Wsrtjtyk

I am building an app that has several images(Plans) that are loaded and setup on a scrollview with a page content. I am trying to load the first image on the main thread and then load the surrounding images from it's index on a background thread. All the UIImageViews are in an array (planImages) to reference when I need to set their images with the loaded data.

The problem is the images aren't always updating with the recently loaded images. This is my first time using Dispatch, so is there something I am doing wrong? Here is the section of code that is giving me the issue.

    func setupPagesInScrollView(firstImage: Int)

{

    let numberOfPages: CGFloat = CGFloat(selectedDetails!.numberOfPlans)



    scrollView!.contentSize = CGSize(width: scrollView!.frame.width * numberOfPages, height: scrollView!.frame.height)

    pageControl!.numberOfPages = selectedDetails!.numberOfPlans



    if(planImages.count < selectedDetails!.numberOfPlans)

    {

        for index in planImages.count...selectedDetails!.numberOfPlans - 1

        {

            let iView = UIImageView()

            iView.frame = CGRect(x: 0, y: 0, width: scrollView!.frame.width, height: scrollView!.frame.height)

            planImages.append(iView)

            scrollView!.addSubview(iView)



            iView.translatesAutoresizingMaskIntoConstraints = false

            iView.topAnchor.constraint(equalTo: scrollView!.topAnchor).isActive = true

            iView.leftAnchor.constraint(equalTo: scrollView!.leftAnchor, constant: scrollView!.frame.width * CGFloat(index)).isActive = true

            iView.heightAnchor.constraint(equalToConstant: scrollView!.contentSize.height).isActive = true

            iView.widthAnchor.constraint(equalToConstant: scrollView!.frame.width).isActive = true

        }

    }



    DispatchQueue.global(qos: .background).async

        {

            //Load first selected image

            let path = self.selectedDetails!.dirPath + self.selectedDetails!.plansName

            self.setupImageAtIndex(path: path, index: firstImage)



            //Build Image data around first image on background threads

            var mask = 1

            let max = self.selectedDetails!.numberOfPlans



            while firstImage + mask < max || firstImage - mask > 0

            {

                if(firstImage + mask < max)

                {

                    self.setupImageAtIndex(path: path, index: firstImage + mask)

                }



                if(firstImage - mask >= 0)

                {

                    self.setupImageAtIndex(path: path, index: firstImage - mask)

                }



                mask = mask + 1

            }



            //Remove extra images from memory if needed

            if(self.planImages.count > self.selectedDetails!.numberOfPlans)

            {

                let dif = self.planImages.count - self.selectedDetails!.numberOfPlans



                for _ in 1...dif

                {

                    let index = self.planImages.count - 1

                    let plan = self.planImages[index]

                    self.planImages.remove(at: index)

                    plan.removeFromSuperview()

                    plan.image = nil

                }

            }

    }

}



private func setupImageAtIndex(path: String, index: Int)

{

    let imageName = index + 1 > 9 ? path + String(index + 1) : path + "0" + String(index + 1)



    planImages[index].image = UIImage(contentsOfFile: imageName)

}

As per apple documentation You must update UI elements on the main queue.

Update your code like this

private func setupImageAtIndex(path: String, index: Int)

    {

        let imageName = index + 1 > 9 ? path + String(index + 1) : path + "0" + String(index + 1)

        DispatchQueue.main.async {

            planImages[index].image = UIImage(contentsOfFile: imageName)



        }

    }