获取 FTP 服务器上的文件大小并将其放在标签上

Question

我正在尝试获取托管在 FTP 服务器上的文件的大小，并在 `BackgroundWorker 在后台工作时将其放入 Label。

我正在使用“Try”来获取值，但是在第一次尝试时就捕获了该值。下载后，如果我再次尝试获取它就可以了。

注意: 进度条在第一次尝试时也不起作用。

图片

我试过的：

Private Sub BWorkerD_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BWorkerD.DoWork

    Dim buffer(1023) As Byte
    Dim bytesIn As Integer
    Dim totalBytesIn As Integer
    Dim output As IO.Stream
    Dim flLength As Integer

    ''TRY TO GET FILE SIZE''

    Try
        Dim FTPRequest As FtpWebRequest = DirectCast(WebRequest.Create(txtFilePathD.Text), FtpWebRequest)
        FTPRequest.Credentials = New NetworkCredential(txtFTPUsernameD.Text, txtFTPPasswordD.Text)
        FTPRequest.Method = Net.WebRequestMethods.Ftp.GetFileSize

        flLength = CInt(FTPRequest.GetResponse.ContentLength)
        lblFileSizeD.Text = flLength & " bytes"

    Catch ex As Exception

    End Try

    Try
        Dim FTPRequest As FtpWebRequest = DirectCast(WebRequest.Create(txtFilePathD.Text), FtpWebRequest)
        FTPRequest.Credentials = New NetworkCredential(txtFTPUsernameD.Text, txtFTPPasswordD.Text)
        FTPRequest.Method = WebRequestMethods.Ftp.DownloadFile
        Dim stream As IO.Stream = FTPRequest.GetResponse.GetResponseStream
        Dim OutputFilePath As String = txtSavePathD.Text & "\" & IO.Path.GetFileName(txtFilePathD.Text)
        output = IO.File.Create(OutputFilePath)
        bytesIn = 1

        Do Until bytesIn < 1
            bytesIn = stream.Read(buffer, 0, 1024)
            If bytesIn > 0 Then
                output.Write(buffer, 0, bytesIn)
                totalBytesIn += bytesIn
                lblDownloadedBytesD.Text = totalBytesIn.ToString & " bytes"
                If flLength > 0 Then
                    Dim perc As Integer = (totalBytesIn / flLength) * 100
                    BWorkerD.ReportProgress(perc)
                End If
            End If
        Loop

        output.Close()
        stream.Close()

    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try
End Sub

''UPDATE EVERY PROGRESS - DONT WORK ON FIRST TRY''

Private Sub BWorkerD_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BWorkerD.ProgressChanged

    pBarD.Value = e.ProgressPercentage
    lblPercentD.Text = e.ProgressPercentage & " %"
End Sub

Answer 1

主要问题（设置Option Strict On以查找更多）：
您无法从不同于 UI 线程的线程访问 UI 对象。

您收到的错误是：

Cross-thread operation not valid:
Control lblFileSizeD accessed from a thread other than the thread it was created on

然后，lblDownloadedBytesD同样的错误。

此外，您正在使用空处理程序处理错误消息：

Catch ex As Exception

End Try

这会使任何处理无效，因为有 none。您只是让代码运行通过它而不采取任何操作。处理程序在那里，嗯，处理错误，而不是让它们不受检查。

当您需要访问和更新某些 UI 组件属性时，请使用 BackGroundWorker ReportProgress() method. This method has an overload that accepts a parameter of type Object. Meaning, you can feed it anything. This Object will be the e.UserState property in the ReportProgress ProgressChangedEventArgs class.

.RunWorkerAsync() method also accepts an Object parameter. This Object will become the e.Argument property of the BackgroundWorker.DoWork 事件。这为您实际传递给 BackGroundWorker.

的参数提供了一些灵活性

还有一个问题：Ftp下载程序不支持取消。运行时，用户无法停止。

最后一个问题：正如文档中所报告的，您永远不应在其 DoWork 事件中引用您在 UI 线程（表单）中实例化的 BackGroundWorker 对象。使用 sender 对象并将其转换为 BackGroundWorker class.

