How to pass value to completion handler in Swift?

Question

I would like to pass a integer to a completion handler. Because the handler is asynchronous the value of count might be inaccurate by the time the completion handler gets a chance to run? I would like to pass the CURRENT value of count to the handler so that count is accurate when the handler is called. How do I do this?

// Take image
    func didPressTakePhoto(){

        if let videoConnection = stillImageOutput?.connection(withMediaType: AVMediaTypeVideo){

            videoConnection.videoOrientation = AVCaptureVideoOrientation.portrait

            count = count + 1

            //Capture image.  everything in this closure is ASYNCHRONOUS?
            stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: {
                (sampleBuffer, error) in

                //Do something with count...

            })
        }
    }

Answer 1

Since you have no declaration in this function for count , I will assume that count is a parameter. If so, then accessing count using self.count (mandatory in a block) will get the latest value of count , even if it changes after you call captureStillImageAsynchronously() .

If there is any chance that count can be written and read at the same time by multiple sources, you should ensure it is thread safe.