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VB プログラムでファイルのダウンロードを一時停止する方法はありますか?? http メソッドと my.computer.net メソッドの両方を試しましたが、うまくいきませんでした。また、この方法でバックグラウンド ワーカーを一時停止しようとしました: [URL] しかし、bgworker が一時停止されてもダウンロードは続行されます.....

Dim locationfiledownload As String
Dim whereToSave As String 'Where the program save the file

Delegate Sub ChangeTextsSafe(ByVal length As Long, ByVal position As Integer, ByVal percent As Integer, ByVal speed As Double)
Delegate Sub DownloadCompleteSafe(ByVal cancelled As Boolean)

Public Sub DownloadComplete(ByVal cancelled As Boolean)
    ToolStripButton2.Enabled = True
    ToolStripButton3.Enabled = False

    If cancelled Then
        Me.Label4.Text = "Cancelled"
        MessageBox.Show("Download aborted", "Aborted", MessageBoxButtons.OK, MessageBoxIcon.Information)
    Else
        Me.Label4.Text = "Successfully downloaded"
        MessageBox.Show("Successfully downloaded!", "All OK", MessageBoxButtons.OK, MessageBoxIcon.Information)
    End If

    Me.RadProgressBar1.Value1 = 0
    Me.Label4.Text = ""

End Sub

Public Sub ChangeTexts(ByVal length As Long, ByVal position As Integer, ByVal percent As Integer, ByVal speed As Double)
    Me.Label4.Text = "Downloaded " & Math.Round((position / 1024), 2) & " KB of " & Math.Round((length / 1024), 2) & "KB"
    Me.RadProgressBar1.Value1 = percent
End Sub

Public Sub btnDownload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ToolStripButton2.Click
    locationfiledownload = GetPage("http://asankonkur.ir/update/locationfiledownload.txt")

    If locationfiledownload <> "" AndAlso locationfiledownload.StartsWith("http://") Then

        Me.SaveFileDialog1.FileName = locationfiledownload.Split("/"c)(locationfiledownload.Split("/"c).Length - 1)
        If Me.SaveFileDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then
            Me.whereToSave = Me.SaveFileDialog1.FileName
            Me.SaveFileDialog1.FileName = ""

            ToolStripButton2.Enabled = False
            ToolStripButton3.Enabled = True

            Me.BackgroundWorker2.RunWorkerAsync() 'Start download
        End If
    Else
        MessageBox.Show("Please insert valid URL for download", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning)
    End If
End Sub

Private Sub BackgroundWorker2_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker2.DoWork
    'Creating the request and getting the response
    Dim theResponse As HttpWebResponse
    Dim theRequest As HttpWebRequest
    Try 'Checks if the file exist

        theRequest = WebRequest.Create(locationfiledownload)
        theResponse = theRequest.GetResponse
    Catch ex As Exception

        MessageBox.Show("An error occurred while downloading file. Possibe causes:" & ControlChars.CrLf & _
                        "1) File doesn't exist" & ControlChars.CrLf & _
                        "2) Remote server error", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

        Dim cancelDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
        Me.Invoke(cancelDelegate, True)

        Exit Sub
    End Try
    Dim length As Long = theResponse.ContentLength 'Size of the response (in bytes)

    Dim safedelegate As New ChangeTextsSafe(AddressOf ChangeTexts)
    Me.Invoke(safedelegate, length, 0, 0, 0) 'Invoke the TreadsafeDelegate

    Dim writeStream As New IO.FileStream(Me.whereToSave, IO.FileMode.Create)
    'Replacement for Stream.Position (webResponse stream doesn't support seek)
    Dim nRead As Integer
    'To calculate the download speed
    Dim speedtimer As New Stopwatch
    Dim currentspeed As Double = -1
    Dim readings As Integer = 0

    Do
        If BackgroundWorker2.CancellationPending Then 'If user abort download
            Exit Do
        End If
        speedtimer.Start()
        Dim readBytes(4095) As Byte
        Dim bytesread As Integer = theResponse.GetResponseStream.Read(readBytes, 0, 4096)

        nRead += bytesread
        Dim percent As Short = (nRead * 100) / length

        Me.Invoke(safedelegate, length, nRead, percent, currentspeed)

        If bytesread = 0 Then Exit Do

        writeStream.Write(readBytes, 0, bytesread)

        speedtimer.Stop()

        readings += 1
        If readings >= 5 Then 'For increase precision, the speed it's calculated only every five cicles
            currentspeed = 20480 / (speedtimer.ElapsedMilliseconds / 1000)
            speedtimer.Reset()
            readings = 0
        End If
    Loop
    'Close the streams
    theResponse.GetResponseStream.Close()
    writeStream.Close()
    If Me.BackgroundWorker2.CancellationPending Then
        IO.File.Delete(Me.whereToSave)
        Dim cancelDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
        Me.Invoke(cancelDelegate, True)
        Exit Sub
    End If

    Dim completeDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
    Me.Invoke(completeDelegate, False)

End Sub

Private Sub mainForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Me.Label4.Text = ""
End Sub

Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ToolStripButton3.Click
    Me.BackgroundWorker2.CancelAsync() 'Send cancel request
End Sub
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1 に答える 1

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あなたのコードでは、を使用してWebRequest.Create(locationfiledownload)います。デフォルトでは、これにより、ファイル全体を要求するリクエスト ヘッダーが作成されます。リクエストを編集し、探しているファイルの特定のバイト範囲を要求する Range ヘッダーを追加する必要があります。たとえば、WebRequest.Headers.Range.Rangesコレクションに追加します。残念ながら、既にダウンロードされているものの詳細をどこかに保存する必要があるため、コードがかなり複雑になります (アプリケーションの終了/再起動後に再開したい場合)。知っておく必要があります。

  1. すでにダウンロードされているファイルの量 (存在する場合)
  2. 一度にダウンロードする予定の量

これがわかったら、ファイルの X バイトの Range ヘッダーを使用してリクエストを作成する必要があります。受け取ったら、保存して次のセクションを要求する必要があります。C# で記述された例は、コード プロジェクト ( http://www.codeproject.com/Tips/307548/Resume-Suppoert-Downloading ) で入手できます。

于 2013-02-15T16:39:41.713 に答える