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c# - 取消 Windows 10 BackgroundDownloader

转载 作者:行者123 更新时间:2023-11-30 14:25:42 24 4
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我想为 BackgroundDownloader 实现超时功能。当我超时时,我无法取消下载操作。所以我这样使用它:

   public async void downloadFile(string fileUrl, string fileName) {
var myFolder = await StorageFolder.GetFolderFromPathAsync(Package.Current.InstalledLocation.Path);
var myFile = await myFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

var downloader = new BackgroundDownloader();
var downloadOperation = downloader.CreateDownload(new Uri(fileUrl), myFile);

var task = Task.Run(async () => await downloadOperation.StartAsync().AsTask());
if ( task.Wait(TimeSpan.FromMilliseconds(1000)) ) {
// file is downloaded in time

} else {
// timeout is reached - how to cancel downloadOperation ?????

}
}

我在尝试:

downloadOperation.StartAsync().Cancel();

我明白了

WinRT information: This operation was already started. Call AttachAsync to attach to a running download/upload.

downloadOperation.AttachAsync().Cancel();

我明白了

Exception thrown: 'System.Runtime.InteropServices.COMException' in Project.exe WinRT information: This operation was not started. Call StartAsync to start the operation.Additional information: A method was called at an unexpected time.

我们将不胜感激任何想法!

最佳答案

When I reach timeout i can't cancel download operation. I was trying : downloadOperation.AttachAsync().Cancel();

根据我的测试,downloadOperation.AttachAsync().Cancel(); 在我的网站上运行良好。以下是我用于测试的代码:

public async void downloadFile(string fileUrl, string fileName)
{
var myFolder = await StorageFolder.GetFolderFromPathAsync(Package.Current.InstalledLocation.Path);
var myFile = await myFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

var downloader = new BackgroundDownloader();
var downloadOperation = downloader.CreateDownload(new Uri(fileUrl), myFile);

var task = Task.Run(async () => await downloadOperation.StartAsync().AsTask());
if (task.Wait(TimeSpan.FromMilliseconds(1000)))
{
// file is downloaded in time
}
else {
// timeout is reached - how to cancel downloadOperation ?????
downloadOperation.AttachAsync().Cancel();
}
}

通常我们使用CancellationToken取消下载操作。此外,使用 Task.Wait方法将阻塞 UI 线程,这会导致糟糕的用户体验。所以使用 CancellationTokenSource.CancelAfter方法在您的场景中可能是更好的选择。

以下是我验证过的代码:

public async void downloadFile(string fileUrl, string fileName)
{
var myFolder = await StorageFolder.GetFolderFromPathAsync(Package.Current.InstalledLocation.Path);
var myFile = await myFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

var downloader = new BackgroundDownloader();
var downloadOperation = downloader.CreateDownload(new Uri(fileUrl), myFile);

// Define the cancellation token.
CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;

cts.CancelAfter(1000);
try
{
// Pass the token to the task that listens for cancellation.
await downloadOperation.StartAsync().AsTask(token);
// file is downloaded in time
}
catch (TaskCanceledException)
{
// timeout is reached, downloadOperation is cancled
}
finally
{
// Releases all resources of cts
cts.Dispose();
}
}

关于c# - 取消 Windows 10 BackgroundDownloader,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/37548454/

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