在此示例中，所有 UI 引用都委托给一个 Class 对象，该对象通过 RunWorkerAsync(Object) 方法（使用 e.Argument 属性).
Class 对象使用进度详细信息进行更新，然后馈送到 ReportProgress(Int32, Object) 方法，该方法运行在原始同步上下文中（UI 线程，其中 RunWorkerAsync 方法被调用）。
UI 可以安全更新。不能发生跨线程操作。

还实现了取消方法。这允许中止下载过程并删除部分下载的文件（如果已创建）。

错误处理很少，但这是您需要与自己的工具集成的部分。

（我为 UI 控件使用了相同的名称，应该更容易测试。）

Imports System.ComponentModel
Imports System.Globalization
Imports System.IO
Imports System.Net
Imports System.Net.Security
Imports System.Security.Cryptography.X509Certificates

Public Class frmBGWorkerDownload

    Friend WithEvents BWorkerD As BackgroundWorker
    Public Sub New()
        InitializeComponent()
        BWorkerD = New BackgroundWorker()
        BWorkerD.WorkerReportsProgress = True
        BWorkerD.WorkerSupportsCancellation = True

        AddHandler BWorkerD.DoWork, AddressOf BWorkerD_DoWork
        AddHandler BWorkerD.ProgressChanged, AddressOf BWorkerD_ProgressChanged
        AddHandler BWorkerD.RunWorkerCompleted, AddressOf BWorkerD_RunWorkerCompleted
        BWorkerD.RunWorkerAsync(BGWorkerObj)
    End Sub

    Private Class BGWorkerObject
        Public Property UserName As String
        Public Property Password As String
        Public Property ResourceURI As String
        Public Property FilePath As String
        Public Property FileLength As Long
        Public Property DownloadedBytes As Long
        Public Property BytesToDownload As Long
    End Class

    Private Sub btnDownload_Click(sender As Object, e As EventArgs) Handles btnDownload.Click
        pBarD.Value = 0
        Dim BGWorkerObj As BGWorkerObject = New BGWorkerObject With {
            .ResourceURI = txtFilePathD.Text,
            .FilePath = Path.Combine(txtSavePathD.Text, Path.GetFileName(txtFilePathD.Text)),
            .UserName = txtFTPUsernameD.Text,
            .Password = txtFTPPasswordD.Text
        }
    End Sub

    Private Sub BWorkerD_DoWork(sender As Object, e As DoWorkEventArgs)
        Dim BGW As BackgroundWorker = TryCast(sender, BackgroundWorker)
        Dim BGWorkerObj As BGWorkerObject = TryCast(e.Argument, BGWorkerObject)
        Dim FTPRequest As FtpWebRequest
        Dim BufferSize As Integer = 131072

        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 Or SecurityProtocolType.Tls12
        ServicePointManager.ServerCertificateValidationCallback =
            Function(snd As Object, Cert As X509Certificate, Chain As X509Chain, Err As SslPolicyErrors)
                Return True
            End Function

        FTPRequest = DirectCast(WebRequest.Create(BGWorkerObj.ResourceURI), FtpWebRequest)
        FTPRequest.Credentials = New NetworkCredential(BGWorkerObj.UserName, BGWorkerObj.Password)
        'FTPRequest.Method = WebRequestMethods.Ftp.GetFileSize
        '----------------------- UPDATE  ------------------------
        FTPRequest.Method = WebRequestMethods.Ftp.ListDirectoryDetails
        '--------------------- END UPDATE  ------------------------
        FTPRequest.EnableSsl = True

        '----------------------- UPDATE  ------------------------
        Using FtpResponse As WebResponse = FTPRequest.GetResponse, 
          DirListStream As Stream = FtpResponse.GetResponseStream(), 
          listReader As StreamReader = New StreamReader(DirListStream)
            While Not listReader.EndOfStream
                Dim DirContent As String = listReader.ReadLine()
                If DirContent.Contains(Path.GetFileNameWithoutExtension(BGWorkerObj.ResourceURI)) Then
                    BGWorkerObj.FileLength = Convert.ToInt64(DirContent.Split(New String() {" "}, StringSplitOptions.RemoveEmptyEntries)(4))
                    BGW.ReportProgress(0, BGWorkerObj)
                    Exit While
                End If
            End While
        End Using
        '----------------------- END UPDATE  ------------------------

