public ActionResult DisplayFormEvent(EventViewModel model)
        {
            // If everything is valid, then set ModelStateIsValid = true; so javaScript will redirect to Index() action which will populate this newly created event inside of calendar.
            // else if something has failed, Add error message
            // In both cases redirect to partial view.

            if (model != null && ModelState.IsValid)
            {
                if (model.End.HasValue && model.Start.HasValue && DateTime.Compare(model.Start.Value, model.End.Value) <= 0)
                {
                    if (string.IsNullOrEmpty(model.Id))
                    {
                        // Add new event.
                        eventsCategoryList.Add
                            (new CategoryItemViewModel()
                        {
                            Id = new Random().Next(20, 1000).ToString(),
                            EventDescription = new ContentViewModel().AddText(model.Description),
                            Title            = model.Title,
                            Start            = model.Start,
                            End    = model.End,
                            AllDay = model.AllDay
                        }
                            );
                    }
                    else
                    {
                        // Edit existing event.

                        var eventToUpdate = GetAppointment(model.Id);
                        if (eventToUpdate != null)
                        {
                            eventToUpdate = model.ToCategoryItemViewModel(eventToUpdate);
                            eventsCategoryList.Remove(eventToUpdate);
                            eventsCategoryList.Add(eventToUpdate);
                        }
                    }
                    model.ModelStateIsValid = true;
                }
                else
                {
                    AddErrorMessage("End", "End Session must occur later than Start Session.");
                }
            }
            else if (model == null)
            {
                AddErrorMessage("Model is null.");
                return(Content(string.Empty));
            }
            return(PartialView("EditorTemplates/Object", model));
        }