Question

In my app, I use operations to perform time-intensive tasks, so my user interface won’t freeze. For that, I use NSInvocationOperation. I wanted to test the overall architecture first before implementing the code to actually complete the tasks, so that’s what I have right now:

// give the object data to process
- (void)processData:(NSObject*)dataToDoTask {

    ... // I store the data in this object

    NSInvocationOperation *newOperation =
    [[NSInvocationOperation alloc] initWithTarget:self
                                         selector:@selector(performTask)
                                           object:nil];

    [[NSOperationQueue mainQueue] addOperation:newOperation];

    ...

}

// process data stored in the object and return result
- (NSObject*)performTask {

    [NSThread sleepForTimeInterval:1]; // to emulate the delay
    return [NSString stringWithFormat:@"unimplemented hash for file %@", self.path];
}

However, the sleep doesn’t work as I expect: instead of delaying the operation completetion, it freezes the app. It seems that I either operations or sleep incorrectly, but I can’t figure out which and how.

Answer 1

That is because you are running your operation on the main thread (the same running your user interface).

If you want to run your operation concurrently, create a new operation queue:

NSOperationQueue * queue = [NSOperationQueue new];
[queue addOperation:newOperation];