在C＃的Google驅動器中下載時無法更新進度欄

Question

我正在使用Google Drive V3 API。 下載文件時我嘗試更新進度，但似乎無法正常工作。

我使用Dispatcher.BeginInvoke（）更新了progressbar的值。

當我在progressBar.Value上調試時，它沒有跳到這一行： progressBar.Value = Convert.ToDouble（progress.BytesDownloaded * 100 / fileSize）;

我已經在Google和stackoverflow中進行搜索，但找不到解決方案。

請幫忙。 謝謝高級！

MainWindow.xaml

<Window x:Class="DownloadProgress.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:DownloadProgress"
        mc:Ignorable="d"
        Title="MainWindow" Height="150" Width="400">
    <StackPanel>
        <ProgressBar Height="30" Margin="10" Name="progressBar"/>
        <Button Height="30" Content="Downloads" Margin="10" Click="StartDownload"/>
    </StackPanel>
</Window>

MainWindow.xaml.cs

public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void StartDownload(object sender, RoutedEventArgs e)
        {
            string[] Scopes = { DriveService.Scope.DriveReadonly };
            DriveService driveService = AuthenticateServiceAccount(@"C:\Users\210636\Downloads\licensemanage-cf129668e7ad.json", Scopes);
            FilesResource.ListRequest listRequest = driveService.Files.List();
            listRequest.Q = "'1Rl6E1sLkMdW0iRpfdrOzdF4C_U6lfZhu' in parents";
            listRequest.PageSize = 10;
            listRequest.Fields = "nextPageToken, files(id, name, size)";
            IList<Google.Apis.Drive.v3.Data.File> files = listRequest.Execute().Files;

            var fileId = "1QETWTnkIp9q6O35Rm99qC6LsJ4Gdg3I5";
            var request = driveService.Files.Get(fileId);
            request.Fields = "id, name, size";

            var file = request.Execute();
            long? fileSize = file.Size;
            string f = driveService.Files.Get(fileId).Execute().Name;

            var streamDownload = new MemoryStream();
            progressBar.Minimum = 0;
            progressBar.Maximum = 100;
            progressBar.Value = 50;
            request.MediaDownloader.ProgressChanged += (IDownloadProgress progress) =>
            {
                switch (progress.Status)
                {
                    case DownloadStatus.Downloading:
                        {
                            Dispatcher.BeginInvoke(new Action(() =>
                            {
                                progressBar.Value = Convert.ToDouble(progress.BytesDownloaded * 100 / fileSize);
                            }));
                            break;
                        }
                    case DownloadStatus.Completed:
                        {
                            Console.WriteLine("Download complete.");
                            using (FileStream fs = new FileStream("downloaded.zip", FileMode.OpenOrCreate))
                            {
                                streamDownload.WriteTo(fs);
                                fs.Flush();
                            }
                            break;
                        }
                    case DownloadStatus.Failed:
                        {
                            break;
                        }
                }
            };
            request.Download(streamDownload);
        }

        public static DriveService AuthenticateServiceAccount(string serviceAccountCredentialFilePath, string[] scopes)
        {
            GoogleCredential credential;
            using (var stream = new FileStream(serviceAccountCredentialFilePath, FileMode.Open, FileAccess.Read))
            {
                credential = GoogleCredential.FromStream(stream)
                     .CreateScoped(scopes);
            }

            // Create the  Analytics service.
            return new DriveService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = "Drive Service account Authentication Sample",
            });
        }

    }

Answer 1

request.Download(streamDownload); 正在阻止UI線程。 下載應該是async 。 我也強烈建議使用Progress<T>向UI報告進度： 4.5中的異步：在異步API中啟用進度和取消 。

MainWindow.xaml.cs

// Asynchronous event handler
private async void StartDownloadAsync(object sender, RoutedEventArgs e)
{
  ...

  var fileId = "1QETWTnkIp9q6O35Rm99qC6LsJ4Gdg3I5";

  progressBar.Minimum = 0;
  progressBar.Maximum = 100;
  progressBar.Value = 50;

  // Creating an instance of Progress<T> captures the current 
  // SynchronizationContext (UI context) to prevent cross threading when updating the ProgressBar
  IProgress<double> progressReporter = 
    new Progress<double>(value => progressBar.Value = value);

  await DownloadAsync(progressReporter, fileId);
}


private async Task DownloadAsync(progressReporter, string fileId)
{
  var streamDownload = new MemoryStream();

  var request = driveService.Files.Get(fileId);
  var file = request.Execute();
  long? fileSize = file.Size;

  // Report progress to UI via the captured UI's SynchronizationContext using IProgress<T>
  request.MediaDownloader.ProgressChanged += 
    (progress) => ReportProgress(progress, progressReporter, fileSize, streamDownload);

  // Execute download asynchronous
  await Task.Run(() => request.Download(streamDownload));
}


private void ReportProgress(IDownloadProgress progress, IProgress<double> progressReporter, long? fileSize, MemoryStream streamDownload)
{
  switch (progress.Status)
  {
    case DownloadStatus.Downloading:
    {
      double progressValue = Convert.ToDouble(progress.BytesDownloaded * 100 / fileSize);

      // Update the ProgressBar on the UI thread
      progressReporter.Report(progressValue);
      break;
    }
    case DownloadStatus.Completed:
    {
      Console.WriteLine("Download complete.");
      using (FileStream fs = new FileStream("downloaded.zip", FileMode.OpenOrCreate))
      {
        streamDownload.WriteTo(fs);
        fs.Flush();
      }
      break;
    }
    case DownloadStatus.Failed:
    {
      break;
    }
  }
}