Timer Constructor (TimerCallback, Object, Int32, Int32)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Initializes a new instance of the Timer class, using a 32-bit signed integer to specify the time interval.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
<SecuritySafeCriticalAttribute> _
Public Sub New ( _
    callback As TimerCallback, _
    state As Object, _
    dueTime As Integer, _
    period As Integer _
)

[SecuritySafeCriticalAttribute]
public Timer(
    TimerCallback callback,
    Object state,
    int dueTime,
    int period
)

Parameters

• callback
  Type: System.Threading.TimerCallback
  A delegate that represents a method to be executed.

• state
  Type: System.Object
  An object that contains information to be used by the callback method, or nulla null reference (Nothing in Visual Basic).

• dueTime
  Type: System.Int32
  The amount of time to delay before callback is invoked, in milliseconds. Specify Timeout.Infinite to prevent the timer from starting. Specify 0 (zero) to start the timer immediately.

• period
  Type: System.Int32
  The time interval between invocations of callback, in milliseconds. Specify Timeout.Infinite to disable periodic signaling.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	The dueTime or period parameter is negative and is not equal to Timeout.Infinite.
ArgumentNullException	The callback parameter is nulla null reference (Nothing in Visual Basic).

Remarks

The delegate specified by the callback parameter is invoked once after dueTime elapses, and thereafter each time the period time interval elapses.

Note:
Visual Basic users can omit the TimerCallback constructor, and simply use the AddressOf operator when specifying the callback method. Visual Basic automatically calls the correct delegate constructor.

If dueTime is 0 (zero), callback is invoked immediately. If dueTime is Timeout.Infinite, callback is not invoked; the timer is disabled but can be re-enabled by calling the Change method.

If period is 0 (zero) or Timeout.Infinite, and dueTime is not Timeout.Infinite, callback is invoked once; the periodic behavior of the timer is disabled but can be re-enabled using the Change method.

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

Examples

The following code example shows how to create a TimerCallback delegate and initialize a new instance of the Timer class. In this example, the delegate is created implicitly. Its type is inferred by the Visual Basic and C# compilers.

This example creates a timer, uses the Timer.Change method to change its interval, and then uses the Timer.Dispose method to destroy it.

The example displays its output in a TextBlock on the UI thread. To access the TextBlock from the callback thread, the example uses the Dispatcher property to obtain a Dispatcher object for the TextBlock, and then uses the Dispatcher.BeginInvoke method to make the cross-thread call.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Imports System.Threading

' The following Imports are not required for the timer. They merely simplify 
' the code.
Imports System.Windows.Controls
Imports System.Windows.Input

' The Example class holds a reference to the timer, and contains the 
' event handler for the MouseLeftButtonUp events that control the demo.
'
Public Class Example

   ' The Shared Demo method sets the starting message and creates an 
   ' instance of Example, which hooks up the handler for the MouseLeftButtonUp
   ' event.
   Public Shared Sub Demo(ByVal outputBlock As TextBlock)

      outputBlock.Text &= "Click to create the timer." & vbLf
      Dim dummy As New Example(outputBlock)

   End Sub


   ' Instance data for the demo.
   Private phase As Integer = 0
   Private t As Timer

   Public Sub New(ByVal outputBlock As TextBlock)

      ' Hook up the mouse event when a new Example object is created. Note
      ' that this keeps garbage collection from reclaiming the Example 
      ' object.
      AddHandler outputBlock.MouseLeftButtonUp, AddressOf Me.MouseUp

   End Sub

   Private Sub MouseUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs)

      Dim outputBlock As TextBlock = CType(sender, TextBlock)

      If phase = 0 Then
         ' On the first click, create the timer.
         outputBlock.Text &= vbLf & "Creating the timer at " & _
            DateTime.Now.ToString("h:mm:ss.fff") & _
            ", to start in 1 second with a half-second interval." & vbLf & _
            "Click to change the interval from 1/2 second to 1 second." & vbLf & vbLf

         ' Create a timer that invokes the callback method after one second 
         ' (1000 milliseconds) and every 1/2 second thereafter. The TextBlock
         ' that is used for output is passed as the state object. Visual Basic 
         ' infers the delegate type, as if you had typed the following:
         '     New TimerCallback(AddressOf MyTimerCallback)
         ' 
         t = New Timer(AddressOf MyTimerCallback, outputBlock, 1000, 500)

      ElseIf phase = 1 Then
         ' On the next click, change the timer interval to every second.
         outputBlock.Text &= vbLf & "Changing the interval to one second." & vbLf & _
            "Click to destroy the timer." & vbLf & vbLf

         t.Change(0, 1000)

      Else
         ' On the last click, destroy the timer and shut down the demo.
         outputBlock.Text &= vbLf & "Destroying the timer." & vbLf & _
            "Refresh the page to run the demo again."
         RemoveHandler outputBlock.MouseLeftButtonUp, AddressOf Me.MouseUp

         t.Dispose()

      End If

      phase += 1

   End Sub


   ' The shared callback method is invoked on a ThreadPool thread by the Timer. 
   ' The state object is passed to the callback method on each invocation. In this
   ' example, the state object is the TextBlock that displays output. In order to
   ' update the TextBlock object, which is on the UI thread, you must make the  
   ' cross-thread call by using the Dispatcher object that is associated with the 
   ' TextBlock.
   Private Shared Sub MyTimerCallback(ByVal state As Object)

