Asynchronous network operations in iOS 5 - objective-c

Question

Everywhere I look, I see people explicitly using queues or run loops to do network operations. Should I still do that in iOS 5, or should I use NSURLConnection sendAsynchronousRequest:queue:completionHandler: instead? Is this the preferred method of doing network operations in iOS >= 5?

Answer 1

I can't answer for others' preference, but I rolled my own < os5, and I strongly prefer the block operation. a) I'm never interested in intermediate results of the network operation, or the repetitive code to handle them, b) the block is retained, so I get fewer race conditions where some aspect of the delegate gets prematurely released, and c) I never get mixed up about what code is running when a particular operation finishes.
In short, it's a huge improvement in the NSURLConnection interface, IMO.

Answer 2

It depends. For simple things, the new block-based API makes life a lot easier. However, compared to implementing the NSURLConnectionDelegate methods, you lose some control.
For example, it's not possible to cancel connections that have been initiated with this method, or to handle the response (e.g. for parsing headers) before all data is downloaded.

Answer 3

You can do something similar to this with iOS 4 as well using GCD.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
NSData *data = [NSURLConnection sendSynchronousRequest:blah returningResponse:response error:blah];
//process response body here
dispatch_async(dispatch_get_main_queue(), ^{
//Update UI Code here
self.textView.text = [[NSString alloc] initWithData:data];
});
});
The problem with this code and the code OP posted is that, once the connection is made, you cannot cancel them.
Canceling a request on viewDidDisappear goes a long way in improving the performance of your application. I talk extensively about this on the book iOS PTL
Second reason why you need a third party networking framework like MKNetworkKit or RestKit or the now defunct ASIHTTP is for authentication. Most web service require that you authenticate using a NSURLCredential (HTTP Basic or HTTP Digest or Windows NTLM or oAuth)
This alone will take a couple of days to do if you roll out your own code. Not that you shouldn't do it. But there is no need for one as all these third party frameworks are extensively used and the chances or bugs or performance issues in them is less compared to your own code.

Answer 4

I've written a blog post that compares several approaches including NSURLConnection, AFNetworking, and ReactiveCocoa.
ReactiveCocoa approach
If you want to get really fancy with asynchronous network calls, you can try out ReactiveCocoa. ReactiveCocoa allows you to define signals that represent each of your network requests. And it allows you to chain multiple dependent network calls.
#import <ReactiveCocoa/ReactiveCocoa.h>
// ...
-(RACSignal*)signalGetNetworkStep1 {
NSURL* url = ...;
return [RACSignal createSignal:^(RACDisposable *(id subscriber) {
NSURLRequest *request1 = [NSURLRequest requestWithURL:url];
AFJSONRequestOperation *operation1 = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
[subscriber sendNext:JSON];
[subscriber sendCompleted];
} failure:^(AFHTTPRequestOperation *operation, NSError *error){
[subscriber sendError:error];
}];
[operation1 start];
return nil;
}
}
-(void) yourMethod {
[[self signalGetNetworkStep1] subscribeNext:^(id *x) {
// perform your custom business logic
}];
}