问从后台线程打开模式窗体以阻止UI线程，而不同时阻止后台线程

EN

Public Class Form1

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        If Not BackgroundWorker1.IsBusy Then
            BackgroundWorker1.RunWorkerAsync()
        End If
    End Sub

    Private Delegate Sub BlockingDelegate(ByVal reason As String)

    Private Sub StartBlockingTask(ByVal reason As String)
        If Me.InvokeRequired Then
            Dim del As New BlockingDelegate(AddressOf StartBlockingTask)
            Me.BeginInvoke(del, New Object() {reason})
        Else
            Try
                _frmBlock.lblBlock.Text = reason
                _frmBlock.ShowDialog()
            Catch ex As Exception
                'stuff
            End Try
        End If
    End Sub

    Private Sub EndBlockingTask()
        If Me.InvokeRequired Then
            Dim del As New BlockingDelegate(AddressOf EndBlockingTask)
            Me.BeginInvoke(del, New Object() {""})
        Else
            Try
                If (Not _frmBlock Is Nothing) Then
                    _frmBlock.DialogResult = Windows.Forms.DialogResult.OK
                End If
            Catch ex As Exception
                'stuff
            End Try
        End If
    End Sub

    Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        For i As Integer = 1 To 10
            BackgroundWorker1.ReportProgress(i)
            System.Threading.Thread.Sleep(1000)

            If i = 4 Then
                Dim del As New BlockingDelegate(AddressOf StartBlockingTask)
                del("bada...")
            ElseIf i = 7 Then
                Dim del As New BlockingDelegate(AddressOf EndBlockingTask)
                del("bing!")
            End If
        Next
    End Sub

    Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
        Label1.Text = e.ProgressPercentage
    End Sub

End Class

 Private Sub StartBlockingTask(ByVal reason As String)
    If Me.InvokeRequired Then
        Dim del As New BlockingDelegate(AddressOf StartBlockingTask)


   Private Sub EndBlockingTask()
        If Me.InvokeRequired Then
            Dim del As New BlockingDelegate(AddressOf EndBlockingTask)

Delegate Sub MySubDelegate(ByVal x As Integer)
Protected Sub Test()
   Dim c2 As New class2()
   ' Test the delegate.
   c2.DelegateTest()
End Sub

Class class1
   Sub Sub1(ByVal x As Integer)
      MessageBox.Show("The value of x is: " & CStr(x))
   End Sub
End Class

Class class2
   Sub DelegateTest()
      Dim c1 As Class1
      Dim msd As MySubDelegate
      c1 = New Class1()
      ' Create an instance of the delegate.
      msd = AddressOf c1.Sub1
      msd.Invoke(10) ' Call the method.
   End Sub
End Class