What do I need Protected WithEvents for?

I've noticed "Protected WithEvents" in the declarations for my controls on an ASPX web form. What's this all about? What does it mean?
When working with web forms, you need to have Protected WithEvents preceding the controls. Well almost. Here's what each one means and does.

Protected: You have to have this. This is what establishes the link between the instance of the control that is declared in the HTML and the instance in the code-behind.

HTML Markup (mypage.aspx):
<asp:button id="cmdClickMe" runat="server" />
Code-behind (mypage.aspx.vb):
Protected WithEvents cmdClickMe As System.Web.UI.WebControls.Button

WithEvents: This is not always required. This is used to provide the linkup of the event handlers so that you can create a method and use Handles cmdClickMe.Click to wire in the event. If you have a control on a web form that does not require events (which is more likely than not for things like labels or text boxes) you can remove the WithEvents keyword. Usually, the things that need event wiring are buttons, radio buttons, checkboxes, selects (dropdownlist or listbox), etc. If you want to use a text box's OnChanged event, then you would need it.

Optimization

If you have a lot of controls on a page, it would probably be a little faster if you don't have WithEvents on controls that don't need it. On a page by page basis, you probably wouldn't notice it but once the application is being used my many users at the same time, things will be faster.

Where to Next?

Wonder where to go next? You can read existing comments below or you can post a comment yourself on this article .


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On Sunday, May 07, 2006 10:26:35 AM george said:
nice article mate - short, concise and well explained....keep up the good work
On Monday, September 25, 2006 3:20:31 PM Tim Day said:
Nice job on this article.  Thanks very much for a clear explanation.
On Wednesday, June 11, 2008 6:01:05 PM Tod Conover said:
I've been using VB.NET for some years, and always place a "protected withevents" statement for each control.  In fact, I have a code generator that does all this for me.  Except, just today I have an instance of a page that is giving compiler errors implying I've already declared these controls.  If I remove the statements the page works fine.  Whoa! Something is obviously messed up and I expect to find it, but of the hundreds of web pages I've coded over the last several years, this is a first.  This page is a clone (copy/paste job) of another page.  I'm wondering if there is something sticky hidden somewhere related to the first instance of the page.  If you can explain how a page can work without "protected withevents" I would be interested.  
On Wednesday, June 11, 2008 9:30:14 PM Imar Spaanjaars said:
Hi Tod,

Did you update the class name to refer to the name page, rather than to the one you copied from? Looks like you are still referring to controls in the old page.

Imar
On Tuesday, September 09, 2008 1:19:47 PM Omair said:
Great article. Such basic yet concise explanation. Exactly what I was looking for. Thank you sir.
On Tuesday, September 22, 2009 9:09:50 PM DotNetNewbie said:
Thank you very much . This is neat and precise ..to the point thx.
On Wednesday, October 21, 2009 2:13:44 AM E said:
how about if my datagrid is dynamic? i have imagebutton on the datagrid and when it is clicked, it will chnage to another image? i try datagridcommandeventargs but it points to nothing
On Thursday, October 22, 2009 9:46:07 PM Imar Spaanjaars said:
Hi there,

Not sure if I understand what you're asking. Can you elaborate?

Imar
On Wednesday, April 27, 2011 10:25:02 AM subhransu said:
I am using .net 1.1. For each control I have to write he "Protected withevent Contolid as system.web.ui.controltype".

If u have  code generator for the control . Pls send to me  or send the link to down load the generator.

On Wednesday, April 27, 2011 10:29:07 AM Imar Spaanjaars said:
Hi there,

Visual Studio 2010 or the free VWD 2010 edition are probably the best "code generators" ;-)

But I guess you didn't want that as an answer....

Doesn't VS 2003 add those for you in Design View?

Cheers,

Imar

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