DownloadFileAsync问题 [英] DownloadFileAsync Problem

问题描述

我有以下代码.它会下载FilesToDownload列表中的所有文件.我想使用DownloadFileAsync，因为这样我就可以使用进度条.但是，通过DownloadFileAsync，它将下载第一个文件并停止.如果我将其更改为DownloadFile，则可以正常工作，但不会显示进度.所以我的问题是如何多次使用DownloadFileAsync?完成后是否必须使用CancelAsync，然后重新启动?感谢您的帮助.

I have the following code. It downloads all the files in the list FilesToDownload. I want to use DownloadFileAsync because then I can use the the progressbar. However with DownloadFileAsync it will download the first file and stop. If I change it to DownloadFile it works fine but no progress is displayed. So my question is how do you use DownloadFileAsync multiple times? Do I have to use CancelAsync when its done and then start again? Any help is appreciated.

private void btnDownload_Click(object sender, RoutedEventArgs e)
        {
            choiceGrid.Visibility = Visibility.Hidden;
            if (FilesToDownload.Count > 0)
            {
                statusGrid.Visibility = Visibility.Visible;
                int updatesSelected = FilesToDownload.Count;
                int updateCounter = 0;
                XmlDocument xDoc = new XmlDocument();
                xDoc.Load(Properties.Settings.Default.optUpdatePath);
                WebClient clientDownloader = new WebClient();
                clientDownloader.DownloadProgressChanged += new DownloadProgressChangedEventHandler(clientDownloader_DownloadProgress);
                clientDownloader.DownloadFileCompleted += new System.ComponentModel.AsyncCompletedEventHandler(clientDownloader_DownloadCompleted);
                bool downloaded = false;
                bool found = false; 
                foreach (String filePath in FilesToDownload)
                {
                    foreach (XmlNode xNode in xDoc.DocumentElement.ChildNodes)
                    {
                        if (!found)
                        {
                            if (xNode.Name == "Picture")
                            {
                                foreach (XmlNode xNode2 in xNode.ChildNodes)
                                {
                                    if (xNode2.Name == "Path")
                                    {
                                        if (xNode2.InnerText == filePath)
                                        {
                                            found = true;
                                            try
                                            {
                                                if (!File.Exists(Properties.Settings.Default.contentFilePath + Path.GetFileName(filePath)))
                                                {
                                                    lblFileCount.Content = "Working on update " + (updateCounter + 1) + " of " + updatesSelected;
                                                    lblActiveFile.Content = filePath;
                                                    clientDownloader.DownloadFile(new Uri(filePath), Properties.Settings.Default.contentFilePath + Path.GetFileName(filePath));                                                    
                                                    downloaded = true;
                                                }
                                            }
                                            catch
                                            {
                                                downloaded = false;
                                            }
                                        }
                                        if (downloaded)
                                        {
                                            xNode2.InnerText = Properties.Settings.Default.contentFilePath + Path.GetFileName(filePath);
                                            AddUpdateNode(xNode);
                                            updateCounter++;
                                        }
                                    }
                                }                                
                            }
                        }
                        downloaded = false;
                    }
                    found = false;
                }
                clientDownloader.Dispose();
                lblActiveFile.Content = "Finished Downloading Updates!";
                lblFileCount.Content = updateCounter + " of " + updatesSelected + " updates have been downloaded and installed.";
                FilesToDownload.Clear();
            }
            else
            {
                MessageBox.Show("Nothing was selected to download.");
            }
        }




        void clientDownloader_DownloadProgress(object sender, DownloadProgressChangedEventArgs e)
        {
            prgBar.Value = e.ProgressPercentage;
        }

        void clientDownloader_DownloadCompleted(object sender, AsyncCompletedEventArgs e)
        {
            prgBar.Value = 100;
        }

推荐答案

 
if (FilesToDownload.Count > 0)
            {

and end of the if statement place in a new method which you will call on different threads for each file that you want to download.

and end of the if statement place in a new method which you will call on different threads for each file that you want to download.

Have a look at this example I wrote:

Have a look at this example I wrote:

http://code.msdn.microsoft.com/CCS-LABS-Windows-Forms-Web-4a18db8d

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