c# - 如何使用 Async/Await 进行进度报告

Question

假设我有一个文件列表，我必须使用 c# 项目中的 ftp 相关类将这些文件复制到 Web 服务器。在这里我想使用 Async/Await 功能，还想显示多个进度条以同时上传多个文件。每个进度条指示每个文件的上传状态。所以请指导我该怎么做。

当我们与后台 worker 一起做这种工作时，这很容易，因为后台 worker 有进度变化事件。那么如何使用 Async/Await 处理这种情况。如果可能的话，用示例代码指导我。谢谢

Answer 1

来自 article 的示例代码

public async Task<int> UploadPicturesAsync(List<Image> imageList, 
     IProgress<int> progress)
{
      int totalCount = imageList.Count;
      int processCount = await Task.Run<int>(() =>
      {
          int tempCount = 0;
          foreach (var image in imageList)
          {
              //await the processing and uploading logic here
              int processed = await UploadAndProcessAsync(image);
              if (progress != null)
              {
                  progress.Report((tempCount * 100 / totalCount));
              }
              tempCount++;
          }
          return tempCount;
      });
      return processCount;
}

private async void Start_Button_Click(object sender, RoutedEventArgs e)
{
    int uploads=await UploadPicturesAsync(GenerateTestImages(),
        new Progress<int>(percent => progressBar1.Value = percent));
}

如果您想独立报告每个文件，您将有不同的 IProgress 基本类型:

public Task UploadPicturesAsync(List<Image> imageList, 
     IProgress<int[]> progress)
{
      int totalCount = imageList.Count;
      var progressCount = Enumerable.Repeat(0, totalCount).ToArray(); 
      return Task.WhenAll( imageList.map( (image, index) =>                   
        UploadAndProcessAsync(image, (percent) => { 
          progressCount[index] = percent;
          progress?.Report(progressCount);  
        });              
      ));
}

private async void Start_Button_Click(object sender, RoutedEventArgs e)
{
    int uploads=await UploadPicturesAsync(GenerateTestImages(),
        new Progress<int[]>(percents => ... do something ...));
}