Open or show a new instance of a form from a new thread in VB.NET

Question

I am trying to open or show a new instance of a form from a new thread in VB.NET.

Here is some code that I have come up with:

Thread starting procedure:

    Public Sub StartBellScheduleRun()
        Dim BS(NumClocks) As Threading.Thread
        For A As Integer = 0 To NumClocks - 1
            BS(A) = New Threading.Thread(AddressOf RunBellSchedule)
            BS(A).Start(A)
        Next
    End Sub

Procedure in new thread:

    Public Sub RunBellSchedule(ClockIndex As Integer)
        Do While Exiting = False
            If BellScheduleActive = True Then
                If EEMCAlertTime(ClockIndex).ToLongTimeString = WorkingEventBellTimes(EEMCEventIndex(ClockIndex)).EventTime.ToLongTimeString And BellRinging = False Then
                    EventName = CurrentEventBellTimes(EEMCEventIndex(ClockIndex)).EventName
                    EventMessage = CurrentEventBellTimes(EEMCEventIndex(ClockIndex)).EventMessage
                    CurrentEventTime = WorkingEventBellTimes(EEMCEventIndex(ClockIndex)).EventTime
                    Dim CurrentBellIngingForm As New BellRingingForm
                    If BellRingingForm.InvokeRequired Then
                        ' Dim asyncResult = BellRingingForm.BeginInvoke(New Action(AddressOf RunBellSchedule))
                        Dim d As New RunBellScheduleCallBack(AddressOf RunBellSchedule)
                        Invoke(d, New Object() {ClockIndex})
                    Else
                        CurrentBellIngingForm.Show()
                        'frmModal.ShowDialog(frmMain)
                    End If
                    '   If ScreenSetting >= 1 And ScreenSetting <= Screen.AllScreens.Count - 1 Then ShowNextEventSreen()
                End If
            End If
            Threading.Thread.Sleep(TimeUpdateRestingTime)
        Loop
    End Sub

This this the correct approach ore method?

Answer 1

Try to replace the Dim and If with this fragment:

Invoke(Sub()
         Dim CurrentBellIngingForm As New BellRingingForm
         CurrentBellIngingForm.Show()
       End Sub)

Answer 2

Hi @Marc Menzel ,

In WinForms, you cannot directly create or interact with UI controls like forms from a thread other than the main UI thread. Therefore, invoking the creation and display of the form on the UI thread is necessary.

                Dim CurrentBellIngingForm As New BellRingingForm()

                If frmMain.InvokeRequired Then
                    frmMain.Invoke(New Action(Sub() CurrentBellIngingForm.Show()))
                Else
                    CurrentBellIngingForm.Show()
                End If

Best Regards.

Jiachen Li

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