Textbox validation

[arial]

Ok.. I need help again.

I have a text box in my web form, so I am trying to do is as soon as user enters anything in text box other than 1....9,0 I have to give them a message saying invalid input.

How can I check user input an give them a message?

Thank You,

[Plater]

On a webform you will need to have a javascript function that watches the onkeydown() (or similar) function.

[arial]

I have a asp.net webform using c#.

My textbox is:
<asp:textbox id="txtqanum" runat="server"> </asp:textbox>

this one does not have a property of keypress,onblur etc.

I was thinking to compare it so asci value but ,how can compare that value entered in textbox to asci value?

like asc(txtqanum.te xt)

help me on this.

Thank You,

[Plater]

This does not work:

<asp:textbox id="txtqanum" onkeydown="SomeJavaScriptFunction();" runat="server"></asp:textbox>

[arial]

I don't get Onkeydown event handler.

I got the javascript function but I don't know where to call it.

[Plater]

It won't show up in the autocomplete.
An alternative is in the backend code, find that textbox control and do an AddAttribute() (I think that's the right name) for something like:

txtqanum.AddAttribute("onkeydown","SomeJavaScriptFunction();");