.NET Reference Guide

Thread Timers

Last updated Jan 1, 2004.

The System.Threading.Timer class implements a simple lightweight timer that uses callback functions and is served by threadpool threads. This type of timer is not a component like the other two. It also has fewer features. It has the benefit, though, of not going through the event system, but rather making direct callbacks. When you create the timer, you specify the callback method, the time to wait before the first time the callback is executed, and the amount of time (period) between calls. You can't change the callback method once the timer has been created, but you can change the period or turn the timer off by calling the Change method.

You can pass information to the timer callback by creating a status object and passing a reference to that object to the constructor. This object is then passed to the timer callback where it can be modified.

The code below shows how you can use this type of timer in a Windows Forms program.

C#

// create the timer's state object
class TimerState
{
  public int counter = 0;
  public System.Threading.Timer tmr = null;
  public bool enabled = false;
}

private TimerState ts = new TimerState();

private void timer3Callback(object state)
{
  TimerState s = (TimerState)state;
  s.counter++;
  ShowLabel(label5, s.counter.ToString());
}

private void btnThreadTimer_Click(object sender, System.EventArgs e)
{
  if (ts.enabled)
  {
    // disable the timer
    ts.enabled = false;
    ts.tmr.Change(System.Threading.Timeout.Infinite,
      System.Threading.Timeout.Infinite);
    btnThreadTimer.Text = "Start";
  }
  else
  {
    if (ts.tmr == null)
      // first time through, create the timer
      ts.tmr = new System.Threading.Timer(
        new TimerCallback(timer3Callback), 
        ts, 1000, 1000);
    else
      // enable the timer
      ts.tmr.Change(1000, 1000);
    ts.enabled = true;
    btnThreadTimer.Text = "Stop";
  }
}

Visual Basic

' create the timer's state object
Class TimerState
  Public counter As Integer = 0
  Public tmr As System.Threading.Timer = Nothing
  Public enabled As Boolean = False
End Class

Private ts As TimerState = New TimerState

Private Sub timer3Callback(ByVal state As Object)
  Dim s As TimerState = DirectCast(state, TimerState)
  s.counter = s.counter + 1
  ShowLabel(label5, s.counter.ToString())
End Sub

Private Sub btnThreadTimer_Click(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles btnThreadTimer.Click
  If ts.enabled Then
    ' disable the timer
    ts.enabled = False
    ts.tmr.Change(System.Threading.Timeout.Infinite, _
    System.Threading.Timeout.Infinite)
    btnThreadTimer.Text = "Start"
  Else
    If ts.tmr Is Nothing Then
      ' first time through, create the timer
      ts.tmr = New System.Threading.Timer( _
        New System.Threading.TimerCallback(AddressOf 
timer3Callback), _
        ts, 1000, 1000)

    Else
      ' enable the timer
      ts.tmr.Change(1000, 1000)
    End If
    ts.enabled = True
    btnThreadTimer.Text = "Stop"
  End If
End Sub

Although you could use a thread timer for this purpose, the System.Timer or Windows.Forms.Timer is probably more appropriate. The primary use for thread timers is within threads, or where you don't want the overhead of going through the events subsystem.