如何覆蓋下載的文件vb.net

Question

我正在製作一個自動文件下載器，我需要它來重新下載並覆蓋文件，當我按下按鈕時。

這裏是我的代碼：

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

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 

（編輯 - 更改爲顯示在意見中的要求異步方法），該文件將是否被覆蓋

注它存在 - >http://msdn.microsoft.com/en-us/library/ez801hhe(v=VS.80).aspx

Answer 2

沒有爲DownloadFile過載，使以前的文件

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

的覆蓋作爲從MSDN

• 地址=字符串或URI。要下載的文件的路徑，包括文件名稱和主機地址 。需要。
• destinationFileName = String。下載的 文件的文件名和路徑。需要。
• userName = String。用戶名進行身份驗證。缺省值是一個空的 字符串，「」。
• password =要認證的String.Password。默認值爲空字符串，「 」。
• showUI = Boolean.Specifications是否顯示 操作的進度。默認值是False。
• connectionTimeout = Int32。超時間隔，以毫秒爲單位。默認 是100秒。
• overwrite = Boolean。指定是否覆蓋現有文件。 默認爲False。

這樣，就可以用這種方法改變你的代碼

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