SwiftUI:后台线程结束后更新UI

struct ContentView: View {
    @State var image: UIImage?
    
    var body: some View {
        VStack {
            if let image = image {
                Image(uiImage: image)
                    .resizable()
                    .aspectRatio(contentMode: .fit)
            } else {
                Text("Downloading image...")
            }
        }
        .onAppear {
            // 启动后台线程下载图片
            DispatchQueue.global().async {
                // 模拟耗时操作
                Thread.sleep(forTimeInterval: 2)
                
                // 下载图片
                let imageURL = URL(string: "https://example.com/image.jpg")!
                if let data = try? Data(contentsOf: imageURL) {
                    self.image = UIImage(data: data)
                }
            }
        }
    }
}