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 connections, should I try to create a global NSOperationQueue in the app delegate, or should I have one in each of the views? I’m not familiar with NSOperationQueue.

I’d like to know a) what the best practice is and b) if there is no best practice, what the tradeoffs are if any.

I did try to put the operation queue in the class (as a property) where I handle the server connections but the task never fired. Couldnt figure it out but [queue operations] = 0. If someone knows a solution to this, I presume this would be the best place to put it.

Answer 1

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