CODEWITHSUNDEEP
objective-cnsoperationnsoperationqueue
Jonathan
Jonathan

Reputation: 1602

NSOperation best practice, responding to cancellation

In my NSOperation subclasses i check for cancellation at top of lengthly loops or before any lengthly methods (Core Data Fetches, Array Sorting etc.) in the subclass's main method. See an example below.

-(void)main{

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    for( int i=0; i< 100; i++ )
    {
         //Check for cancellation
         if( [self isCancelled] ){
             [pool drain];
             return;
         }

    //Do the work
    }

    [pool drain];
}

Is there anything else i ought to be doing, apart from draining the pool, and exiting the method as fast as possible?

Upvotes: 1

Views: 742

Answers (1)

justin
justin

Reputation: 104708

1) exit gracefully

2) inform listeners/delegates appropriately. if you have a delegate, you'll want to provide callbacks or interfaces/protocols which support multiple operation results (success, fail or error, cancel, timeout). your listeners will not necessarily be the object which called cancel, but they may have a better idea how to handle such a situation.

3) cleanup your object's state - e.g., release and zero objects which should be programmatically inaccessible, and make sure that any invocation will check isCancelled if the operation operates in a multithreaded context.

Upvotes: 2

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