RE : Beginners Nightmare .... PLEASE help

I have just started learning the ins and outs of ASP.Net and am running Web Matrix while getting to grips with the formatting etc.

My problem is that any time i add a textbox webcontrol to a page, instead of displaying the actual textbox I get an 'Error Rendering Control' box stating that 'RegisterForEventValidation can only be called during Render()'!!!

I am at a loss as to why this is happening, which isn't just restricted to the textbox webcontrol but ALL the control's available except the Label & Literal webcontrols which seem to behave properly.

Could someone please please please provide some guidance for this newbie to ASP.Net in order that I can keep the current enthusiasm going to learn.

Thanks so much in advance

Re: RE : Beginners Nightmare .... PLEASE help

Could you post your code, will be easier to debug

Re: RE : Beginners Nightmare .... PLEASE help

Hi,

Can you provide some of you code so I can take a look at it.

Re: RE : Beginners Nightmare .... PLEASE help

Hi the code is pasted below, VERY simple piece of code to place the current date & time into a textbox webcontrol.

The error originates on the actual webcontrol object when i place it in design view from the toolbox.

<%@ Page Language="VB" %>
<script runat="server">

    Sub Page_Load(sender as Object, e as EventArgs)
        currentDT.Value = DateTime.Now
    End Sub

</script>
<html>
<head>
</head>
<body>
    <form runat="server">
        <asp:TextBox id="currentDT" runat="server"></asp:TextBox>
        
    </form>
</body>
</html>

The compilation error points to line 5 of the code and states ---> "Compiler Error Message: BC30456: 'Value' is not a member of 'System.Web.UI.WebControls.TextBox'."

Re: RE : Beginners Nightmare .... PLEASE help

If you want to get a value to the textbox you are not able to do it in the page_load event. You can set the time in the Page_PreRender event. It is the exact same as the page_load syntax you just put Page_PreRender. It happens after the page_load event. In the Page_load event the textbox does not exist yet.

Re: RE : Beginners Nightmare .... PLEASE help

change:

currentDT.Value = DateTime.Now

currentDT.Text = DateTime.Now

Re: RE : Beginners Nightmare .... PLEASE help

Also just looking at it. You are using Textbox.Value = It should be Textbox.Text. And to convert the time to a string use the Convert.ToString method. This is a c# method. I don't use visual basic and never have so I don't know the syntax for it. But you may have to cast you time to a string I don't know for sure with visual basic. If you are learning you may want to think of learning c#. Alot of programmers have to learn c# a couple of years after visual as it is a better language with more features.

Re: RE : Beginners Nightmare .... PLEASE help

Hi seamus1982,

Wrong on booth things, the controls are available on page load, and c# and vb have the same features, main difference is syntax. However it's good to learn both as they are both used widely across industries. <:o:p>

Re: RE : Beginners Nightmare .... PLEASE help

Thanks guys, the changing the property to Text instead of Value worked but my (other) main issue is in the web matrix design screen when I try to add a web control fro the toolbox. When I place the textbox on the design pane I get the following :

"Error Rendering Control - currentDT An unhandled exception has occured. RegisterForEventValidation can only be called during Render()"

As a newbie to this it might be a minor annoyance to others but I was expecting an actual text box to be displayed.

Any explanation/help on this would be greatly appreciated.

Thanks again for helping me out with the code :)

Re: RE : Beginners Nightmare .... PLEASE help

Right if you want to correct me. The textbox is created in the pageload event. So if you want to insert data into the textbox programmatically in the page_load event this often causes errors. i.e the error message with this can only be done in the render event.

Secondly there are more features with c#. ie. operator overloading, alot more error catching features and there are more. I don't get why someone would correct me if they don't know for certain.

Re: RE : Beginners Nightmare .... PLEASE help

MasterToad

Thanks guys, the changing the property to Text instead of Value worked but my (other) main issue is in the web matrix design screen when I try to add a web control fro the toolbox. When I place the textbox on the design pane I get the following :

"Error Rendering Control - currentDT An unhandled exception has occured. RegisterForEventValidation can only be called during Render()"

As a newbie to this it might be a minor annoyance to others but I was expecting an actual text box to be displayed.

Any explanation/help on this would be greatly appreciated.

Thanks again for helping me out with the code :)

Hi,

If you put the code in your page_load event into the Page_PreRender event. That should work. So you just copy your code in the page_load event and put it into a different event. The Page_PreRender event or thhe Page_PreRenderComplete event. Everything should work properly then.

Re: RE : Beginners Nightmare .... PLEASE help

What development tool are you using?

Re: RE : Beginners Nightmare .... PLEASE help

ASP.Net Web Matrix, as I said the main issue i have with this is NOT the coding itself but the actual display of a toolbox object in the design screen not being displayed but instead an error_message being given. The only two objects that appear on the desing screen properly are the Label & Literal objects, all other objects produce the same error message (as mentioned earlier).

On running the code everything works (and looks) fine.

Re: RE : Beginners Nightmare .... PLEASE help

Do you not have the ability to use web developer express?

I've never used Webmatrix as a developer tool and what you are describing sounds like a bug in webmatrix. Poss worth another post in a different forum/category.

Re: RE : Beginners Nightmare .... PLEASE help

Are the objects that are not showing the objects that you are creating the input dynamically. Try creating the page without programmatically entering data into them. Then they should show up. If you want to programmatically put data into the do it in the page_prerender event rather than the page_load event. Have you tried putting the code into the page_prerender event? More than likely this is the issue.

Re: RE : Beginners Nightmare .... PLEASE help

MasterToad
ASP.Net Web Matrix

I agree with cookie_powered. I recommend that you stop using Web Matrix for Web Forms development, especially as you are just learning. If you like Web Forms, and feel comfortable dragging controls onto a design surface etc, use Visual Studio 2010 Express (which is free).

WebMatrix is a beta product that has been designed primarily to provide a different development paradigm - Web Pages. It works best with the Razor syntax and vbhtml or cshtml pages. It has bugs which will be addressed in the next beta, which will also have bugs no doubt, but for a beginner, I would recommend it.

http://www.mikesdotnetting.com/Article/145/Introducing-WebMatrix-An-Easier-Way-To-Do-ASP.NET
http://www.mikesdotnetting.com/Article/146/WebMatrix-A-First-Application

Re: RE : Beginners Nightmare .... PLEASE help

Not sure MasterToad is using WebMatrix or Visual Web Developer.

You mention adding things to a design view, but that only exists in Visual Web Developer or Visual Studio.

If you're looking at something like this:

http://www.microsoft.com/express/s/img/VWD2010Start.png

Then you're in Visual Web Developer. Not sure why that error message would appear when you drag a text box onto the design view, though...