[在SwiftUI应用中使用PHCachingImageManager显示PHAsset（照片）-主体视图中的IF语句不起作用

Question

我正在尝试在我的SwiftUI应用中使用PHCachingImageManager加载照片。我可以获取照片，但无法获取SwiftUI视图来显示它。

我有一个称为PhotoCell的视图，如下所示。我将Binding<UIImage>传递给使用PHCachingImageManager加载资产的函数。这可以起作用，并将90x120的图像返回到Binding的设置功能。在设置功能内，您可以看到hasLoadedImage设置为true。

视图的body由if语句组成。除了第一次hasLoadedImage的值为false时，都不会执行此操作。我不知道该怎么办。正如测试一样，我将Image内的if替换为Text，但即使hasLoadedImage设置为true，它也不会显示。我在if getter中经常使用body语句。

我觉得我已经忽略了显而易见的事情。

struct PhotoCell: View {

    @State var photoImage: UIImage = UIImage()
    @State var hasLoadedImage: Bool = false

    var photoAsset: PHAsset

    var photoBinding: Binding<UIImage> {
        Binding<UIImage>(
            get: {
                return self.photoImage
        },
            set: {(newValue) in
                print("Loaded image \(newValue.size)") // this prints with the correct size
                self.photoImage = newValue
                self.hasLoadedImage = true // seems to have no effect
        })
    }

    init(photoAsset: PHAsset) {
        self.photoAsset = photoAsset

        let options: PHImageRequestOptions = PHImageRequestOptions()
        options.deliveryMode = .fastFormat
        options.isNetworkAccessAllowed = true
        options.resizeMode = .fast

        PhotosManager.shared.loadAsset(asset: photoAsset, size: CGSize(width: 48, height: 48), options: options, image: self.photoBinding)
    }

    var body: some View {
        if self.hasLoadedImage { // shouldn't this execute once the value is changed??
            return AnyView(
                Image(uiImage: self.photoImage)
                    .resizable()
                    .frame(width: 48, height: 48)
            )
        } else {
            return AnyView(
                Image(systemName: "goforward")
            )
        }
    }
}

Answer 1

因此，出于无​​奈，我想出了一种解决方法，它实际上比我想做的要简单。我为UIViewRepresentable构建了UIImageView包装器：

struct MyImage: UIViewRepresentable {

    var photoAsset: PHAsset

    func makeUIView(context: Context) -> UIImageView {
        let uiView = UIImageView(image: UIImage(systemName: "goforward") ?? UIImage())
        return uiView
    }

    func updateUIView(_ uiView: UIImageView, context: Context) {
        let options: PHImageRequestOptions = PHImageRequestOptions()
        options.deliveryMode = .fastFormat
        options.isNetworkAccessAllowed = true
        options.resizeMode = .fast

        PhotosManager.shared.loadAsset(asset: photoAsset, into: uiView, options: options)
    }
}

loadAsset函数就是这样，如果要对其进行测试，其中imageManager是PHCachingImageManager的实例。我想了解为什么我发布的问题不起作用。我怀疑这与requestImage中的闭包和不当捕获self有关，但我只是看不到它。

func loadAsset(asset: PHAsset, into imageView: UIImageView, options: PHImageRequestOptions?) {
        let size = CGSize(width: 48, height: 48)
        imageManager.requestImage(for: asset, targetSize: size, contentMode: .aspectFit, options: options, resultHandler: { (result, info) in
            if let result = result {
                imageView.image = result
            }
        })
    }