Interpolate value into ErrorMessage in asp:Validator

Question

A web form "form.aspx" contains an asp:TextBox field "Former_occupation", with a maximum length of 175 characters. The following asp:Validator performs a length check thereon :

<asp:RegularExpressionValidator
ID="CheckOccupationLength"
ControlToValidate="Former_occupation"
runat="server"
ValidationExpression="^[\s\S]{0,175}$"
Text="175 characters max"
ErrorMessage = "'Former Occupation' must be no more than 175 characters"
EnableClientScript="False"
/>

How can I amend it to report the actual number of characters, as in (e.g.,) ""'Former Occupation' must be no more than 175 characters (currently 183)" ? In case relevant, the form starts as follows :

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Form.aspx.cs" Inherits="SendMail" ResponseEncoding="utf-8" %>

Answer 1

No that is not possible with that control. You could always set the MaxLength on the textbox to 175

https://learn.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.textbox.maxlength?view=netframework-4.8

Answer 2

Consider creating a custom server-side validator. Check a simple example:

public class MyValidator : BaseValidator
{
    protected override bool EvaluateIsValid( )
    {
        var tb = (TextBox)Page.FindControl( ControlToValidate );
        string text = tb.Text;

        if( text.Length <= 10 )
        {
            ErrorMessage = $"The length must be greater than 10. Current length: {text.Length}";
            return false;
        }
        else
        {
            return true;
        }
    }
}

After compilation it should appear in Toolbox. You can drag it to your form. It will look like this:

<tag1:MyValidator ID="MyValidator1" runat="server" EnableClientScript="false" ControlToValidate="Former_occupation"/>

Enhance it according to your needs.

Answer 3

Hi @Philip Taylor (Hellenic Institute) ,
I suggest you could use jquery. Just like this:

Best regards,
Yijing Sun

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