Question

A few weeks ago I wrote a wrapper for the ServiceController control to enhance and streamline the base ServiceController. One of the changes I made was to add a monitoring component using the System.Threading.Timer object. On any change of status, an event is raised to the parent class. The actual monitoring works fine, but when the event is handled in the main form, my program abruptly ends – no exceptions, no warning, it just quits. Here’s a skeleton version of the control:

Public Class EnhancedServiceController
    Inherits ServiceController

    Public Event Stopped(ByVal sender As Object, ByVal e As System.EventArgs)
    Public Event Started(ByVal sender As Object, ByVal e As System.EventArgs)

    Private _LastStatus As System.ServiceProcess.ServiceControllerStatus

    Private serviceCheckTimer as System.Threading.Timer
    Private serviceCheckTimerDelegate as System.Threading.TimerCallback

    ...

    Private Sub StartMonitor()
        MyBase.Refresh()
        _LastStatus = MyBase.Status
        serviceCheckTimerDelegate = New System.Threading.TimerCallback(AddressOf CheckStatus)
        serviceCheckTimer = New System.Threading.Timer(serviceCheckTimerDelegate, Nothing, 0, 60*1000)
    End Sub

    Private Sub CheckStatus()
        MyBase.Refresh()
        Dim s As Integer = MyBase.Status
        Select Case s
            Case ServiceControllerStatus.Stopped
                If Not s = _LastStatus Then
                    RaiseEvent Stopped(Me, New System.EventArgs)
                End If
            Case ServiceControllerStatus.Running
                If Not s = _LastStatus Then
                    RaiseEvent Started(Me, New System.EventArgs)
                End If
        End Select
        _LastStatus = s
    End Sub

End Class

And the form:

Public Class Form1
    Private Sub ServiceStarted(ByVal sender As Object, ByVal e As System.EventArgs) Handles ESC.Started
        Me.TextBox1.Text = "STARTED"
    End Sub

    Private Sub ServiceStopped(ByVal sender As Object, ByVal e As System.EventArgs) Handles ESC.Stopped
        Me.TextBox1.Text = "STOPPED"
    End Sub
End Class

If I had to guess, I’d say that there’s some sort of thread problem, but I’m not sure how to handle that in the form. Any ideas?

Answer 1

IF it is a threading issue then you are probably trying to update the UI from a non-UI thread.

So something like this should solve that…

Private Delegate Sub UpdateTextBoxDelegate(byval tText as String)

Private Sub UpdateTextBox(byval tText As String)
    If Me.InvokeRequired Then
        Me.Invoke(New UpdateTextBoxDelegate(AddressOf UpdateTextBox), tText)
        Exit Sub
    End If

    TextBox1.Text = tText
End Sub

Private Sub ServiceStarted(ByVal sender As Object, ByVal e As System.EventArgs) Handles ESC.Started 
    UpdateTextBox ("STARTED")
End Sub 

Private Sub ServiceStopped(ByVal sender As Object, ByVal e As System.EventArgs) Handles ESC.Stopped
    UpdateTextBox("STOPPED")
End Sub