Timer Constructor (TimerCallback, Object, TimeSpan, TimeSpan)

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.TimeSpan
  The amount of time to delay before callback is invoked. Specify -1 (negative one) milliseconds to prevent the timer from starting. Specify 0 (zero) to start the timer immediately.

• period
  Type: System.TimeSpan
  The time interval between invocations of callback. Specify -1 (negative one) milliseconds to disable periodic signaling.

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

Public Class Example

   ' The Shared Demo method sets the starting message and hooks up the handler
   ' for the MouseLeftButtonUp event, which controls the demo.
   Public Shared Sub Demo(ByVal outputBlock As TextBlock)

      outputBlock.Text &= "Click to create the timer." & vbLf
      Example.outputBlock = outputBlock
      AddHandler outputBlock.MouseLeftButtonUp, AddressOf MouseUp

   End Sub

   ' Data for the demo.
   Private Shared phase As Integer = 0
   Private Shared t As Timer
   Private Shared outputBlock As TextBlock

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

      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 
         ' and every 1/2 second (500 milliseconds) thereafter. Visual Basic 
         ' infers the delegate type, as if you had typed the following:
         '     New TimerCallback(AddressOf MyTimerCallback)
         ' 
         t = New Timer(AddressOf MyTimerCallback, Nothing, _
                       New TimeSpan(0, 0, 1), New TimeSpan(0, 0, 0, 0, 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(New TimeSpan(0), New TimeSpan(0, 0, 1))

      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 MouseUp

         t.Dispose()

      End If

      phase += 1

   End Sub

   ' The shared callback method is invoked on a ThreadPool thread by the Timer. In 
   ' this example, the state object is not used. 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 msg As String = DateTime.Now.ToString("h:mm:ss.fff") & _
                          " MyTimerCallback was called." & vbLf

      outputBlock.Dispatcher.BeginInvoke(displayHelper, 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 String)(AddressOf DisplayOutput)
   Private Shared Sub DisplayOutput(ByVal msg As String)
      outputBlock.Text &= msg
   End Sub

End Class

' This example produces output similar to the following:
'
'Click to create the timer.
'
'Creating the timer at 4:14:48.114, to start in 1 second with a half-second interval.
'Click to change the interval from 1/2 second to 1 second.
'
'4:14:49.221 MyTimerCallback was called.
'4:14:49.736 MyTimerCallback was called.
'4:14:50.211 MyTimerCallback was called.
'
'Changing the interval to one second.
'Click to destroy the timer.
'
'4:14:50.640 MyTimerCallback was called.
'4:14:51.676 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;

public class Example
{
   // The static Demo method sets the starting message and hooks up the handler
   // for the MouseLeftButtonUp event, which controls the demo.
   public static void Demo(TextBlock outputBlock)
   {
      outputBlock.Text += "Click to create the timer.\n";
      Example.outputBlock = outputBlock;
      outputBlock.MouseLeftButtonUp += new MouseButtonEventHandler(MouseUp);
   }

   // Data for the demo.
   private static int phase = 0;
   private static Timer t;
   private static TextBlock outputBlock;

   private static void MouseUp(object sender, MouseButtonEventArgs e)
   {
      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, 
                       new TimeSpan(0, 0, 1), new TimeSpan(0, 0, 0, 0, 500));

      }
      else if (phase==1)
      {
         outputBlock.Text += "\nChanging the interval to one second.\n" +
                             "Click to destroy the timer.\n\n";
         t.Change(new TimeSpan(0), new TimeSpan(0, 0, 1));
      }
      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(MouseUp);

         t.Dispose();
      }

      phase += 1;
   }

   // The static callback method is invoked on a ThreadPool thread by the Timer. In 
   // this example, the state object is not used. 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 4:27:38.623, to start in 1 second with a half-second interval.
Click to change the interval from 1/2 second to 1 second.

4:27:39.731 MyTimerCallback was called.
4:27:40.245 MyTimerCallback was called.
4:27:40.719 MyTimerCallback was called.

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

4:27:40.895 MyTimerCallback was called.
4:27:41.945 MyTimerCallback was called.

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