NSOperation and NSURLConnection conflicts - iphone

Question

What is the best way to run code on a separate thread?
NSInvocationOperation *operationToComplete = [[NSInvocationOperation alloc] initWithTarget:self selector:#selector(operationMethod) object:nil];
NSOperationQueue *queueToStart=[[NSOperationQueue alloc] init];
[queueToStart addOperation:operationToComplete];
-(void) operationMethod
{
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&_response error:&_error];
}
OR:
NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request
delegate:self];
I've been doing the second way but am little bit confuse regarding this or use another way to do this.

Answer 1

Using operation queues with synchronous requests can be especially useful if you have many concurrent requests that you want to invoke. Operation queues make it easy to not only specify concurrent operation, but also to specify maxConcurrentOperationCount to constrain how many concurrent operations you want to run (which is important if you're firing off a whole bunch of them as you're limited to how many can operate concurrently with a given server).
Your latter example, with initWithRequest, is useful if you need the NSURLConnectionDataDelegate methods (for any of a number of reasons, e.g. you want to update progress view, you want to perform some streaming operations, you want to be able to cancel connection, etc.).
A third approach is to marry the initWithRequest approach with an NSOperationQueue, namely to wrap the NSURLConnection in its own NSOperation. This marries these two techniques, providing the richness of NSURLConnectionDataDelegate methods (cancelable, progress updates, etc.), with the power of operation queues (the ability to add network requests to queue for which you can configure degree of concurrency, establish dependencies between operations, etc.), but providing a nice interface. There are some idiosyncrasies to properly implement this approach (you have to schedule/create a runloop for NSURLConnection if you use it in an NSOperationQueue). I might, therefore, advise using a third party library, such as AFNetworking, if you want to enjoy the richness of this technique without getting lost in the implementation details.
In answer to your question of "which is best", it just depends upon what you're trying to do, as they all have pros and cons. But I prefer a NSOperation-based NSURLConnection, and would generally advise using AFNetworking if you want to simplify your development effort.
By the way, you can probably simplify the first example:
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperationWithBlock:^{
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&_response error:&_error];
}];

Answer 2

Using Grand Central Dispatch (GCD) you can run code in background, which one is easier also.
dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
});
And also NSURLConnection supports two modes of operation: asynchronous and synchronous. Neither uses separate threads at all.