        'Using FtpResponse As WebResponse = FTPRequest.GetResponse
        '    BGWorkerObj.FileLength = Convert.ToInt64(FtpResponse.ContentLength)
        '    BGW.ReportProgress(0, BGWorkerObj)
        'End Using

        If BGW.CancellationPending Then e.Cancel = True

        Try
            FTPRequest = CType(WebRequest.Create(BGWorkerObj.ResourceURI), FtpWebRequest)
            FTPRequest.EnableSsl = True
            FTPRequest.Credentials = New NetworkCredential(BGWorkerObj.UserName, BGWorkerObj.Password)
            FTPRequest.Method = WebRequestMethods.Ftp.DownloadFile

            Using Response As FtpWebResponse = DirectCast(FTPRequest.GetResponse, FtpWebResponse)
                If Response.StatusCode > 299 Then
                    e.Result = 0
                    Throw New Exception("The Ftp Server rejected the request. StatusCode: " &
                                        Response.StatusCode.ToString(),
                                        New InvalidOperationException(Response.StatusCode.ToString()))
                    Exit Sub
                End If
                Using stream = Response.GetResponseStream(), 
                  fileStream As FileStream = File.Create(BGWorkerObj.FilePath)
                    Dim read As Integer
                    Dim buffer As Byte() = New Byte(BufferSize - 1) {}
                    Do
                        read = stream.Read(buffer, 0, buffer.Length)
                        fileStream.Write(buffer, 0, read)
                        BGWorkerObj.DownloadedBytes += read
                        BGWorkerObj.BytesToDownload = BGWorkerObj.FileLength - BGWorkerObj.DownloadedBytes

                        If BGW.CancellationPending Then
                            e.Cancel = True
                            Exit Do
                        Else
                            BGW.ReportProgress(CInt((CSng(BGWorkerObj.DownloadedBytes) / BGWorkerObj.FileLength) * 100), BGWorkerObj)
                        End If
                    Loop While read > 0
                End Using
            End Using

        Catch ex As Exception
            If e.Cancel = False Then Throw
        Finally
            If e.Cancel = True Then
                If File.Exists(BGWorkerObj.FilePath) Then
                    File.Delete(BGWorkerObj.FilePath)
                End If
            End If
        End Try

    End Sub

    Private Sub BWorkerD_ProgressChanged(sender As Object, e As ProgressChangedEventArgs)
         pBarD.Value = e.ProgressPercentage
        lblPercentD.Text = e.ProgressPercentage.ToString() & " %"

        If lblFileSizeD.Text.Length = 0 Then
            lblFileSizeD.Text = CType(e.UserState, BGWorkerObject).FileLength.ToString("N0", CultureInfo.CurrentUICulture.NumberFormat)
        End If
        lblDownloadedBytesD.Text = CType(e.UserState, BGWorkerObject).DownloadedBytes.ToString("N0", CultureInfo.CurrentUICulture.NumberFormat)
        If e.ProgressPercentage <= 15 Then
            lblDownloadedBytesD.ForeColor = Color.Red
        ElseIf e.ProgressPercentage <= 66 Then
            lblDownloadedBytesD.ForeColor = Color.Orange
        Else
            lblDownloadedBytesD.ForeColor = Color.LightGreen
        End If
    End Sub

    Private Sub BWorkerD_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)
        Dim DownloadAborted As Boolean = False
        If e.Error IsNot Nothing Then
            DownloadAborted = True
            lblDownloadedBytesD.ForeColor = Color.Red
            lblDownloadedBytesD.Text = "Error!"
        ElseIf e.Cancelled Then
            DownloadAborted = True
            lblDownloadedBytesD.ForeColor = Color.Yellow
            lblDownloadedBytesD.Text = "Cancelled!"
            pBarD.Value = 0
            lblPercentD.Text = "0%"
        Else
            lblDownloadedBytesD.ForeColor = Color.LightGreen
            lblDownloadedBytesD.Text = "Download completed"
        End If
    End Sub

    Private Sub btnAbortDownload_Click(sender As Object, e As EventArgs) Handles btnAbortDownload.Click
        BWorkerD.CancelAsync()
    End Sub
End Class

描述的操作的可视化结果：

A PasteBin of the Form's Designer + Code

获取 FTP 服务器上的文件大小并将其放在标签上

Get File Size on FTP Server and put it on a Label

vb.net

winforms

ftp

progress-bar

backgroundworker