计算UIScrollView的内容大小

Question

 func setupScrollView(){
        let scrollWidth = scrollView.frame.size.width
        let scrollHeight = scrollView.frame.size.height

        scrollView.isPagingEnabled = true

        var contentWidth : CGFloat = 0.0

        for x in 0...bannerImages.count - 1 {

            let image = (UIImage(named: bannerImages[x]))
            let imageView = UIImageView(image: image)
            imageView.clipsToBounds = true

            var newX : CGFloat = 0.0
            newX = scrollWidth / 2 + scrollWidth * CGFloat(x)
            contentWidth += newX
            scrollView.addSubview(imageView)
            imageView.frame = CGRect(x: newX - itemWidth / 2, y: scrollView.frame.midY - itemWidth / 2, width: itemWidth, height: itemWidth)

        }

        scrollView.contentSize = CGSize(width:contentWidth, height: scrollHeight)

    }

I've got this in my viewDidAppear and I have no autolayout in play.

My content size width is adding a ton of space that shouldn't be there. I've got 3 images I'm showing and I can scroll past the 3rd image with paging 2 more times.

Any ideas?

Answer 1

I am not sure what you are trying to accomplish but I think your math is off. If you are trying to stack three images on the x axes in a scrollview and set the scrollview content size to the sum of your image widths then calculate your newX like this newX = itemWidth * CGFloat(x) also set image frame like this imageView.frame = CGRect(x: newX, y: scrollView.frame.midY - itemWidth / 2, width: itemWidth, height: itemWidth) .

I don't think this is a right way of implementing ScrollView ! Probably not a best practice. I think you should have a child view in your ScrollView call it contentView and then set appropriate AutoLayout Constraints for that view. After that add each image to contentView . That way things would be easier.

Check out this blog post https://www.natashatherobot.com/ios-autolayout-scrollview/

Answer 2

I Update this code check comments....

    func setupScrollView(){
        let scrollWidth = scrollView.frame.size.width
        let scrollHeight = scrollView.frame.size.height

        scrollView.isPagingEnabled = true

        var contentWidth : CGFloat = 0.0

        for x in 0...bannerImages.count - 1 {

            let imageView = UIImageView(image: bannerImages[x])
            imageView.clipsToBounds = true

            var newX : CGFloat = 0.0
            newX = scrollWidth / 2 + scrollWidth * CGFloat(x)
//            contentWidth += newX
            // This is wrong here. Because you already add scrollview widht in newx and by this line you are adding it again.
            contentWidth = newX
            scrollView.addSubview(imageView)
            imageView.frame = CGRect(x: newX - itemWidth / 2, y: scrollView.frame.midY - itemWidth / 2, width: itemWidth, height: itemWidth)

        }
        contentWidth = contentWidth + (itemWidth / 2)
        // Add this line also beacuse newx store half width so you have to add extra half space in content width
        scrollView.contentSize = CGSize(width:contentWidth, height: scrollHeight)

    }