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Custom Event Arguments
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Introduction
Introduction

You've probably seen custom event arguments in use, probably in the DataGrid section of ASP.NET. Custom event arguments (from now on abbreviated to eventargs) allow you to create a class that you pass along with your events that contain extra information in them that you may want. The DataGridCommandEventArgs contains masses of information about the DataGrid and lets you manipulate it through it. Although I won't be showing you how to do that, this article will show you the basics of setting up some custom eventargs and implementing them.

What are they?

Just incase you are unsure what I'm taking about, custom eventargs are just a replacement (usually inherited from EventArgs) for the normal EventArgs on event handlers.

eg. Instead of -

Sub MyEventHandler(ByVal sender As Object, ByVal e As EventArgs)

You would use -

Sub MyEventHandler(ByVal sender As Object, ByVal e As CustomEventArgs)

Why use them?

If you check out my article on HTTPModules then you will see that I use them for sending the name of the browser to the event handler. If you have an event handler and you need to pass a lot of information (eg. Information about a user - Name, Address, Username, password, etc.) then this is the way.

The standard EventArgs can really only be passed in as EventArgs.Empty ie. empty. However, the class is there for you to be able to inherit from instead.

 

Creating the Arguments
Creating the Arguments

Here is a sample class which has inherited from EventArgs, it is the one in the HTTPModule article -

<Serializable()> Public Class BrowserEventArgs : Inherits EventArgs
Public
BrowserName As
String

Public Sub New(ByVal BrowserID As String)
BrowserName = BrowserID

End
Sub

End Class

Setting up and raising the event

Setting up the event and raising it

Now you need to create a Delegate for the event which will contain the custom event handler string.

Public Delegate Sub bdetEventHandler(ByVal sender As Object, ByVal e As BrowserEventArgs)
Public
Event bdet As
bdetEventHandler

The bdetEventHandler is the Delegate for bdet which basically means that the event bdet takes in two parameters - an object and  BrowserEventArgs object.

RaiseEvent bdet(Me, New BrowserEventArgs("Mozilla"))

The event hander will then have to look like -

Sub SampMod_bdet(ByVal sender As Object, ByVal e As BrowserEventArgs)
....

Summary

This article was just a quick tutorial of how to get up some custom event arguments. There is a lot more you can do with these than I showed you here (as you can probably imagine) and there will be more information on Delegates in the future.


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