Question

我有一张表格，我从中下载文件。我有一个单独的类（download.cs）来处理文件的下载和进度等。我无法解决如何在文件完成后运行该文件。我可以看到下载后运行的事件，但此时我想恢复调用例程中正在进行的操作。

Form1.cs的

  private void btnDownloadProfile_Click(object sender, EventArgs e)
            {
                tc.SelectTab("tabLog");
                Download d = new Download();
                d.DownloadFile("http://www.****.com/Downloads/***.zip", appPath + @"Files\***.zip", "Filename");
                //At this point i'd like to wait for the download to finish and then execute the download
            }

Download.cs

 WebClient webClient; 
        public void DownloadFile(String URL, String Path, String Name)
        {
            using (webClient = new WebClient())
            {
                webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
                webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
                Uri Link = new System.Uri(URL);
                try
                {
                    Log.addLog("Attempting to download: " + Name);
                    webClient.DownloadFileAsync(Link, Path);       
                }
                catch (Exception ex)
                {
                    Log.addLog(ex.Message);
                }
            }
        }

        private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        { 
           Log.addLog(e.ProgressPercentage.ToString() + "%");
        }

        private void Completed(object sender, AsyncCompletedEventArgs e)
        {
            if (e.Cancelled == true)
            {
                Log.addLog("Download has been canceled.");
            }
            else
            {
                Log.addLog("Download completed!");
            }
        }

修改为了澄清。单击该按钮后，该事件将在Form1.cs上运行，从而启动下载。然后使用Async内容进入后台并自由启动UI。我可以在日志文件中看到发生的下载。一旦Compelted项在Download.cs中运行，我就可以告诉该文件已经完成下载。但是，我在那时似乎无法确定哪个文件已经完成下载，它只是告诉我一个文件已下载。我怎样才能传递给完成文件名，或者在btnDownloadProfile_Click上保留事件，直到文件完成后才能使用它。

Answer 1

据我所知，你想下载文件，然后继续调用下载方法...如果这是正确的，你可以使用带有async / await的TaskCompletionSource类

（顺便说一句：如果显示下载进度，则可以使用DownloadFileTaskAsync

用法：

async void YourMethod()
{

    var dl = new SODownloader();
    await dl.DownloadFile(........);
    //Do whatever you want to do. Download is finsished....            
}

您修改的下载程序类

using System;
using System.ComponentModel;
using System.Diagnostics;
using System.Net;
using System.Threading.Tasks;

namespace SO3
{
    public class SODownloader
    {
        WebClient webClient;
        TaskCompletionSource<object> tcs = new TaskCompletionSource<object>(); //<-----

        public Task DownloadFile(String URL, String Path, String Name)
        {

            using (webClient = new WebClient())
            {
                webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
                webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
                Uri Link = new System.Uri(URL);
                try
                {
                    Debug.WriteLine("Attempting to download: " + Name);
                    webClient.DownloadFileAsync(Link, Path);
                }
                catch (Exception ex)
                {
                    Debug.WriteLine(ex.Message);
                }
            }

            return tcs.Task; //<-----
        }

        private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            Debug.WriteLine(e.ProgressPercentage.ToString() + "%");
        }

        private void Completed(object sender, AsyncCompletedEventArgs e)
        {

            if (e.Cancelled == true)
            {
                tcs.TrySetException(new TaskCanceledException("Download has been canceled.")); //<-----
                Debug.WriteLine("Download has been canceled.");
            }
            else
            {
                tcs.TrySetResult("Download completed!"); //<-----
                Debug.WriteLine("Download completed!");
            }
        }
    }
}

下载后，从课程中运行下载的文件

1 个答案: