Question

I m calling a NSOperation from a Subview of a NavigationController.

MyOperation *op = [[MyOperation alloc] target:self action:@selector(didFinishOperation)];

The Operation loads some data from a server, parses it and then sends a

[target performSelectorOnMainThread:action withObject:nil waitUntilDone:YES];

when the job is done. This is generally working...

The problem is when I push the back button from the navigation controller while the NSOperation is doing its job, the app crashes because the action references a deallocated instance.

I ve tried retaining the operation - but it still crashes...

Thanks in advance

Answer 1

Chris is on the right track, but it doesn t cover the case where the operation completes as you try to cancel it, and it will still crash. If the operation is executing in main, the cancel won t take effect.

Still, try and cancel it before your target is destroyed, but test that the target still exists before attempting to send it a message. Also, check if you re cancelled before trying to send the message:

if ( self.isCancelled ) return;

Answer 2

In your UIView dealloc method, you could cancel the operation and remove it from its NSOperationQueue.

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