如何使用vb.net在列表框中下载多个文件

Question

我想下载多个文件和列表框中的下载链接有没有办法使用WebClient做到这一点，我看到人们通过逐个文件下载来做到这一点，看起来很难，我想显示当前下载速度，当前文件大小和总工艺进度

Answer 1

我用这种方法解决了这个问题:

Imports System.Net
Public Class Form1
Private WithEvents DonloadFile As WebClient
Dim stopwatch As Stopwatch = New Stopwatch
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
ListBox1.SelectedIndex = 0
End Sub
Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged
stopwatch.Start()
DonloadFile = New WebClient
Try
DonloadFile.DownloadFileAsync(New Uri(ListBox1.SelectedItem.ToString), "C:Users" & Environment.UserName & "Desktop" & IO.Path.GetFileName(ListBox1.SelectedItem.ToString))
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End Sub
Private Sub DonloadFile_DownloadProgressChanged(sender As Object, e As DownloadProgressChangedEventArgs) Handles DonloadFile.DownloadProgressChanged
Dim y As Integer = (e.BytesReceived / 1024) / 1024
Label6.Text = "Download Speed: " & String.Format("{0} MB/s", (y / (stopwatch.Elapsed.TotalSeconds)).ToString("0.00"))
Label2.Text = "Current File Size: " & Math.Round(e.TotalBytesToReceive / (1024 * 1024), 1) & " MB"
Label3.Text = "Current File Persent: " & e.ProgressPercentage
Label1.Text = "Total Files: " & ListBox1.Items.Count.ToString()
If ListBox1.Items.Count.ToString > (ListBox1.SelectedIndex + 1) Then
If e.ProgressPercentage = 100 Then
ListBox1.SelectedIndex += 1
End If
Else
MessageBox.Show("Download completed successful", "Info")
End If
End Sub
Private Sub DonloadFile_DownloadDataCompleted(sender As Object, e As DownloadDataCompletedEventArgs) Handles DonloadFile.DownloadDataCompleted
stopwatch.Reset()
End Sub
End Class

感谢@Fawlty

Answer 2

我编写了一些代码来演示如何做到这一点。我创建了一个FileDownloader类，因为这将允许您在下载完成时获得源url和目标文件名。我还添加了一个事件的进展。单独使用WebClient类的问题是，您无法跟踪事件中正在处理的文件。

Imports System.ComponentModel
Imports System.Net
' A class for downloading files, with progress and finished events
Public Class FileDownloader
' Private storage
Private FileURL As String = ""
Private SaveToPath As String = ""
' A class to return our result in
Public Class FileDownloaderFileDownloadedEventArgs
Public Property DownloadedURL As String
Public Property SaveToPath As String
Public Sub New(DownloadedURL As String, SaveToPath As String)
Me.DownloadedURL = DownloadedURL
Me.SaveToPath = SaveToPath
End Sub
End Class
' A class to show progress
Public Class FileDownloaderProgressEventArgs
Public Property DownloadURL As String
Public Property SaveToPath As String
Public Property TotalBytes As Long
Public Property ProgressBytes As Long
Public Property ProgressPercent As Integer
Public Property UserState As Object
Public Sub New(DownloadURL As String, SaveToPath As String, TotalBytes As Long, ProgressBytes As Long, ProgressPercent As Integer, UserState As Object)
Me.DownloadURL = DownloadURL
Me.SaveToPath = SaveToPath
Me.TotalBytes = TotalBytes
Me.ProgressBytes = ProgressBytes
Me.ProgressPercent = ProgressPercent
Me.UserState = UserState
End Sub
End Class
' The event to raise when the file is downloaded
Public Event FileDownloaded(sender As Object, e As FileDownloaderFileDownloadedEventArgs)
' The event to raise when there is progress
Public Event Progress(sender As Object, e As FileDownloaderProgressEventArgs)
' Pass in the URL and FilePath when creating the downloader object
Public Sub New(FileURL As String, SaveToPath As String)
Me.FileURL = FileURL
Me.SaveToPath = SaveToPath
End Sub
' Call Download() to do the work
Public Sub Download()
Using wc As New WebClient
AddHandler wc.DownloadFileCompleted, AddressOf DownloadFileCompleted
AddHandler wc.DownloadProgressChanged, AddressOf DownloadProgressChanged
wc.DownloadFileAsync(New Uri(FileURL), SaveToPath)
End Using
End Sub
' Catch the download complete and raise our event
Private Sub DownloadProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs)
RaiseEvent Progress(Me, New FileDownloaderProgressEventArgs(FileURL, SaveToPath, e.TotalBytesToReceive, e.BytesReceived, e.ProgressPercentage, e.UserState))
End Sub
Private Sub DownloadFileCompleted(sender As Object, e As AsyncCompletedEventArgs)
' Some code you want to run after each file has downloaded
RaiseEvent FileDownloaded(Me, New FileDownloaderFileDownloadedEventArgs(FileURL, SaveToPath))
End Sub
End Class
#Region "How to use the FileDownloader class"
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
' Loop the URLs in the ListBox
For Each item In ListBox1.Items
' Create a FileDownloader object to handler each one
Dim FD = New FileDownloader(item, "c:temp" & IO.Path.GetFileName(item))
' Attach the event handlers
AddHandler FD.FileDownloaded, AddressOf FileDownloaded
AddHandler FD.Progress, AddressOf Progress
' Start the download
FD.Download()
Next
End Sub
' Event handler for file download completed
Private Sub FileDownloaded(sender As Object, e As FileDownloader.FileDownloaderFileDownloadedEventArgs)
tb_Log.AppendText(e.DownloadedURL & "  Downloaded To:  " & e.SaveToPath & vbCrLf)
End Sub
' Event handler for progress
Private Sub Progress(sender As Object, e As FileDownloader.FileDownloaderProgressEventArgs)
tb_Log.AppendText(IO.Path.GetFileName(e.DownloadURL) & " " & e.ProgressPercent & "% downloaded" & vbCrLf)
End Sub
#End Region