private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            string type = "";

            if (type == "ConstPayoff")
            {
                UserControl ctrl = new ConstantPayoffCtrl();
                ctrl.DataContext = new ConstantPayoffCtrlViewModel();
                this.PayoffDetailCtrl_.Children.Add(ctrl);
            }
        }
        private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            string type = "";

            if (type == "ConstPayoff") 
            {
                UserControl ctrl = new ConstantPayoffCtrl();
                ctrl.DataContext = new ConstantPayoffCtrlViewModel();
                this.PayoffDetailCtrl_.Children.Add(ctrl);
            }
        }