.NET Framework Class Library
Timer..::.Elapsed Event

Occurs when the interval elapses.

Namespace:  System.Timers
Assembly:  System (in System.dll)
Syntax

Visual Basic (Declaration)
<TimersDescriptionAttribute("TimerIntervalElapsed")> _
Public Event Elapsed As ElapsedEventHandler
Visual Basic (Usage)
Dim instance As Timer
Dim handler As ElapsedEventHandler

AddHandler instance.Elapsed, handler
C#
[TimersDescriptionAttribute("TimerIntervalElapsed")]
public event ElapsedEventHandler Elapsed
Visual C++
[TimersDescriptionAttribute(L"TimerIntervalElapsed")]
public:
 event ElapsedEventHandler^ Elapsed {
    void add (ElapsedEventHandler^ value);
    void remove (ElapsedEventHandler^ value);
}
JScript
JScript does not support events.
Remarks

If Enabled is set to true and AutoReset is set to false, the Timer raises the Elapsed event only once, the first time the interval elapses.

If Interval is set after the Timer has started, the count is reset. For example, if you set the interval to 5 seconds and then set Enabled to true, the count starts at the time Enabled is set. If you reset the interval to 10 seconds when count is 3 seconds, the Elapsed event is raised for the first time 13 seconds after Enabled was set to true.

The Elapsed event is raised on a ThreadPool thread. If the processing of the Elapsed event lasts longer than Interval, the event might be raised again on another ThreadPool thread. Thus, the event handler should be reentrant.

NoteNote:

The event-handling method might run on one thread at the same time that another thread calls the Stop method or sets the Enabled property to false. This might result in the Elapsed event being raised after the timer is stopped. The example code for the Stop method shows one way to avoid this race condition.

In the .NET Framework version 2.0 and earlier, the Timer component catches and suppresses all exceptions thrown by event handlers for the Elapsed event. This behavior is subject to change in future releases of the .NET Framework.

Examples

The following code example sets up an event handler for the Timer..::.Elapsed event, creates a timer, and starts the timer. The event handler displays the SignalTime property each time it is raised.

Visual Basic
Imports System
Imports System.Timers

Public Class Timer1

    Private Shared aTimer As System.Timers.Timer

    Public Shared Sub Main()
        ' Normally, the timer is declared at the class level,
        ' so that it stays in scope as long as it is needed.
        ' If the timer is declared in a long-running method,  
        ' KeepAlive must be used to prevent the JIT compiler 
        ' from allowing aggressive garbage collection to occur 
        ' before the method ends. (See end of method.)
        'Dim aTimer As System.Timers.Timer

        ' Create a timer with a ten second interval.
        aTimer = New System.Timers.Timer(10000)

        ' Hook up the Elapsed event for the timer.
        AddHandler aTimer.Elapsed, AddressOf OnTimedEvent

        ' Set the Interval to 2 seconds (2000 milliseconds).
        aTimer.Interval = 2000
        aTimer.Enabled = True

        Console.WriteLine("Press the Enter key to exit the program.")
        Console.ReadLine()

        ' If the timer is declared in a long-running method, use
        ' KeepAlive to prevent garbage collection from occurring
        ' before the method ends.
        'GC.KeepAlive(aTimer)
    End Sub

    ' Specify what you want to happen when the Elapsed event is 
    ' raised.
    Private Shared Sub OnTimedEvent(source As Object, e As ElapsedEventArgs)
        Console.WriteLine("The Elapsed event was raised at {0}", e.SignalTime)
    End Sub
End Class

' This code example produces output similar to the following:
'
'Press the Enter key to exit the program.
'The Elapsed event was raised at 5/20/2007 8:42:27 PM
'The Elapsed event was raised at 5/20/2007 8:42:29 PM
'The Elapsed event was raised at 5/20/2007 8:42:31 PM
'...
C#
using System;
using System.Timers;

public class Timer1
{
    private static System.Timers.Timer aTimer;

    public static void Main()
    {
        // Normally, the timer is declared at the class level,
        // so that it stays in scope as long as it is needed.
        // If the timer is declared in a long-running method,  
        // KeepAlive must be used to prevent the JIT compiler 
        // from allowing aggressive garbage collection to occur 
        // before the method ends. (See end of method.)
        //System.Timers.Timer aTimer;

        // Create a timer with a ten second interval.
        aTimer = new System.Timers.Timer(10000);

        // Hook up the Elapsed event for the timer.
        aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);

        // Set the Interval to 2 seconds (2000 milliseconds).
        aTimer.Interval = 2000;
        aTimer.Enabled = true;

        Console.WriteLine("Press the Enter key to exit the program.");
        Console.ReadLine();

        // If the timer is declared in a long-running method, use
        // KeepAlive to prevent garbage collection from occurring
        // before the method ends.
        //GC.KeepAlive(aTimer);
    }

    // Specify what you want to happen when the Elapsed event is 
    // raised.
    private static void OnTimedEvent(object source, ElapsedEventArgs e)
    {
        Console.WriteLine("The Elapsed event was raised at {0}", e.SignalTime);
    }
}

/* This code example produces output similar to the following:

Press the Enter key to exit the program.
The Elapsed event was raised at 5/20/2007 8:42:27 PM
The Elapsed event was raised at 5/20/2007 8:42:29 PM
The Elapsed event was raised at 5/20/2007 8:42:31 PM
...
 */
Visual C++
#using <system.dll>

using namespace System;
using namespace System::Timers;

public ref class Timer1
{
private: 
   static System::Timers::Timer^ aTimer;

public:
   static void Demo()
   {
      // Normally, the timer is declared at the class level,
      // so that it stays in scope as long as it is needed.
      // If the timer is declared in a long-running method,  
      // KeepAlive must be used to prevent the JIT compiler 
      // from allowing aggressive garbage collection to occur 
      // before the method ends. (See end of method.)
      //System::Timers::Timer^ aTimer;

      // Create a new Timer with Interval set to 10 seconds.
      aTimer = gcnew System::Timers::Timer( 10000 );

      // Hook up the Elapsed event for the timer.
      aTimer->Elapsed += gcnew ElapsedEventHandler( Timer1::OnTimedEvent );

      // Set the Interval to 2 seconds (2000 milliseconds).
      aTimer->Interval = 2000;
      aTimer->Enabled = true;

      Console::WriteLine("Press the Enter key to exit the program.");
      Console::ReadLine();

      // If the timer is declared in a long-running method, use
      // KeepAlive to prevent garbage collection from occurring
      // before the method ends.
      //GC::KeepAlive(aTimer);
   }


private:
   // Specify what you want to happen when the Elapsed event is 
   // raised.
   static void OnTimedEvent( Object^ source, ElapsedEventArgs^ e )
   {
      Console::WriteLine( "The Elapsed event was raised at {0}", e->SignalTime );
   }

};

int main()
{
   Timer1::Demo();
}

/* This code example produces output similar to the following:

Press the Enter key to exit the program.
The Elapsed event was raised at 5/20/2007 8:42:27 PM
The Elapsed event was raised at 5/20/2007 8:42:29 PM
The Elapsed event was raised at 5/20/2007 8:42:31 PM
...
 */
Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
See Also

Reference

Elapsed
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