我一直在寻找从远程服务器图像 URL 异步加载图像的良好解决方案。网上有很多解决方案。遗憾的是,Apple 没有为如此常见的东西提供原生服务。不管怎样,我找到了Sundell's blog真的很有趣,并从中汲取了一些好处,创建了我自己的 ImageLoader,如下所示:
import Combine
class ImageLoader {
private let urlSession: URLSession
private let cache: NSCache<NSURL, UIImage>
init(urlSession: URLSession = .shared,
cache: NSCache<NSURL, UIImage> = .init()) {
self.urlSession = urlSession
self.cache = cache
}
func publisher(for url: URL) -> AnyPublisher<UIImage, Error> {
if let image = cache.object(forKey: url as NSURL) {
return Just(image)
.setFailureType(to: Error.self)
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
} else {
return urlSession
.dataTaskPublisher(for: url)
.map(\.data)
.tryMap { data in
guard let image = UIImage(data: data) else {
throw URLError(.badServerResponse, userInfo: [
NSURLErrorFailingURLErrorKey: url
])
}
return image
}
.receive(on: DispatchQueue.main)
.handleEvents(receiveOutput: { [cache] image in
cache.setObject(image, forKey: url as NSURL)
})
.eraseToAnyPublisher()
}
}
}
如您所见,发布者提供了 AnyPublisher<UIImage, Error>
的实例.我不完全确定如何使用这个 ImageLoader
在我的MyImageView
如下图:
struct MyImageView: View {
var url: URL
var imageLoader = ImageLoader()
@State private var image = #imageLiteral(resourceName: "placeholder")
var body: some View {
Image(uiImage: image)
.onAppear {
let cancellable = imageLoader.publisher(for: url).sink(receiveCompletion: { failure in
print(failure) // doesn't print
}, receiveValue: { image in
self.image = image // not getting executed
})
cancellable.cancel() // tried with and without this line.
}
}
}
如何提取 UIImage
来自 ImageLoader
返回 AnyPublisher<UIImage, Error>
实例的发布者?
最佳答案
您必须使用 ObservableObject
来订阅 ImageLoader 提供的发布者。
class ImageProvider: ObservableObject {
@Published var image = UIImage(named: "icHamburger")!
private var cancellable: AnyCancellable?
private let imageLoader = ImageLoader()
func loadImage(url: URL) {
self.cancellable = imageLoader.publisher(for: url)
.sink(receiveCompletion: { failure in
print(failure)
}, receiveValue: { image in
self.image = image
})
}
}
struct MyImageView: View {
var url: URL
@StateObject var viewModel = ImageProvider()
var body: some View {
Image(uiImage: viewModel.image)
.onAppear {
viewModel.loadImage(url: url)
}
}
}
关于swift - 使用 combine's Publisher 在 SwiftUI Image 中从远程 URL 异步加载图像,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/64854765/