Question

I’m trying to download some files using NSURLConnection:

- (void)startDownload {
  NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
  [req addValue:@"Basic XXXXXXXXXXXXXX=" forHTTPHeaderField:@"Authorization"];
  connection = [[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse*)response {
  filepath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:save_name];
  [[NSFileManager defaultManager] createFileAtPath:filepath contents:nil attributes:nil];
  file = [[NSFileHandle fileHandleForUpdatingAtPath:filepath] retain];
  [file seekToEndOfFile];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
  [file seekToEndOfFile];
  [file writeData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection*)connection {
  [file closeFile];
 }

My files are quite big, so I have to save every piece I download to a disk, can’t store them in RAM. The question is, how can I handle multiple downloads?

I was thinking to start the next download after the previous one is finished in - (void)connectionDidFinishLoading:, but I guess it is not the best way to do it. Any suggestions?

Answer 1

If you want to use NSURLConnection I would recommend making your own download object that wraps the connection and deals with writing it to disk.

You would initialise your object with a filename to put the finished file in and the URL to get the file from, something like :

MyDownloadObject *o = [[MyDownloadObject alloc] initWithFilename:filename URL:url];
o.delegate = self;

Each download object would deal with it’s own NSURLRequest and NSURLConnection, using pretty much the same code as in your question 🙂

When it’s finished it would tell your view controller that it’s downloaded (probably via a delegate method but a notification would work just as well). You can then tell from the delegate method which file has finished.

- (void)myDownloadObjectFinishedDownload:(MyDownloadObject *)o {
    NSLog(@"File from %@ has been stored at %@", o.URL, o.filename);
}

If you made your MyDownloadObject a subclass of NSOperation then you could use an NSOperationQueue to limit the concurrent downloads and monitor overall progress etc.

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If you didn’t mind using a third party library then ASIHTTPRequest is a good choice but be warned, it’s not being developed anymore. I suspect that other people on stack overflow will recommend better, more up to date, libraries you could use instead.