vb.net – 进度条和后台工作者

发布时间：2020-12-17 07:16:27 所属栏目：百科来源：网络整理

导读：我在VB.Net中有一个进度条和后台工作程序,我希望以不同的形式工作,如下所示： Form1(){MaxRows = 10for i = 0 to MaxRows then// Update my value on the progressbar....next} ProgressBarForm Private Sub ProgressBarForm_Shown(sender As Object,e As Ev

我在VB.Net中有一个进度条和后台工作程序,我希望以不同的形式工作,如下所示：

Form1()
{
MaxRows = 10
for i = 0 to MaxRows then
// Update my value on the progressbar
....

next
}

ProgressBarForm

Private Sub ProgressBarForm_Shown(sender As Object,e As EventArgs) Handles Me.Shown
        TransferProgressBar.Visible = True
        ProgressBarBackgroundWorker.RunWorkerAsync()
    End Sub

    Private Sub ProgressBarBackgroundWorker_DoWork(sender As Object,e As ComponentModel.DoWorkEventArgs) Handles ProgressBarBackgroundWorker.DoWork
        For i = 0 To TransferProgressBar.Maximum
            'Dim Percentage As Integer = Math.Round(((i / (TransferProgressBar.Maximum - TransferProgressBar.Minimum)) * 100))
            ProgressBarBackgroundWorker.ReportProgress(i / 100)
        Next

    End Sub

    Private Sub ProgressBarBackgroundWorker_ProgressChanged(sender As Object,e As ComponentModel.ProgressChangedEventArgs) Handles ProgressBarBackgroundWorker.ProgressChanged
        TransferProgressBar.Value = e.ProgressPercentage
        PercentageLabel.Text = "Processing....." & TransferProgressBar.Value.ToString() & "%"
    End Sub

    Private Sub ProgressBarBackgroundWorker_RunWorkerCompleted(sender As Object,e As ComponentModel.RunWorkerCompletedEventArgs) Handles ProgressBarBackgroundWorker.RunWorkerCompleted
        MsgBox("Task Completed!")
        Me.Close()
    End Sub

如何使用其他表单/ Sub中的backgroundworker更新我的进度条值？请告诉我.我在这里有点困惑.

解决方法

你似乎把它带到了前面.而不是处理ProgressBar更新的BackgroundWorker,使用BGW来完成耗时的工作.然后,您可以定期使用内置的ReportProgress方法为ProgressBar / Form提供更新.

通常,您不能(直接)从其创建的线程(即UI线程)访问UI控件(如ProgressBar). ReportProgress事件在原始/ UI线程上引发,以使基本进度报告变得容易.

但是,它几乎仅限于此.要执行更多操作,例如将长进程的结果发布到ListBox,您可以使用Delegate更新其他/ UI线程上的控件.

具有长时间运行任务的表单

Private WithEvents bgw As New BackgroundWorker
Private frmProg As ProgForm          ' progress bar form

' start up
Private Sub Button1_Click(sender ...etc
    ' set up 
    bgw.WorkerReportsProgress = True
    bgw.WorkerSupportsCancellation = True

    If frmProg Is Nothing Then          ' make sure progress form is instanced
        ProgForm = New frmProg
    End If

    If bgw.IsBusy = False Then
        frmProg.Show()
        bgw.RunWorkerAsync(10)         ' do some important work x10
    End If

End Sub

' the job that will take a while
Private Sub bgw_DoWork(sender As Object,e As DoWorkEventArgs) 
                  Handles bgw.DoWork
    ' ToDo: with multiple workers use sender,not 'bgw'
    ' get the amount of work to do
    Dim numToDo As Integer = CInt(e.Argument)

    ' important,time consuming work done here
    For n As Integer = 1 To numToDo
        ' do the "work"
        System.Threading.Thread.Sleep(100)

        ' post a notice,passing the percentage (raises the ProgressChanged event)
        bgw.ReportProgress(Convert.ToInt32((n / numToDo) * 100)  
    Next
End Sub

' event raised from DoWork via ReportProgress
Private Sub bgw_ProgressChanged(sender As Object,e As ProgressChangedEventArgs) 
      Handles bgw.ProgressChanged
    ' method added on the Progress form to 

    ' receive percentage and update the meter:
    frmProg.UpdateProgress(e.ProgressPercentage)

    ' if the progress bar was on the same form,' update it directly:
    'MyProgBar.Value = MyProgBar.Maximum
    'MyProgBar.Value = pct
End Sub

' optional event raised when the long running task is complete
Private Sub bgw_RunWorkerCompleted(sender As Object,e As RunWorkerCompletedEventArgs) Handles bgw.RunWorkerCompleted

    ' when all done,report that too
    MessageBox.Show("Work Complete!")
End Sub

请注意,通常使用Thread.Sleep会冻结UI.这不会发生在这里,因为它是BackgroundWorker而不是放入睡眠的UI线程.

带进度条的表单：

Public Sub UpdateProgress(pct As Integer)

   ' ToDo: Add error checking 
    progress.Value = progress.Maximum
    progress.Value = pct
End Sub

（编辑：李大同）

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