winforms 获取FTP服务器上的文件大小并将其放在标签上

我试图获取托管在FTP服务器上的文件的大小，并将其放在Label中，而`BackgroundWorker在后台工作。
我使用“Try”来获取值，但是在第一次尝试时就捕获了该值。下载后，如果我按下尝试再次获得它，那么它的工作。

注意：第一次尝试时，进度条也不工作。
图片

我尝试过的：

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

主要问题（设置Option Strict On以查找更多）：
您不能从UI Thread以外的线程访问UI对象。
您收到的错误是：
跨线程操作无效：
控件lblFileSizeD从创建该控件的线程以外的线程访问
然后，lblDownloadedBytesD也会出现同样的错误。
此外，你正在使用一个空的处理程序来吃掉你的错误消息：

Catch ex As Exception

End Try

这使任何 * 处理 * 无效，因为没有任何处理。你只是让代码在不采取任何行动的情况下运行它。处理程序是用来处理错误的，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BackGroundWorkerReportProgress()方法。此方法有一个接受Object类型参数的重载。意思是，你可以喂它任何东西。此Object将是ReportProgressProgressChangedEventArgs类中的e.UserState属性。
.RunWorkerAsync()方法也接受Object参数。此Object将成为BackgroundWorker.DoWork事件的e.Argument属性。这为您实际传递给BackGroundWorker的参数提供了一定的灵活性。
还有一个问题FTP下载过程不支持取消。当运行时，用户无法停止它。
最后一个问题：正如文档中所报告的那样，您永远不应该在其DoWork事件中引用您在UI线程（Form）中示例化的BackGroundWorker对象。使用sender对象并将其转换为BackGroundWorker类。
在此示例中，所有UI引用都委托给通过RunWorkerAsync(Object)方法（使用e.Argument属性）传递给DoWork事件的Class对象。
Class对象使用进度详细信息进行更新，然后提供给ReportProgress(Int32, Object)方法，该方法在原始同步上下文（UI线程，在其中调用RunWorkerAsync方法）中运行。
可以安全地更新UI。不能发生跨线程操作。
还实现了一种消除方法。这允许中止下载过程并删除部分下载的文件（如果已创建）。
错误处理是最小的，但这是您需要与自己的工具集成的东西。
（我已经为UI控件使用了相同的名称，它应该更容易测试。

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

        ' Windows 7 / Windows 10 lacking maintenance    
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12

        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

操作的视觉结果描述：

A PasteBin of the Form's Designer + Code

winforms 获取FTP服务器上的文件大小并将其放在标签上

1条答案

相关问题

热门标签

最新问答