CustomValidator

@inherits ControlComponent

<asp.Label @ref="this.message"
                                            Text="Enter an even number:"
                                            FontNames="Verdana"
                                            FontSize="10pt" />

<br />
<br />

<asp.TextBox ID="Text1" />

<asp.CustomValidator ControlToValidate="Text1"
                                            Display=" ValidatorDisplay.Static"
                                            ErrorMessage="Not an even number!"
                                            ForeColor="green"
                                            FontNames="verdana"
                                            FontSize="10pt"
                                            OnServerValidate="this.ServerValidation" />

<br />
<br />

<asp.Button Text="Validate"
                                            OnClick="this.ValidateBtn_OnClick" />

@code {
                                            private Label message;

                                            protected void ValidateBtn_OnClick(object sender, EventArgs e)
    {
                                            // Display whether the page passed validation.
                                            if (this.Page.IsValid)
        {
            message.Text = "Page is valid.";
        }
                                            else
        {
            message.Text = "Page is not valid!";
        }
    }

                                            protected void ServerValidation(object source, ServerValidateEventArgs args)
    {
                                            try
        {
                                            // Test whether the value entered into the text box is even.
                                            int i = int.Parse(args.Value);
            args.IsValid = ((i % 2) == 0);
        }
        catch
        {
            args.IsValid = false;
        }
    }
}