VB.NET Timer Examples

Monitor processes with the Timer type, and the ElapsedEventArgs argument, from the System.Timers namespace.

Timer. This class lets us call a subroutine every several seconds. We must construct a Timer instance and then add handlers to it.

Using the ElapsedEventHandler, we can specify a subroutine to perform maintenance or update data. We call Start, and use ElapsedEventArgs and SignalTime.Sub

First example. Here we create a new Timer with its constructor—we specify an interval of 200 milliseconds. We use the AddHandler operator to set the Elapsed event.Event

And: We use the method TimerElapsed (you can name it whatever you like) to run when the interval is reached.

SignalTime: The ElapsedEventArgs gives us access to SignalTime, which is a DateTime. It is the time the Timer was fired.

VB.NET program that uses Timer Imports System.Timers Module Module1 Sub Main() Dim timer As Timer = New Timer(200) AddHandler timer.Elapsed, New ElapsedEventHandler(AddressOf TimerElapsed) timer.Start() ' Wait and run the timer. Console.Read() End Sub Sub TimerElapsed(ByVal sender As Object, ByVal e As ElapsedEventArgs) ' Write the SignalTime. Dim time As DateTime = e.SignalTime Console.WriteLine("TIME: " + time) End Sub End Module Output TIME: 4/3/2019 2:49:43 PM TIME: 4/3/2019 2:49:43 PM TIME: 4/3/2019 2:49:44 PM TIME: 4/3/2019 2:49:44 PM TIME: 4/3/2019 2:49:44 PM TIME: 4/3/2019 2:49:44 PM TIME: 4/3/2019 2:49:44 PM TIME: 4/3/2019 2:49:45 PM

Class example. This class has a Timer instance and a List instance. In the Start subroutine, we construct the Timer, specifying its interval as 3000 milliseconds (3 seconds).Shared

Next: We call the AddHandler operator to assign the Handler subroutine as the code that is executed every 3 seconds.

Finally: We set the Enabled property to True to start the Timer. It begins measuring time elapsed.

Start: To start the Timer, the Start() subroutine will have to be called during website startup.

GetOutput: The GetOutput() Function will show the DateTimes that were collected by the Timer.

Class that uses Timer type: VB.NET Imports Microsoft.VisualBasic Imports System.Timers Public Class TimerTest Shared _timer As Timer Shared _list As List(Of String) = New List(Of String) ''' <summary> ''' Start the timer. ''' </summary> Shared Sub Start() _timer = New Timer(3000) AddHandler _timer.Elapsed, New ElapsedEventHandler(AddressOf Handler) _timer.Enabled = True End Sub ''' <summary> ''' Get timer output. ''' </summary> Shared Function GetOutput() As String Return String.Join("<br>", _list) End Function ''' <summary> ''' Timer event handler. ''' </summary> Shared Sub Handler(ByVal sender As Object, ByVal e As ElapsedEventArgs) _list.Add(DateTime.Now.ToString()) End Sub End Class

ASP.NET example. First, we should add the Global.asax file. In the Application_Start handler, we call the TimerTest.Start subroutine that was declared in the class.

Then: In the Application_BeginRequest subroutine, we output the text of the List collected by the Timer.

Example Global.asax: VB.NET <%@ Application Language="VB" %> <script runat="server"> Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs) TimerTest.Start() End Sub Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs) Response.Write(TimerTest.GetOutput()) End Sub </script>

Notes, ASP.NET. When you first visit the website, the Timer is started. From this point on, the Timer will add a String to the List every 3 seconds.

Tip: Refresh the page occasionally and you will see the Timer is executing its Handler code.

Default.aspx: If you are starting with an empty ASP.NET website, you will want to add a Default.aspx page as well.

Info: Default.aspx will trigger the runtime to call the Application_Start and Application_BeginRequest handlers.

A summary. Timer is an excellent way to maintain the data or caches in a website. And because it is separate from request handling, it will not cause slowdowns for visitors.
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