Should I create one NSOperationQueue per UIViewController?

Question

In almost every UIViewController I have a bunch of AFHTTPRequestOperations and I have to properly handle any kind of cancel (pressing cancel button, going back in UINavigationController's stack, etc.). I was wondering if creating one NSOperationQueue per each UIViewController and adding to it all operations called within controller would be a proper way to go? I was aiming for cancelling all operations [[NSOperationQueue mainQueue] cancelAllOperations] but this will kill all operations already started, especially those called from previous UIViewController. Or should I create property for each operation, call it in viewWillDissappear:(BOOL)animated and set if statement for cancel state in success block?

Answer 1

AFHTTPRequestOperationManager instances are cheap to create and each has its own operation queue, so it is easy to cancel all of a given UIViewController's operations:

- (void)dealloc {
    [self.requestOperationManager.operationQueue cancelAllOperations];
}

This will cancel any request created through self.requestOperationManager. You can create the AFHTTPRequestOperationManager in your UIViewController's init method.

I recommend cancelling operations in your view controller's dealloc method, as you know it will no longer be needed.

Answer 2

Tried David Caunt answer, but didn't work for me. dealloc wasn't called when I pushed back button, so I guess the best way to cancel operations is to call it in viewWillDisappear: (my bad was to use && not || - silly mistake, but easiest things are often hardest to find)

- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated]; 
if (self.isMovingFromParentViewController && self.isBeingDismissed){
    DDLogDebug(@"back or dismissed!"); 
    [self.manager.operationQueue cancelAllOperations]; } 
}