ServerSideValidator.ascx.cs

using System;
using CMS.FormEngine.Web.UI;
using CMS.Helpers;
// ReSharper disable ArrangeAccessorOwnerBody

namespace CMSApp.CMSFormControls.Custom
{
    public partial class ServerSideValidator : FormEngineUserControl
    {
        public override object Value
        {
            get { return txtValue.Value; }
            set { txtValue.Value = ValidationHelper.GetString(value, string.Empty); }
        }

        protected override void OnInit(EventArgs e)
        {
            Form.SubmitButton.Click += SubmitButtonOnClick;
            base.OnInit(e);
        }

        private void SubmitButtonOnClick(object sender, EventArgs e)
        {
            var valid = CustomValidationHelper.ServerSideValidationMethod(Value);

            if (!valid)
            {
                //TODO: Invalidate the form before save or notify. (Form.?)
            }
        }
    }
}