xcode UIScrollView 缩放 & contentInset

UIScrollView Zooming & contentInset

提问by Gizmodo

Simliar to iOS Photos App where the user is zooming in and out of an image by pinching:

类似于用户通过捏合来放大和缩小图像的 iOS 照片应用程序：

UIView > UIScrollView > UIImageView > UIImage

UIView > UIScrollView > UIImageView > UIImage

Initially, I had the issue of zooming below scale 1: image being off centered. I got it fixed by doing this:

最初，我遇到了缩放比例低于 1 的问题：图像偏离中心。我通过这样做修复了它：

func scrollViewDidZoom(scrollView: UIScrollView) {
        let offsetX = max((scrollView.bounds.width - scrollView.contentSize.width) * 0.5, 0)
        let offsetY = max((scrollView.bounds.height - scrollView.contentSize.height) * 0.5, 0)
        scrollView.contentInset = UIEdgeInsetsMake(offsetY, offsetX, 0, 0)
}

This works well when zooming out.

这在缩小时效果很好。

UIImage content mode is aspectFit

UIImage 内容模式是 aspectFit

Issue

问题

When I ZOOM IN, when zoomScale is above 1, scroll view insets need to hug the surroundings of the UIImage that the scroll view contains. This takes away the dead-space that was surrounding the UIImage. IE, Photos app when zooming-in by pinching or double tapping.

当我放大时，当 zoomScale 大于 1 时，滚动视图插图需要拥抱滚动视图包含的 UIImage 的周围环境。这消除了 UIImage 周围的死空间。通过捏合或双击放大时的 IE、照片应用程序。

Tried

试过

    func scrollViewDidZoom(scrollView: UIScrollView) {
    if scrollView.zoomScale > 1 {
        let imageScale = (self.imageView.bounds.width/self.imageView.image!.size.width)
        let imageWidth = self.imageView.image!.size.width * imageScale
        let imageHeight = self.imageView.image!.size.height * imageScale
        scrollView.contentInset = UIEdgeInsetsMake(((scrollView.frame.height - imageHeight) * 0.5), (scrollView.frame.width - imageWidth) * 0.5 , 0, 0)
        print (scrollView.contentInset.top)
    }
    else {

        let offsetX = max((scrollView.bounds.width - scrollView.contentSize.width) * 0.5, 0)
        let offsetY = max((scrollView.bounds.height - scrollView.contentSize.height) * 0.5, 0)
        scrollView.contentInset = UIEdgeInsetsMake(offsetY, offsetX, 0, 0)
    }
}

Above addition seems to vary the inset amount still.

以上添加似乎仍然改变插入量。

Update (images added)

更新（已添加图片）

First image shows the default layout. Rest shows when zoomed in.....

第一张图片显示了默认布局。放大时休息显示.....

回答by Arun Ammannaya

Your approach looks correct. You need to update your code as below.

你的方法看起来是正确的。您需要更新您的代码，如下所示。

    func scrollViewDidZoom(scrollView: UIScrollView) {

    if scrollView.zoomScale > 1 {

        if let image = imageView.image {

            let ratioW = imageView.frame.width / image.size.width
            let ratioH = imageView.frame.height / image.size.height

            let ratio = ratioW < ratioH ? ratioW:ratioH

            let newWidth = image.size.width*ratio
            let newHeight = image.size.height*ratio

            let left = 0.5 * (newWidth * scrollView.zoomScale > imageView.frame.width ? (newWidth - imageView.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
            let top = 0.5 * (newHeight * scrollView.zoomScale > imageView.frame.height ? (newHeight - imageView.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))

            scrollView.contentInset = UIEdgeInsetsMake(top, left, top, left)
        }
    } else {
        scrollView.contentInset = UIEdgeInsetsZero
    }
}

回答by Jo?o Rocha

Swift 5

斯威夫特 5

func scrollViewDidZoom(_ scrollView: UIScrollView) {
    if scrollView.zoomScale > 1 {
        if let image = imageView.image {

            let ratioW = imageView.frame.width / image.size.width
            let ratioH = imageView.frame.height / image.size.height

            let ratio = ratioW < ratioH ? ratioW : ratioH

            let newWidth = image.size.width * ratio
            let newHeight = image.size.height * ratio

            let left = 0.5 * (newWidth * scrollView.zoomScale > imageView.frame.width ? (newWidth - imageView.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
            let top = 0.5 * (newHeight * scrollView.zoomScale > imageView.frame.height ? (newHeight - imageView.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))

            scrollView.contentInset = UIEdgeInsets(top: top, left: left, bottom: top, right: left)
        }
    } else {
        scrollView.contentInset = UIEdgeInsets.zero
    }
}

回答by Ansal Antony

for swift 4

快速 4

func scrollViewDidZoom(_ scrollView: UIScrollView) {

        if scrollView.zoomScale > 1 {

            if let image = self.imageViewZoom.image {

                let ratioW = self.imageViewZoom.frame.width / image.size.width
                let ratioH = self.imageViewZoom.frame.height / image.size.height

                let ratio = ratioW < ratioH ? ratioW:ratioH

                let newWidth = image.size.width*ratio
                let newHeight = image.size.height*ratio

                let left = 0.5 * (newWidth * scrollView.zoomScale > self.imageViewZoom.frame.width ? (newWidth - self.imageViewZoom.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
                let top = 0.5 * (newHeight * scrollView.zoomScale > self.imageViewZoom.frame.height ? (newHeight - self.imageViewZoom.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))

                scrollView.contentInset = UIEdgeInsetsMake(top, left, top, left)
            }
        } else {
            scrollView.contentInset = UIEdgeInsets.zero
        }
    }