS 4.x, you can use request some background time using UIApplication beginBackgroundTaskWithExpirationHandler: and perhaps continue a file download for a limited period of time.
See Apple's document on "multitasking" background execution for details.
回答2:
Yes, it is.
It's supported in ASIHTTPRequest as of v1.8:
http://allseeing-i.com/ASIHTTPRequest/How-to-use#background_downloads_ios
(There was also an experimental branch of v1.7 with it at http://github.com/pokeb/asi-http-request/commits/backgroundtask but this appears not to exist anymore.)
It's also supported in AFNetworking, see Does AFNetworking have backgrounding support?
来源：https://stackoverflow.com/questions/3612963/download-in-background-in-iphone