SwiftUI 错误：无法将类型为"UIImage？"的值转换为闭包结果类型"Void"

Question

我得到以下SwiftUI错误：

var assetImage : UIImage? {
if PHPhotoLibrary.authorizationStatus() == .authorized {
let allPhotosOptions = PHFetchOptions()
allPhotosOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let assetsFetchResults = PHAsset.fetchAssets(with: allPhotosOptions)
if assetsFetchResults.count > 0 {
let asset = assetsFetchResults.lastObject
if asset != nil {
let options = PHImageRequestOptions()
options.isNetworkAccessAllowed = true
options.version = .current

PHCachingImageManager().requestImage(for: asset!, targetSize: CGSize(width: 64 * UIScreen.main.scale, height: 64 * UIScreen.main.scale), contentMode: .aspectFill, options: options, resultHandler: { img, _ in
DispatchQueue.main.async {
return img //Error Here
}
})
} else {
return nil
}
} else {
return nil
}
}
return nil
}

我得到以下错误：

Cannot convert value of type 'UIImage?' to closure result type 'Void'

Answer 1

在从PHCachingImageManager异步访问图像时，将其更改为具有completionHandler的方法，而不是计算属性。

func assetImage(_ completion: @escaping (UIImage?) -> Void) {
if PHPhotoLibrary.authorizationStatus() == .authorized {
let allPhotosOptions = PHFetchOptions()
allPhotosOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let assetsFetchResults = PHAsset.fetchAssets(with: allPhotosOptions)
if assetsFetchResults.count > 0 {
let asset = assetsFetchResults.lastObject
if asset != nil {
let options = PHImageRequestOptions()
options.isNetworkAccessAllowed = true
options.version = .current

PHCachingImageManager().requestImage(for: asset!, targetSize: CGSize(width: 64 * UIScreen.main.scale, height: 64 * UIScreen.main.scale), contentMode: .aspectFill, options: options, resultHandler: { img, _ in
DispatchQueue.main.async {
completion(img)
}
})
} else {
completion(nil)
}
} else {
completion(nil)
}
} else {
completion(nil)
}
}

用法

self.assetImage { (image) in

}