A DispatcherTimer will run only when the app is running, not when it is suspended. You can set it up with an Interval to control how often it should call its Tick delegate. Here's a code snippet to call the TimerTick function approximately every second:
Dim timer As New DispatcherTimer()
timer.Interval = TimeSpan.FromSeconds(1)
AddHandler timer.Tick, AddressOf TimerTick
timer.Start()
For test purposes, TimerTick will update a counter and tell us how many times it has been called:
Private Sub TimerTick(sender As Object, e As Object)
numTicks = numTicks + 1
outputField.Text = numTicks
End Sub
--Rob