Question

我尝试编写应用程序来下载2个文件，我可以使用以下代码下载2个文件：

        Dim client As WebClient = New WebClient
        AddHandler client.DownloadProgressChanged, AddressOf client_ProgressChanged
        AddHandler client.DownloadFileCompleted, AddressOf client_DownloadCompleted
        client.DownloadFileAsync(New Uri("http://URL.com/Myfile.exe"), "..\MyFile.exe")
        Button1.Text = "Download in Progress"
        Button1.Enabled = False

        Dim client2 As WebClient = New WebClient
        AddHandler client2.DownloadProgressChanged, AddressOf client_ProgressChanged
        AddHandler client2.DownloadFileCompleted, AddressOf client_DownloadCompleted
        client2.DownloadFileAsync(New Uri("http://URL.com/Myfile2.exe"), "..\MyFile2.exe")

我遇到的问题是进度条没有显示两个文件的总下载进度。它会显示一个，然后几秒钟后会显示另一个并继续在两者之间切换。

Private Sub client_ProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs)
    Dim bytesIn As Double = Double.Parse(e.BytesReceived.ToString())
    Dim totalBytes As Double = Double.Parse(e.TotalBytesToReceive.ToString())
    Dim percentage As Double = bytesIn / totalBytes * 100
    ProgressBar.Value = Int32.Parse(Math.Truncate(percentage).ToString())
    Label1.Text = "Downloaded: " & bytesIn & " of " & totalBytes
    Label2.Text = String.Format("{0:00}", percentage) & "%"
End Sub

任何人都知道如何让进度条结合两个下载的值？或者也许我可以告诉它等待第一次下载然后开始第二次？

Answer 1

您只需跟踪每个WebClient的进度。总进展将达到200％。解决一般情况：

Dim progress As Dictionary(Of WebClient, Integer)

Sub StartDownloads()
     progress = new Dictionary(Of WebClient, Integer)
     Dim client As WebClient = New WebClient()
     progress.Add(client, 0)
     '' etc..
End Sub

Private Sub client_ProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs)
    progress(DirectCast(sender, WebClient)) = e.ProgressProcent
    Dim total As Integer = 0
    For Each client In progress.Keys
        total += progress(client)
    Next
    ProgressBar.Value = total \ progress.Count
End Sub

未经测试，应该接近。

Answer 2

要使其一次加载一个文件，请对所有文件名使用List(Of String)。使用第一个元素（文件名）启动该过程使用已完成的事件，并删除该文件名和已完成事件的addhandler。然后检查List(Of String)中是否有更多文件，然后为该网络充电新的WebClient - 冲洗重复。

Private files As New List(Of String)
'fill this with the file names(URIs) then start the process
Private Sub DownloadFile()
   Dim client As New WebClient
   AddHandler client.DownloadProgressChanged, AddressOf client_ProgressChanged
   AddHandler client.DownloadFileCompleted, AddressOf client_DownloadCompleted
   client.DownloadFileAsync(New Uri(files(0), "some destination path")
End Sub

Private Sub client_DownloadCompleted(...)
   RemoveHandler client.DownloadProgressChanged, AddressOf client_ProgressChanged
   RemoveHandler client.DownloadFileCompleted, AddressOf client_DownloadCompleted
   files.RemoveAt(0)
   If files.Count > 0 Then DownloadFile()
End Sub

VB.NET AddHandler下载多个文件的进度

2 个答案: