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Posted 28 May 2008

A Basic Scheduler

, 28 May 2008
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Define schedules to the program for executing programmer defined jobs


I needed a simple scheduler to execute on an exact time / time span for generating automated reports. I checked various articles and the Internet for a scheduler that could tick off exactly as required and if it failed, then at the nearest next time.


While searching the Internet, I found an article by Andy Brummer which provided me with quite a few ideas to go about the code, but I needed something much more simpler, so it did not solve my purpose. Moreover, I was programming in VB.NET and the supplied codes were in C#, which on the whole would make it difficult for me to implement.

Before we continue any further, it would be a great help if you could read about delegates, calling and storing. I would suggest that you read a good article by Abhishek Khanna on delegates. It is a very important addition in VB.NET and simplifies many issues.

I would also suggest that you go through the Microsoft Library - MSDN about delegates, it's a very resourceful guide for quite a few programming issues.


The entire code block is wrapped within a class named Scheduler. It is dependant on three objects, namely:

  1. System.Windows.Forms.Timer
  2. System.Collections.ArrayList
  3. System.Data.DataTable

The DataTable is used for storing all events happening in the duration. This is done so as to allow immediate changes in the values. I had tried using ArrayList and other collection objects, but I did not get proper results doing so.

SetSchedule.Columns.Add(New DataColumn("SchType", System.Type.GetType("System.String")))
SetSchedule.Columns.Add(New DataColumn
    ("exeTime", System.Type.GetType("System.DateTime")))
SetSchedule.Columns.Add(New DataColumn("active", System.Type.GetType("System.Boolean")))
SetSchedule.Columns.Add(New DataColumn
    ("NextexeTime", System.Type.GetType("System.DateTime")))
SetSchedule.Columns.Add(New DataColumn
    ("TimeDiff", System.Type.GetType("System.TimeSpan")))

I added these five fields to the DataTable for keeping a track of the schedule, and I enumerated the following:

Public Enum Scheduled
    Once = 1
    BySecond = 2
    ByMinute = 4
    ByHour = 8
    Daily = 16
    Weekly = 32
    Monthly = 64
    Yearly = 128
    Regular = 256
End Enum

I used an ArrayList to store all events to execute on the scheduler match.

Using the Code

Add the class project to your solution and take a reference to it in your project.

Declare a variable as follows:

Dim sch As New Scheduler.Scheduler

Declare and allocate your delegates to functions and Subs:

'Declare a Delegate without Parameters
Delegate Sub ShowMessage()
'Declare a Delegate With Parameters
Delegate Sub ShowMessageBox(ByVal str As String)

'Define a Sub/Function without Parameters
Private Sub DisplayMessage()
    RichTextBox1.Text += "It is time: " + Now.ToString + vbCrLf
End Sub

'Define a Sub/Function with Parameters
Private Sub DisplayMessageBox(ByVal str As String)
    MsgBox("It is time: " + Now.ToString)
End Sub

'Pass a Delegate without Parameters
Dim msd As ShowMessage = AddressOf DisplayMessage

'Pass a Delegate with Parameters
Dim msd1 As ShowMessageBox = AddressOf DisplayMessageBox

Set the scheduler timers:

'Add a Schedule to Do the Events On a Particular Date/Time
'Add a Schedule to do the Events, after every Time Span
sch.AddSchedule(New TimeSpan(0, 5, 0))
'Add a Schedule to do the Events, after every Time Span starting from Date/Time
sch.AddSchedule(#5/28/2008 4:00:00 AM#, New TimeSpan(0, 5, 0))
'Add a Schedule to do the Events, EveryDay at the Said Times in 24Hrs Clock
sch.AddSchedule("09:25", "21:25")

Declare the events:

sch.AddEvent(msd1, "Test String")

Start the scheduler:



  • 28th May, 2008: First release

Contact Me

In case you have any problems with the code, you can contact me at or on my IM (Instant Messenger)


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Didara F Dosabhai
Database Developer Wizard Enterprise Pvt Ltd
India India
Database Developer

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Comments and Discussions

QuestionMessage Closed Pin
12-May-14 9:06
memberSai Pranad12-May-14 9:06 
QuestionA couple more examples? Pin
beckerben10-Oct-08 17:57
memberbeckerben10-Oct-08 17:57 
Generalin practice use whats built in to windows or linux Pin
Leblanc Meneses2-Jun-08 8:35
memberLeblanc Meneses2-Jun-08 8:35 
GeneralRe: in practice use whats built in to windows or linux Pin
Noctris24-Jul-08 6:20
memberNoctris24-Jul-08 6:20 
GeneralRe: in practice use whats built in to windows or linux Pin
Leblanc Meneses24-Jul-08 8:30
memberLeblanc Meneses24-Jul-08 8:30 
GeneralRe: in practice use whats built in to windows or linux Pin
Noctris8-Oct-08 0:27
memberNoctris8-Oct-08 0:27 
GeneralRe: in practice use whats built in to windows or linux Pin
Leblanc Meneses8-Oct-08 10:10
memberLeblanc Meneses8-Oct-08 10:10 
GeneralDatabase enabled.... Pin
Stewart Roberts30-May-08 7:14
memberStewart Roberts30-May-08 7:14 
GeneralNice work Pin
dnpro30-May-08 3:34
memberdnpro30-May-08 3:34 
GeneralLets state the obvious [modified] Pin
Programm3r28-May-08 19:50
member Programm3r 28-May-08 19:50 
GeneralTypo in title Pin
leppie28-May-08 6:49
member leppie 28-May-08 6:49 

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