Question

I’m using a Threading.DispatcherTimer and every tick of the timer runs a subroutine.

Is it possible that if the subroutine takes longer then 1s for the processor to finish that it will mess up the time of the timer that is counting in seconds?

Try
  timercount = Nothing
  timercount = New DispatcherTimer()
  timercount.Interval = TimeSpan.FromSeconds(1)
  timercount.Start()
  AddHandler timercount.Tick, AddressOf TickMe 'Every Second the 'TickMe' Method runs
Catch ex As Exception
  '  MessageBox.Show(ex.Message)
End Try

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Private Sub TickMe()
  CL(0).Actual = H.Actual

  TextBoxSerialNumber.Focus()

  IntSec = IntSec + 1

  H.ActualBoxTime = H.ActualBoxTime.AddSeconds(1) 
  CL(0).ActualBoxTime = H.ActualBoxTime

  If IntSec Mod 60 = 0 Then
    H.Actual = H.Actual + 1
    CL(0).Actual = H.Actual
  End If

  CL(0).TargetBox = H.TargetBox

  PopulateCutGrid(CL)
End Sub

I’ve found after 50-60 minutes of counting it’s off by almost 10 minutes!

Answer 1

From the MSDN article regarding DispatchTimer:

Timers are not guaranteed to execute exactly when the time interval occurs, but they are guaranteed to not execute before the time interval occurs. This is because DispatcherTimer operations are placed on the Dispatcher queue like other operations. When the DispatcherTimer operation executes is dependent on the other jobs in the queue and their priorities.

If you need something more precise, I would recommend System.Threading.Timer. Each time the method of this timer is invoked, a ThreadPool thread is used. From this article:

The callback method executed by the timer should be reentrant, because it is called on ThreadPool threads. The callback can be executed simultaneously on two thread pool threads if the timer interval is less than the time required to execute the callback, or if all thread pool threads are in use and the callback is queued multiple times.

Also forgot to mention that you’ll need to use Invoke and InvokeRequired for WinForms or Dispatcher for WPF (I think, since I don’t use WPF).

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Edit 1:

Regarding your comment about needing total seconds, you can just store the original DateTime somewhere, and total seconds would be calculated using (DateTime.Now - StoredDateTime).TotalSeconds(). I would also recommend reading this article about threading in WPF to see if it applies in your case.

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Edit2:

Actually, since I think the only thing you’re after is a precise count of elapsed time, you could use a Stopwatch to keep track of time. Try using the regular DispatchTimer and just refer to the stopwatch each “tick” of that timer. That way, the Stopwatch is what keeps track of time, not the timer that could be used just for updating the UI.