      Dim outputBlock As TextBlock = CType(state, TextBlock)
      Dim msg As String = DateTime.Now.ToString("h:mm:ss.fff") & _
                          " MyTimerCallback was called." & vbLf

      outputBlock.Dispatcher.BeginInvoke(displayHelper, outputBlock, msg)

   End Sub

   ' The DisplayOutput helper method and its delegate, displayHelper, are used by
   ' the BeginInvoke method of the Dispatcher object.
   Private Shared displayHelper _
                    As New Action(Of TextBlock, String)(AddressOf DisplayOutput)
   Private Shared Sub DisplayOutput(ByVal tb As TextBlock, ByVal msg As String)
      tb.Text &= msg
   End Sub

End Class

' This example produces output similar to the following:
'
'Click to create the timer.
'
'Creating the timer at 3:17:36.980, to start in 1 second with a half-second interval.
'Click to change the interval from 1/2 second to 1 second.
'
'3:17:38.072 MyTimerCallback was called.
'3:17:38.586 MyTimerCallback was called.
'3:17:39.101 MyTimerCallback was called.
'3:17:39.580 MyTimerCallback was called.
'
'Changing the interval to one second.
'Click to destroy the timer.
'
'3:17:39.656 MyTimerCallback was called.
'3:17:40.689 MyTimerCallback was called.
'
'Destroying the timer.
'Refresh the page to run the demo again.

using System;
using System.Threading;

// The following Imports are not required for the timer. They merely simplify 
// the code.
using System.Windows.Controls;
using System.Windows.Input;

// The Example class holds a reference to the timer, and contains the 
// event handler for the MouseLeftButtonUp events that control the demo.
//
public class Example
{
   // The static Demo method sets the starting message and creates an 
   // instance of Example, which hooks up the handler for the MouseLeftButtonUp
   // event.
   public static void Demo(TextBlock outputBlock)
   {
      outputBlock.Text += "Click to create the timer.\n";
      Example dummy = new Example(outputBlock);
   }


   // Instance data for the demo.
   private int phase = 0;
   private Timer t;

   public Example(TextBlock outputBlock)
   {
      // Hook up the mouse event when a new Example object is created. Note
      // that this keeps garbage collection from reclaiming the Example 
      // object.
      outputBlock.MouseLeftButtonUp += new MouseButtonEventHandler(this.MouseUp);
   }

   private void MouseUp(object sender, MouseButtonEventArgs e)
   {
      TextBlock outputBlock = (TextBlock) sender;

      if (phase==0)
      {
         // On the first click, create the timer.
         outputBlock.Text += "\nCreating the timer at " + 
               DateTime.Now.ToString("h:mm:ss.fff") + 
               ", to start in 1 second with a half-second interval.\n" +
               "Click to change the interval from 1/2 second to 1 second.\n\n";

         // Create a timer that invokes the callback method after one second 
         // (1000 milliseconds) and every 1/2 second thereafter. The TextBlock
         // that is used for output is passed as the state object. C# infers the 
         // delegate type, as if you had typed the following:
         //     new TimerCallback(MyTimerCallback)
         // 
         t = new Timer(MyTimerCallback, outputBlock, 1000, 500);

      }
      else if (phase==1)
      {
         outputBlock.Text += "\nChanging the interval to one second.\n" +
                             "Click to destroy the timer.\n\n";
         t.Change(0, 1000);
      }
      else
      {
         // On the last click, destroy the timer and shut down the demo.
         outputBlock.Text += "\nDestroying the timer.\n" + 
                             "Refresh the page to run the demo again.";
         outputBlock.MouseLeftButtonUp -= new MouseButtonEventHandler(this.MouseUp);

         t.Dispose();
      }

      phase += 1;
   }


   // The static callback method is invoked on a ThreadPool thread by the Timer. 
   // The state object is passed to the callback method on each invocation. In this
   // example, the state object is the TextBlock that displays output. In order to
   // update the TextBlock object, which is on the UI thread, you must make the  
   // cross-thread call by using the Dispatcher object that is associated with the 
   // TextBlock.
   private static void MyTimerCallback(object state)
   {
      TextBlock outputBlock = (TextBlock) state;
      string msg = DateTime.Now.ToString("h:mm:ss.fff") + " MyTimerCallback was called.\n";

      outputBlock.Dispatcher.BeginInvoke(delegate () { outputBlock.Text += msg; });
   }
}

/* This example produces output similar to the following:

Click to create the timer.

Creating the timer at 3:40:17.712, to start in 1 second with a half-second interval.
Click to change the interval from 1/2 second to 1 second.

3:40:18.820 MyTimerCallback was called.
3:40:19.335 MyTimerCallback was called.
3:40:19.849 MyTimerCallback was called.

Changing the interval to one second.
Click to destroy the timer.

3:40:20.317 MyTimerCallback was called.
3:40:21.331 MyTimerCallback was called.

Destroying the timer.
Refresh the page to run the demo again.
 */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also

Reference

Timer Class

Timer Overload

System.Threading Namespace

Other Resources

Timers