TextBox uses the ExceptionValidationRule and UpdateSourceExceptionFilter handler : TextBox Validation « Windows Presentation Foundation « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. Windows Presentation Foundation
3. TextBox Validation

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:c="clr-namespace:WpfApplication1"
  x:Class="WpfApplication1.Window1">
    <Window.Resources>
        <c:MyDataSource x:Key="ods"/>
        <ControlTemplate x:Key="validationTemplate">
            <DockPanel>
                <TextBlock Foreground="Red" FontSize="20">!</TextBlock>
                <AdornedElementPlaceholder/>
            </DockPanel>
        </ControlTemplate>
        <Style x:Key="textBoxInError" TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip"
              Value="{Binding RelativeSource={x:Static RelativeSource.Self},Path=(Validation.Errors)[0].ErrorContent}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <StackPanel>
        <TextBox Name="textBox3" Width="50" FontSize="15"
             Validation.ErrorTemplate="{StaticResource validationTemplate}"
             Style="{StaticResource textBoxInError}">
            <TextBox.Text>
                <Binding Path="Age3" Source="{StaticResource ods}" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <ExceptionValidationRule/>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>

        <CheckBox Name="cb" Checked="UseCustomHandler" Unchecked="DisableCustomHandler">Enable Custom Handler (see ToolTip)</CheckBox>
    </StackPanel>
</Window>

//File:Window.xaml.cs
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Data;
using System.Globalization;
using System.Collections.ObjectModel;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        void UseCustomHandler(object sender, RoutedEventArgs e)
        {
            BindingExpression myBindingExpression = textBox3.GetBindingExpression(TextBox.TextProperty);
            Binding myBinding = myBindingExpression.ParentBinding;
            myBinding.UpdateSourceExceptionFilter = new UpdateSourceExceptionFilterCallback(ReturnExceptionHandler);
            myBindingExpression.UpdateSource();
        }

        void DisableCustomHandler(object sender, RoutedEventArgs e)
        {
            Binding myBinding = BindingOperations.GetBinding(textBox3, TextBox.TextProperty);
            myBinding.UpdateSourceExceptionFilter -= new UpdateSourceExceptionFilterCallback(ReturnExceptionHandler);
            BindingOperations.GetBindingExpression(textBox3, TextBox.TextProperty).UpdateSource();
        }

        object ReturnExceptionHandler(object bindingExpression, Exception exception)
        {
            return "This is from the UpdateSourceExceptionFilterCallBack.";
        }
    }
    public class AgeRangeRule : ValidationRule
    {
        private int _min;
        private int _max;

        public AgeRangeRule()
        {
        }

        public int Min
        {
            get { return _min; }
            set { _min = value; }
        }

        public int Max
        {
            get { return _max; }
            set { _max = value; }
        }

        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            int age = 0;

            try
            {
                if (((string)value).Length > 0)
                    age = Int32.Parse((String)value);
            }
            catch (Exception e)
            {
                return new ValidationResult(false, "Illegal characters or " + e.Message);
            }

            if ((age < Min) || (age > Max))
            {
                return new ValidationResult(false,
                  "Please enter an age in the range: " + Min + " - " + Max + ".");
            }
            else
            {
                return new ValidationResult(true, null);
            }
        }
    }

    public class MyDataSource
    {
        private int _age;
        private int _age2;
        private int _age3;

        public MyDataSource()
        {
            Age = 0;
            Age2 = 0;
        }

        public int Age
        {
            get { return _age; }
            set { _age = value; }
        }
        public int Age2
        {
            get { return _age2; }
            set { _age2 = value; }
        }

        public int Age3
        {
            get { return _age3; }
            set { _age3 = value; }
        }
    }
}

24.16.TextBox Validation
	24.16.1.	TextBox with custom ErrorTemplate and ToolTip
	24.16.2.	TextBox uses the ExceptionValidationRule and UpdateSourceExceptionFilter handler
	24.16.3.	TextBox with UpdateSourceExceptionFilter handler
	24.16.4.	TextBox with default ErrorTemplate