Question

用于开始下载的按钮点击事件

private void btnStart_Click(object sender, EventArgs e)
        {
            downloadFile(links);           
        }

links是一个列表，里面有一些http链接。

WebClient事件

private void downloadFile(IEnumerable<string> urls)
        {
            foreach (var url in urls)
            {
                _downloadUrls.Enqueue(url);
            }

            // Starts the download
            btnStart.Text = "Downloading...";
            btnStart.Enabled = false;
            pBarFileProgress.Visible = true;

            DownloadFile();

            label2.Visible = true;
            label3.Visible = true;
            label4.Visible = true;
            label7.Visible = true;
            label3.Text = "";
            label7.Text = "";
            label2.Text = "";
            label4.Text = "";
        }

        private void DownloadFile()
        {
            if (_downloadUrls.Any())
            {
                client.DownloadProgressChanged += client_DownloadProgressChanged;
                client.DownloadFileCompleted += client_DownloadFileCompleted;

                url = _downloadUrls.Dequeue();

                if (url.Contains("animated") && url.Contains("infra"))
                {
                    string startTag = "animated/";
                    string endTag = "/infra";

                    int index = url.IndexOf(startTag);
                    int index1 = url.IndexOf(endTag);

                    fname = url.Substring(index + 9, index1 - index - 9);
                    var countryName = codeToFullNameMap[fname];
                    downloadDirectory = tbxMainDownloadPath.Text;
                    downloadDirectory = Path.Combine(downloadDirectory, countryName);
                }
                else
                {
                    fname = "Tempfile";
                    downloadDirectory = tbxMainDownloadPath.Text;
                }

                client.DownloadFileAsync(new Uri(url), downloadDirectory + "\\" + fname + ".gif", url);
                lastDownloadedFile = downloadDirectory + "\\" + fname + ".gif";

                return;
            }

            // End of the download
            label2.Text = "All files have been downloaded";
        }

        private void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
        {
            if (e.Cancelled)
            {
                tracker.NewFile();
                DownloadFile();
                return;
                // handle cancelled scenario
            }
            if (e.Error != null)
            {
                // handle error scenario
                throw e.Error;
            }

            label2.Text = "Download Complete";

            string lastUrl = (string)e.UserState;

            listView1.BeginUpdate();
            foreach (ListViewItem li in listView1.Items)
            {
                if (li.SubItems[2].Text == lastUrl)
                {
                    li.SubItems[0].Text = "Downloaded";
                    li.SubItems.Add("Color");
                    li.SubItems[0].ForeColor = Color.Green;
                    li.UseItemStyleForSubItems = false;
                }
            }
            listView1.EndUpdate();

            tracker.NewFile();
            DownloadFile();
        }

        void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            tracker.SetProgress(e.BytesReceived, e.TotalBytesToReceive);
            pBarFileProgress.Value = (int)(tracker.GetProgress() * 100.0);
            label3.Text = e.BytesReceived + "/" + e.TotalBytesToReceive;
            label7.Text = tracker.GetBytesPerSecondString();
            label2.Text = "Downloading";
            label4.Text = downloadDirectory + "\\" + fname + ".gif";
        }

例外是在第178行

client.DownloadFileAsync(new Uri(url), downloadDirectory + "\\" + fname + ".gif", url);

第233行已完成事件：

DownloadFile();

我尝试谷歌在许多答案中说它在运行新的webclient请求之前尚未完成下载。我确定它是否正在完成事件'意味着当前下载完成没有？

我该如何解决和处理这个例外？

例外：

块引用的InnerException：的HResult = -2146233067 Message = WebClient不支持并发I / O操作。来源=系统堆栈跟踪：在System.Net.WebClient.ClearWebClientState（）在System.Net.WebClient.DownloadFileAsync（Uri地址，String fileName，Object userToken）在Form1.cs中的DownloadMultipleFiles.Form1.DownloadFile（）：第178行在Form1.cs中的DownloadMultipleFiles.Form1.client_DownloadFileCompleted（Object sender，AsyncCompletedEventArgs e）：第233行 at System.ComponentModel.AsyncCompletedEventHandler.Invoke（Object sender，AsyncCompletedEventArgs e）在System.Net.WebClient.OnDownloadFileCompleted（AsyncCompletedEventArgs e）在System.Net.WebClient.DownloadFileOperationCompleted（Object arg） InnerException：

Answer 1

调用

的等待方法

client.DownloadFileAsync(new Uri(url), downloadDirectory + "\\" + fname + ".gif", url).Wait();

试一试

当使用WebClient下载文件时我得到异常不支持并发I / O操作我该如何解决？

1 个答案: