iOS Application Background Downloading - iphone

Question

Hey! I need to know how I can have my iOS Application start a download in the background of the application (like, have the download run in the AppDelegate file) so changing ViewControllers will not interrupt or cancel the download. I also need to be able to get the progress of the download (0.00000 - 1.00000), to set a UIProgressView object to, which also means I need a - (void)progressDidChangeTo:(int)progress function.

Answer 1

Just use ASIHTTPRequest it is way easier than NSURLRequest and does exactly what you need.
It examples that shows how to download in background and how to report progress.
I wouldn't download anything in the AppDelegate directly. Instead I would create a separated class just for that purpose. Let's call it MyService I would then initialize that class in my app delegate.
The class can work as a singleton or can be passed to each view controller that requires it.
In MyService class I would add the ASINetworkQueue and few methods to handle the requests when they are ready. Here is the code from ASI examples that you can use:
- (IBAction)startBackgroundDownloading:(id)sender
{
if (!self.queue) {
self.queue = [[[ASINetworkQueue alloc] init] autorelease];
}
NSURL *url = [NSURL URLWithString:#"http://allseeing-i.com"];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[request setDidFinishSelector:#selector(requestDone:)];
[request setDidFailSelector:#selector(requestWentWrong:)];
[self.queue addOperation:request]; //queue is an NSOperationQueue
[self.queue go];
}
- (void)requestDone:(ASIHTTPRequest *)request
{
NSString *response = [request responseString];
//Do something useful with the content of that request.
}
- (void)requestWentWrong:(ASIHTTPRequest *)request
{
NSError *error = [request error];
}
If you need to set the progress bar. I would just expose the setDownloadProgressDelegate of ASINetworkQueue in my MyService class and set it in my ViewControllers like that:
[[MyService service] setDownloadProgressDelegate: self.myUIProgressView];
BTW. If you need to continue downloading even when your app exits you can set ShouldContinueWhenAppEntersBackground property of your request to YES.

Answer 2

you can use NSURLConnection to start an asynchronous request that won't cause your UI to be frozen. You can do it by doing something like:
NSURLRequest *urlRequest = [[NSURLRequest alloc] initWithURL:url];
connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];
[urlRequest release];
in order to have your progress you can use the:
connection:didReceiveResponse:(NSURLResponse *)response;
delegate call to inspect the response.expectedContentLength and then use the
connection:didReceiveData:(NSData *)data
to track the amount of data that was downloaded and calculate a percentage.
Hope this helps,
Moszi