Question

I need to make some POST calls to my server, but I need to not block the main thread. As I understand, NSMutableURLRequest and NSURLConnection are not thread safe, so it is best to use the async method of NSURLConnection.

My question about this is, how I can package it up nicely into a method, instead of having to use the delegate method? I would prefer to do:

NSData *returnedData = [Utility postDataToURL:@"some string of data"];

This is how it is easy done with the following method:

[NSURLConnection sendSynchronousRequest:serviceRequest returningResponse:&serviceResponse error:&serviceError];

It is so nice keeping everything within one method, then just having my data returned from it!

Are there any block based methods for this? It becomes an issue when I need to write methods for about 50 different calls and each one needs to use the same delegate method. Am I going about this the wrong way?

This will only need to be for iOS5.

Answer 1

iOS 5 adds sendAsynchronousRequest:queue:completionHandler: which does what I think you want. I’ve got my code set up to use that if available, but to fall back on performing a synchronous fetch on a background GCD queue and hopping onto the main thread with the result if it doesn’t. The latter will be less power efficient but it’s just to maintain legacy support.

if([NSURLConnection respondsToSelector:@selector(sendAsynchronousRequest:queue:completionHandler:)])
{
    // we can use the iOS 5 path, so issue the asynchronous request
    // and then just do whatever we want to do
    [NSURLConnection sendAsynchronousRequest:request
        queue:[NSOperationQueue mainQueue]
        completionHandler:
        ^(NSURLResponse *response, NSData *data, NSError *error)
        {
            [self didLoadData:data];
        }];
}
else
{
    // fine, we'll have to do a power inefficient iOS 4 implementation;
    // hop onto the global dispatch queue...
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
    ^{
        // ... perform a blocking, synchronous URL retrieval ...
        NSError *error = nil;
        NSURLResponse *urlResponse = nil;
        NSData *responseData =
            [NSURLConnection sendSynchronousRequest:request returningResponse:&urlResponse error:&error];

        // ... and hop back onto the main queue to handle the result
        dispatch_async(dispatch_get_main_queue(),
        ^{
            [self didLoadData:responseData];
        });
    });
}

In production code you’d actually check the errors and HTTP response codes (as a server 404 response is probably just as much an error from your point of view as a connection failure), obviously.