How do I setup a completion block in this scenario?

Question

I have a function that has a problem in it. The following line seems to require a delay in order to accurately process whatever data it's processing, but it's not getting that time and and as a result I'm getting the wrong result. The following line:

self.failure = failure

Seems to need about 5-7 seconds to execute, but the problem is that the next line of code is executed before it can finish.

I need to setup self.failure = failure in a way where the rest of the code in the function executes inside a completion block once that line has finished. I'm just not sure how to do it.

I've tried creating a typedef for a completion block, but I have no idea how and where to execute it.

- (void)start:(BMPlaybackStartupProcessCompleteBlock)completion
      failure:(BMPlaybackStartupProcessFailureBlock)failure // what is the error code at the start and end of this method?
    {
        NSParameterAssert(completion);
        NSParameterAssert(failure);

        self.completion = completion;
        self.failure = failure;

        NSOperation *jailBreakOperation = [self jailBreakCheckOperation];
        NSOperation *metadata = [self metadataOperation];
        NSOperation *ads = [self adsOperation];
        NSOperation *mediaPlayer = [self mediaPlayerOperation];
        NSOperation *progress = [self progressTrackerOperation];
        NSOperation *final = [self finalOperation];

        [final addDependency:mediaPlayer];
        [final addDependency:progress];
        if (ads)
        {
            [final addDependency:ads];
            [ads addDependency:metadata];
        }
        [mediaPlayer addDependency:metadata];
        [progress addDependency:metadata];
        [metadata addDependency:jailBreakOperation];

        [self.queue addOperation:final];
        if (ads)
        {
            [self.queue addOperation:ads];
        }
        [self.queue addOperation:mediaPlayer];
        [self.queue addOperation:progress];
        [self.queue addOperation:metadata];
        [self.queue addOperation:jailBreakOperation];

                // INPUTS:
        //  - content ID
        //  - metadata component
        //  - media player component
        //  - ads component
        //  - location manager if required
        //  - auto play?

        // OUTPUTS:
        //  - Possibly an error if not successful
        //  - metadata
        //  - playback details
}

I want self.failure = failure to finish BEFORE the NSOperationQueue stuff executes.

You would need to actually call the block. Now you're assigning it to a property, I don't believe that that takes more that a part of a split second. Calling the function would look like failure(); but I'm a bit confused of why you'd want to call the fail block before you did a thing. — Julian F. Weinert
I guess that one of the first operations takes a long time. You'd want to call the block in case of a failure or the successblock after everything is done. But keep in mind that your operations won't run asynchroniously, but hard to say what the rest of your code does. — Julian F. Weinert

DevesH DevesH · Accepted Answer · 2019-11-14T14:13:15

NSOperation has completionBlock property.

@property(copy) void (^completionBlock)(void);

So you can perform your operation like this. This will handle failure if occured.

    Create `error` block level property to save error while operation. 

    nsOperatorObject.completionBlock(^{
        if (self.error) {
          self.failure();
        } else {
          self.completion();
        }
    });

This might be wrong answer . Sorry for that :)

How do I setup a completion block in this scenario?

1 Answers