如何在调用Task.cancel()时检测URLSession取消请求

Question

大家！我想在 1 秒后取消加载图像，或者通过用户操作（例如）取消加载图像并显示加载的图像。

这就是我所做的：

enum DownloadError: Error {
    case invalidStatusCode
    case badImage
    case unknown
}

func downloadImageWithImageId(imageId: Int) async throws -> UIImage {
    let imageUrl = URL(string: "https://github.com/yavuzceliker/sample-images/blob/main/images/image-\(imageId).jpg?raw=true")!
    let imageRequest = URLRequest(url: imageUrl)
    let (data, response) = try await URLSession.shared.data(for: imageRequest)
    if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode != 200 {
        throw DownloadError.invalidStatusCode
    }

    guard let image = UIImage(data: data) else {
        throw DownloadError.badImage
    }
    return image
}

func reloadImages() {
    imageShowingTask = Task {
        images = []
        await view?.reloadImages()

        do {
            await view?.showSpinner(isLoading: true)

            var imagesLoaded = [UIImage]()

            for i in 1...5 {
                async let image = try downloadImageWithImageId(imageId: i)

                if Task.isCancelled {
                    print("---CANCELLED")
                    break
                }

                try await imagesLoaded.append(image)
            }

            self.images = imagesLoaded
            await view?.showSpinner(isLoading: false)
            await view?.reloadImages()
        } catch (let error) {
            print(error.localizedDescription) // here I want to detect error by URLSession
        }
    }

    Task {
        sleep(1)
        imageShowingTask?.cancel()
    }
}

但是我没有得到“---取消”打印，而是在

catch

块中得到了“取消”打印。 所以取消是不行的。预先感谢！

Answer 1

您应该捕获取消任务时抛出的 CancelationError，而不是检查 isCancelled

} catch is CancellationError {
    print("---CANCELLED")
}