Using NSURLSessionDataTask, can I resume downloading a file, even if user comes back after quitting an App?

Question

Suppose, I am downloading a file of 300 MB using NSURLSessionDownloadTask or NSURLSessionDataTask (at present, I don’t know which is the best choice in my case). User quits the App or App suddenly crashed while 250 MB were downloaded. When next time, when user opens the App, I would have to resume downloading from 250 MB.

I have made a demo using NSURLSessionDownloadTask. But, if we are using NSURLSessionDownloadTask, we don't have access to the NSURL of the temporary file until the download is complete (and in didFinishDownloadingToURL we would move this temporary file to its permanent final location).

I came to know that, I will have to use an NSURLSessionDataTask rather than a DownloadTask, then use the delegate method on NSURLSessionDataDelegate:

- (void)URLSession:(NSURLSession *)session
      dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data;

This will allow me to access the data as it is received. But, I don’t know how would I manage things now onward. I want a way, so that I can append data in above delegate and write it on disk at some location. Second question, how would I know that the downloading of a data should start from here only (i.e. from 250 MB)

Is it really feasible? Or it is feasible only if the App is in active state?

I am desperate to this question.