I am trying to make sure that if my background download on iOS stops for whatever reason (app is killed by the system, stopped by the user from the multitasking screen, crash?) will continue in the next lifecycle. So far I have found that the documentation for NSURLSession clearly differentiates between two clear use cases: terminated by the system ( in which case downloads will continue smoothly in the background and the system will wake up the application when the download finishes ) or killed by user (and which case everything is lost - or is it? ):
If an iOS app is terminated by the system and relaunched, the app can use the same identifier to create a new configuration object and session and retrieve the status of transfers that were in progress at the time of termination. This behavior applies only for normal termination of the app by the system. If the user terminates the app from the multitasking screen, the system cancels all of the session’s background transfers. In addition, the system does not automatically relaunch apps that were force quit by the user. The user must explicitly relaunch the app before transfers can begin again.
This is the line that bugs me. What transfers can begin again? I thought they were lost. Does it refer to the fact that I can start another download session?
Also, I could not find any info on what happens with downloads that are suspended by the system because of the network connection type. For instance if allowsCellularAccess is set to false, and my app is terminated by the system, will it still continue when it moves to an allowed network?
