VB.Net程序设计:多任务文件下载

2009-03 想写一个自动更新系统，就必须要用到下载这个功能。 先在这里练习一下。呵呵。

界面：

--

主要程序代码：

Private Sub BtnStartDownload_Click(ByVal sender As Sy<a href="https://www.jb51.cc/tag/stem/" target="_blank" class="keywords">stem</a>.Object,ByVal e As Sy<a href="https://www.jb51.cc/tag/stem/" target="_blank" class="keywords">stem</a>.EventArgs) Handles BtnStartDownload.Click iCount = Me.Lst<a href="https://www.jb51.cc/tag/Box/" target="_blank" class="keywords">Box</a>FileList.Items.Count If iCount > 0 Then If Me.BtnStartDownload.Text.Equals("开始下载") Then Me.isCancelDownLoad = False Dim t As Thread = New Thread(New ThreadStart(AddressOf DownLoadFile)) t.IsBackground = True t.Name = "DownLoadFile" t.Start() Me.BtnStartDownload.Text = "取消下载任务" Else Me.isCancelDownLoad = True If myWebClient IsNot <a href="https://www.jb51.cc/tag/nothing/" target="_blank" class="keywords">nothing</a> Then myWebClient.CancelAsync() evtPerDonwload.Set() End If ResetDownLoadPrg() Me.BtnStartDownload.Text = "开始下载" End If Else Me.BtnStartDownload.Text = "开始下载" ShowMsg("<a href="https://www.jb51.cc/tag/xiazailiebiao/" target="_blank" class="keywords">下载列表</a>没有任务。") End If End Sub Private Sub DownLoadFile() Dim i As Integer = 0 Dim SaveFolder,FileFullPath,FileName,url As String evtPerDonwload = New ManualResetEvent(False) SaveFolder = Me.Txt<a href="https://www.jb51.cc/tag/Box/" target="_blank" class="keywords">Box</a>SaveFolder.Text For i = 0 To iCount - 1 If Me.isCancelDownLoad Then Exit For url = Me.Lst<a href="https://www.jb51.cc/tag/Box/" target="_blank" class="keywords">Box</a>FileList.Items(i).ToString FileName = IO.Path.GetFileName(url) If SaveFolder = "" Then '如果是保存路径=空路径，就使用虚拟路径，下载到当前程序的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>夹里面。 FileFullPath = FileName Else '否则，保存到<a href="https://www.jb51.cc/tag/yonghu/" target="_blank" class="keywords">用户</a>选择的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>夹里面。 FileFullPath = IO.Path.Combine(SaveFolder,FileName) End If Me.SmoothProgressBar1.Value = 0 myWebClient = New WebClient() AddHandler myWebClient.DownloadProgressChanged,AddressOf OnDownloadProgressChanged AddHandler myWebClient.DownloadFileCompleted,AddressOf OnDownloadFileCompleted evtPerDonwload.Reset() '<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>保存在当前目录下. myWebClient.DownloadFileAsync(New Uri(url),FileName) '等待下载完成 evtPerDonwload.WaitOne() myWebClient.<a href="https://www.jb51.cc/tag/dis/" target="_blank" class="keywords">dis</a>pose() myWebClient = <a href="https://www.jb51.cc/tag/nothing/" target="_blank" class="keywords">nothing</a> Next '这里可以不用到这个，因为每次完成下载都会设置一次。加了反而会出现bug: 无法重设。 'ResetDownLoadPrg() 'If Me.isCancelDownLoad = False Then ResetDownLoadBtn() ' End If End Sub Private Sub OnDownloadProgressChanged(ByVal sender As Object,ByVal e As Sy<a href="https://www.jb51.cc/tag/stem/" target="_blank" class="keywords">stem</a>.Net.DownloadProgressChangedEventArgs) '因为每一次下载<a href="https://www.jb51.cc/tag/yige/" target="_blank" class="keywords">一个</a><a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>时候都是New<a href="https://www.jb51.cc/tag/yige/" target="_blank" class="keywords">一个</a>WebClient所以事件要动态<a href="https://www.jb51.cc/tag/tianjia/" target="_blank" class="keywords">添加</a>到相对应的实例中。AddHandler ...OnDownloadProgressChanged '不可以用Handles myWebClient.DownloadProgressChanged此<a href="https://www.jb51.cc/tag/fangfa/" target="_blank" class="keywords">方法</a>只可以用在 Dim WithEvents myWebClient 相当于静态的控件 ShowMsg(String.Format("正在下载:{0},下载:{1}/{2}",e.UserState.ToString,FileHelper.FormatFileSize(e.BytesReceived),FileHelper.FormatFileSize(e.TotalBytesToReceive))) Me.SmoothProgressBar1.Value = e.Progre<a href="https://www.jb51.cc/tag/ssp/" target="_blank" class="keywords">ssp</a>ercentage 'e.BytesReceived是接受<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>的bytes 'e.TotalBytesToReceive是<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>的总大小 'e.Progre<a href="https://www.jb51.cc/tag/ssp/" target="_blank" class="keywords">ssp</a>ercentage 是当前下载进度 End Sub Private Sub OnDownloadFileCompleted(ByVal sender As Object,ByVal e As Sy<a href="https://www.jb51.cc/tag/stem/" target="_blank" class="keywords">stem</a>.ComponentModel.AsyncCompletedEventArgs) '因为每一次下载<a href="https://www.jb51.cc/tag/yige/" target="_blank" class="keywords">一个</a><a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>时候都是New<a href="https://www.jb51.cc/tag/yige/" target="_blank" class="keywords">一个</a>WebClient所以事件要动态<a href="https://www.jb51.cc/tag/tianjia/" target="_blank" class="keywords">添加</a>到相对应的实例中。AddHandler ...OnDownloadFileCompleted '不可以用Handles myWebClient.DownloadFileCompleted此<a href="https://www.jb51.cc/tag/fangfa/" target="_blank" class="keywords">方法</a>只可以用在 Dim WithEvents myWebClient 相当于静态的控件 '发出释放同步进程信号 evtPerDonwload.Set() '重设下载进度信息和进度条 ResetDownLoadPrg() 'If Me.isCancelDownLoad = False Then ' If e.Error Is <a href="https://www.jb51.cc/tag/nothing/" target="_blank" class="keywords">nothing</a> Then ' ShowMsg("下载完毕" & e.UserState.ToString()) ' Else ' ShowMsg("未完成下载: " & e.Error.Message) ' End If 'End If End Sub