Sharing NSOperationQueue across View Controllers?

Question

I\'m using an NSOperationQueue to manage HTTP connections (using ASI-HTTPRequest). Since I have multiple views and the need to have these different views requesting HTTP connect

Answer 1

My personal preference for this is to have a singleton that manages all http requests. Each view would then ask the singleton to make the http call, passing itself as a delegate for that call then the singleton hands that delegate and call off to an NSOperation and then NSOperation calls back once the call is done.

Answer 2

I have solved this by adding a class method on NSOperationQueue that I think Apple has missed; a shared operation queue. I add this as a category on NSOperationQueue as this:

// NSOperationQueue+SharedQueue.h
@interface NSOperationQueue (SharedQueue)
+(NSOperationQueue*)sharedOperationQueue;
@end

// NSOperationQueue+SharedQueue.m
@implementation NSOperationQueue (SharedQueue)
+(NSOperationQueue*)sharedOperationQueue;
{
  static NSOperationQueue* sharedQueue = nil;
  if (sharedQueue == nil) {
    sharedQueue = [[NSOperationQueue alloc] init];
  }
  return sharedQueue;
}
@end

This way I do not need to manage a whole bunch of queues unless I really need to. I have easy access to a shared queue from all my view controllers.

I have even added a category to NSObject to make it even easier to add new operations on this shared queue:

// NSObject+SharedQueue.h
@interface NSObject (SharedQueue)
-(void)performSelectorOnBackgroundQueue:(SEL)aSelector withObject:(id)anObject;
@end

// NSObject+SharedQueue.m
@implementation NSObject (SharedQueue)
-(void)performSelectorOnBackgroundQueue:(SEL)aSelector withObject:(id)anObject;
{
  NSOperation* operation = [[NSInvocationOperation alloc] initWithTarget:self
                                                                selector:aSelector
                                                                  object:anObject];
  [[NSOperationQueue sharedOperationQueue] addOperation:operation];
  [operation release];
}
@end

Answer 3

If you already have a pointer to a class that handles connections in each view/view controller, there's no reason you would also need to have a pointer to the operation queue.

I suppose what you want to do is something like: a) view(Controller) hands url(+data) to server handling object, b) server handling objects creates operation and puts it in a queue that it and only it has a pointer to.

It's hard to figure out why that didn't work if you don't provide more detail.

I highly recommend taking a look at ASIHTTPRequest which provides a NetworkQueue class to handle this kind of task. It has several convenient delegate fields that lets you register to keep track of progress, know when a download or upload finished etc.