Private WithEvents counterPanel As Panel
Private WithEvents timer As DispatcherTimer = New DispatcherTimer()
Private counter As Integer = 0

Private Sub PanelClick(ByVal sender As System.Object, _
    ByVal e As System.Windows.Input.MouseButtonEventArgs) _
    Handles counterPanel.MouseLeftButtonDown

    If timer.IsEnabled Then timer.Stop() Else timer.Start()

End Sub

Private Sub TimerClick(ByVal sender As System.Object, _
    ByVal e As EventArgs) Handles timer.Tick

    counter += 1
    counterPanel.Children.Clear()
    Dim t As New TextBlock
    t.Text = counter.ToString
    counterPanel.Children.Add(t)

End Sub

Private Sub TestDispatcherTimer(ByVal p As Panel)

    Me.counterPanel = p
    timer.Interval = New TimeSpan(0, 0, 1)
    timer.Start()

End Sub

private void TestDispatcherTimer(Panel counterPanel)
{
    DispatcherTimer timer = new DispatcherTimer();
    int counter = 0;

    counterPanel.MouseLeftButtonDown += 
        delegate(object s, MouseButtonEventArgs args) {
            if (timer.IsEnabled) timer.Stop(); else timer.Start(); 
        };

    timer.Tick += 
        delegate(object s, EventArgs args) {
            counterPanel.Children.Clear();
            counterPanel.Children.Add( new TextBlock { 
                Text = counter++.ToString() });
        };

    timer.Interval = new TimeSpan(0, 0, 1); // one second
    timer.Start();
}