DownloadFileAsync不工作/已调用.即使没有下载的文件，它也会跳过到DownloadCompleted

Question

我有问题。我使用的是Visual Studio 2013(Visual Basic(，在我的电脑上一切正常，但在其他电脑上则不然。

示例：没有调用client1.DownloadFileAsync，即使没有下载的文件，也会调用client1_DownloadCompleted。为什么跳过它！？

代码(在下载按钮上单击(：`

            AddHandler client1.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client1.DownloadFileCompleted, AddressOf client1_DownloadCompleted
            AddHandler client2.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client2.DownloadFileCompleted, AddressOf client2_DownloadCompleted
            AddHandler client3.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client3.DownloadFileCompleted, AddressOf client3_DownloadCompleted
            AddHandler client4.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client4.DownloadFileCompleted, AddressOf client1_DownloadCompleted
            AddHandler client5.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client5.DownloadFileCompleted, AddressOf client2_DownloadCompleted
            AddHandler client6.DownloadProgressChanged, AddressOf client_ProgressChanged
            AddHandler client6.DownloadFileCompleted, AddressOf client3_DownloadCompleted

            If CheckBox7.Checked Then
                odkoliko = odkoliko + 1
                Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
                client5.DownloadFileAsync(New Uri("https://dl.dropboxusercontent.com/s/7wq47s49aw5qrps/Obrisi%20PMF%20Novi%20Sad.lnk"), filePath5)
            End If
            If CheckBox4.Checked Then
                odkoliko = odkoliko + 1
                Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
                client4.DownloadFileAsync(New Uri("https://dl.dropboxusercontent.com/s/69q4pd281ka3lmf/Repair.exe"), filePath4)
            End If
            If CheckBox2.Checked Then
                odkoliko = odkoliko + 1
                Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
                client1.DownloadFileAsync(New Uri("https://dl.dropboxusercontent.com/s/u4iy3katgl394wf/PMF%20Novi%20Sad%20UPDATE.exe"), filePath1)
            End If
            If CheckBox5.Checked Then
                odkoliko = odkoliko + 1
                Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
                client2.DownloadFileAsync(New Uri("https://dl.dropboxusercontent.com/s/tuy0zspy1i1y84u/chatroom.html"), filePath2)
            End If
            If CheckBox3.Checked Then
                odkoliko = odkoliko + 1
                Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
                client6.DownloadFileAsync(New Uri("https://dl.dropboxusercontent.com/s/1n7oe7d1ms72qo3/Update.exe"), filePath6)
            End If
    End Select
End Sub
Private Sub client_ProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs)
End Sub
Private Sub client1_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Private Sub client2_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Private Sub client3_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Private Sub client4_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Private Sub client5_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Private Sub client6_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub
Public Sub AllDownloadFinished()
    If koliko > odkoliko Then
        Label6.Text = "GOTOVO!"
        ProgressBar1.Style = ProgressBarStyle.Continuous
        ProgressBar1.MarqueeAnimationSpeed = 0
        Panel1.Visible = False
        Panel2.Visible = False
        Panel3.Visible = True
    End If
End Sub`

正如我在电脑上说的那样，代码运行得很好，但在我朋友的电脑上却不行。也许问题不在代码中，而在中。NET框架、Visual c++Redistributable、Web Deployment或其他需要安装的Microsoft应用程序！？

Answer 1

您的代码没有检查异步错误。一旦您看到错误，就可以进行故障排除。

试试这个：

Private Sub client1_DownloadCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)
    If e.Error IsNot Nothing Then
        Msgbox(e.Error.Message)
        Exit Sub
    ElseIf e.Cancelled Then
        Msgbox("Cancelled")
        Exit Sub
    End If
    koliko = koliko + 1
    Label8.Text = "Popravlja se " & koliko & "/" & odkoliko & " stavka!"
    AllDownloadFinished()
End Sub

更多信息：http://msdn.microsoft.com/en-us/library/system.componentmodel.asynccompletedeventargs(v=vs.110(.aspx