Question

我正在制作一个自动文件下载器，当我按下按钮时，我需要它重新下载并覆盖文件。

这是我的代码：

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
  My.Computer.Network.DownloadFile _
    ("http://www.randomurl.com/randomfile.txt", _
    Path.Combine(Environment.GetFolderPath( _
    Environment.SpecialFolder.ApplicationData), _
    "test/randomfile.txt"))
End Sub

Answer 1

DownloadFile存在重载，允许覆盖上一个文件

 My.Computer.Network.DownloadFile 
       (address, destinationFileName, userName,
        password, showUI, connectionTimeout, overwrite)

来自MSDN

address = String或Uri。要下载的文件的路径，包括文件姓名和主持人地址。必需的。
destinationFileName = String。下载的文件名和路径文件。必需的。
userName = String。要进行身份验证的用户名。默认为空 string，“”。
password = String.Password进行身份验证。默认是一个空字符串， “”。
showUI = Boolean。指定是否显示进度操作。默认值为False。
connectionTimeout = Int32。超时间隔，以毫秒为单位。默认是100秒。
overwrite =布尔值。指定是否覆盖现有文件。默认值为False。

因此，您可以通过这种方式更改代码

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
  My.Computer.Network.DownloadFile _
    (address := "http://www.randomurl.com/randomfile.txt", _
    destinationFileName := Path.Combine(Environment.GetFolderPath( _
    Environment.SpecialFolder.ApplicationData), _
    "test/randomfile.txt"), _
    userName := string.Empty, password := string.Empty, _
    showUI := False, connectionTimeout := 100000, _
    overwrite := True)
End Sub

Answer 2

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim uri As System.Uri = New System.Uri("http://www.randomurl.com/randomfile.txt")
    Dim webclient As System.Net.WebClient = New System.Net.WebClient()

    Dim path As String = New String(System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "test\\randomfile.txt"))
    Dim fileInfo As System.IO.FileInfo = New System.IO.FileInfo(path)
    If Not System.IO.Directory.Exists(fileInfo.Directory.FullName) Then
        System.IO.Directory.CreateDirectory(fileInfo.Directory.FullName)
    End If

    AddHandler webclient.DownloadFileCompleted, AddressOf webclient_DownloadDataCompleted

    webclient.DownloadFileAsync(uri, path)

End Sub


Private Sub webclient_DownloadDataCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs)

    MessageBox.Show("Your download has completed.")

End Sub

（编辑 - 更改为显示评论中请求的异步方法）

请注意，如果文件存在，该文件将被覆盖 - ＆gt; http://msdn.microsoft.com/en-us/library/ez801hhe(v=VS.80).aspx

如何覆盖下载的文件vb.net

2 个答案: