缩小但不放大 SwiftUI 图像 [英] Downsize but not upsize a SwiftUI image

问题描述

我有一个个人资料图片(各种尺寸)的列表，我希望每个图片都缩小以适应其视图，但我不希望它们被放大和像素化.相反，我希望小图像保持它们的分辨率.我怎样才能做到这一点?

I have a list of profile images (of various sizes) that I want each one to downsize to fit into its view, but I don't want them to be upsized and be pixilated. Instead, I want small images to stay at the resolution they are at. How do I can achieve this?

这是我到目前为止一直在使用的(但它调整了大小):

This is what I've been using so far (but it resizes up):

VStack {        
    Image(...)
         .resizable()
         .scaledToFill()
}.frame(width:200, height:200)

推荐答案

我也没有在 API 中找到简单的解决方案，所以这里有一个看起来适合我的占位符.作品有点复杂.

I did not find simple solution in API either, so here is a placeholder that looks appropriate for me. It is a bit complicated by works.

使用 Xcode 11.2+/iOS 13.2+ 测试.

Tested with Xcode 11.2+ / iOS 13.2+.

使用演示:

struct DemoImagePlaceholder_Previews: PreviewProvider {
    static var previews: some View {
        VStack {
            ImagePlaceholder(image: Image("icon"), size: CGSize(width: 200, height: 200))
                .border(Color.red)
            ImagePlaceholder(image: Image("large_image"), size: CGSize(width: 200, height: 200))
                .border(Color.red)
        }
    }
}

解决方案:

struct OriginalImageRect {
    var rect: Anchor<CGRect>? = nil
}

struct OriginalImageRectKey: PreferenceKey {
    static var defaultValue: OriginalImageRect = OriginalImageRect()

    static func reduce(value: inout OriginalImageRect, nextValue: () -> OriginalImageRect) {
        value = nextValue()
    }
}

struct ImagePlaceholder: View {
    let image: Image
    let size: CGSize

    var body: some View {
        VStack {
            self.image.opacity(0)
                .anchorPreference(key: OriginalImageRectKey.self, value: .bounds) {
                    OriginalImageRect(rect: $0)
                }
        }
        .frame(width: size.width, height: size.height)
        .overlayPreferenceValue(OriginalImageRectKey.self) { pref in
            GeometryReader { gp -> Image in
                if pref.rect != nil, CGRect(origin: .zero, size: gp.size).contains(gp[pref.rect!]) {
                    return self.image
                } else {
                    return self.image.resizable() // .fill by default, otherwise needs to wrap in AnyView
                }
            }
        }
    }
}

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