JSON requests in iOS - use Grand Central Dispatch or NSURLConnection

Question

I saw several tutorials on making JSON requests in iOS, many of them listed something like this using NSURLConnection:

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [self.responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog([NSString stringWithFormat:@"Connection failed: %@", [error description]]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {}

But I read another tutorial today (http://mobile.tutsplus.com/tutorials/iphone/ios-quick-tip-interacting-with-web-services/) where it had this beautifully simple implementation:

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
    NSError *error = nil;
    NSURL *url = [NSURL URLWithString:@"http://brandontreb.com/apps/pocket-mud-pro/promo.json"];
    NSString *json = [NSString stringWithContentsOfURL:url
                                              encoding:NSASCIIStringEncoding
                                                 error:&error];
    NSLog(@"\nJSON: %@ \n Error: %@", json, error);
});

Which one would be better to use? Is there one inherently wrong with the simplicity of the latter?

The second is simpler and probably harder to muck up, especially if you're juggling a lot of requests. Not quite a flexible as the first. — Hot Licks, Mar 23 '13 at 20:36

score 7 · Accepted Answer · answered Mar 23 '13 at 20:21

There is nothing "wrong" with the using stringWithContentsOfURL:encoding:error: but you have no flexibility in how you handle a request in progress. If you need to do any of the following then I would use NSURLConnection:

display a completion % to users during a request
perform a request to a host requiring HTTP authentication
more complicated data handling (e.g. downloading more data than a typical JSON response from a web service) where you may want to handle the response in chunks
cancel the request (thanks @martin)

4. You can cancel the request. – Martin R Mar 23 '13 at 20:23 — Martin R, Mar 23 '13 at 20:23

score 1 · Answer 2 · answered Mar 23 '13 at 20:20

1

Use the first one. You have a method which is telling you when the connection has finished, then you can perform another method to display the data or whatever you plan on doing with it.

answered Mar 23 '13 at 20:20

Kris Gellci

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`stringWithContentsOfURL:encoding:error:` is synchronous so when it returns the request is complete. You can then post a notification to the main thread to display the result in UI. There are other reasons why I prefer `NSURLConnection` however. – XJones Mar 23 '13 at 20:23
It is true, you can do that, but it is simpler to use something built with delegate methods that let you know when completion has occurred. – Kris Gellci Mar 23 '13 at 20:26

JSON requests in iOS - use Grand Central Dispatch or NSURLConnection

2 Answers2

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