Timer.Change Method (Int32, Int32)

Changes the start time and the interval between method invocations for a timer, using 32-bit signed integers to measure time intervals.

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

public bool Change(
	int dueTime,
	int period


Type: System.Int32
The amount of time to delay before the invoking the callback method that was specified when the Timer was constructed, in milliseconds. Specify Timeout.Infinite to prevent the timer from restarting. Specify 0 (zero) to restart the timer immediately.
Type: System.Int32
The time interval between invocations of the callback method that was specified when the Timer was constructed, in milliseconds. Specify Timeout.Infinite to disable periodic signaling.

Return Value

Type: System.Boolean
true if the timer was successfully updated; otherwise, false.


The Timer has already been disposed.


The dueTime or period parameter is negative and is not equal to Timeout.Infinite.

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

If dueTime is 0 (zero), the callback method is invoked immediately. If dueTime is Timeout.Infinite, the callback method is never invoked; the timer is disabled but can be re-enabled by calling Change and specifying a positive value for dueTime.

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

The following example demonstrates how to start a Timer and, after a set number of invocations, change its period.

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.

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);
         // 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);


      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.


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

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

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