...
<Intersoft:UXGridViewTextColumn Binding="{Binding FQDN, Mode=TwoWay, ValidatesOnExceptions=True,NotifyOnValidationError=True,ValidatesOnNotifyDataErrors=True}"/>
...

...
<Intersoft:FieldLabel Header="FQDN:">
    <Intersoft:UXTextBox Text="{Binding SelectedItem.FQDN, Mode=TwoWay}" Style="{StaticResource FieldLabelTextBoxStyle}"/>
</Intersoft:FieldLabel>
...

From the snippet code, changes that you made in “FQDN” UXTextBox will be updated on both the target (the UXTextBox itself) and the source (the SelectedItem property). In TwoWay bindings, changes to the target automatically update the source. Instead of updating through UXGridView, this action will directly update the changes on the source.

Silverlight/WPF supports simple data validation in TwoWay bindings for target-to-source updates. To receive notification that a validation error has occurred or has been resolved, you should set the NotifyOnValidationError property to true on the binding object. This tells the binding engine to raise the BindingValidationError event when a validation error is added to or removed from the Validation.Errors collection.

The following example shows how to provide custom binding validation using ValidatesOnExceptions.

View Model

using ClientUI.Samples.Models;
using System.ComponentModel;
using System;

namespace ClientUI.Samples.ViewModels
{
    public class MainPageViewModel : INotifyPropertyChanged
    {
        public MainPageViewModel()
        {

        }

        private double _value;

        public double Value
        {
            get { return this._value; }
            set
            {
                if (this._value != value)
                {
                    if (value < 0)
                        throw new Exception("Amount must be greater than zero.");

                    this._value = value;
                    this.OnPropertyChanged("Value");
                }
            }
        }

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }
}

View

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:Intersoft="http://intersoft.clientui.com/schemas"    
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"      
    xmlns:vm="clr-namespace:ClientUI.Samples.ViewModels"
    mc:Ignorable="d"
        x:Class="ClientUI.Samples.MainPage" Width="800" Height="600">
    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.DataContext>
            <vm:MainPageViewModel/>
        </Grid.DataContext>
        <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
            <Intersoft:UXTextBox Width="50" Margin="10">
                <Intersoft:UXTextBox.Text>
                    <Binding Mode="TwoWay" Path="Value" NotifyOnValidationError="true" ValidatesOnExceptions="true"/>
                </Intersoft:UXTextBox.Text>
            </Intersoft:UXTextBox>
            <Intersoft:UXButton Height="50" Width="150" Content="Click To Update Source"/>
        </StackPanel>
    </Grid>
</UserControl>

After the sample starts, type in letters instead of numbers to get an error caused by the type converter. Type in a negative number to get an error from the source object’s set accessor. Type in a positive number to resolve the validation error. UXTextBox target-to-source updates occurs only when the UXTextBox loses focus. The button is provided to change the focus.

Hope this helps.