WPF

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;

namespace LeanQualityTool
{
    public class ValidatedTextBox : TextBox, INotifyPropertyChanged, IDataErrorInfo
    {
        private string _TextContents = "";

        public string TextContents
        {
            get { return _TextContents; }
            set { _TextContents = value;
                  NotifyPropertyChanged("TextContents");
                }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }

        #region IDataErrorInfo Members

        public string Error
        {
            get { return null; }
        }

        public string this[string fieldName]
        {
            get
            {
                string result = null;

                #region For Validating Text
                if (fieldName.Contains("Title"))
                {
                    if (this._TextContents.Length == 0)
                    {
                        result = "Text should not be blank";
                        throw new ArgumentException(result);
                    }
                    else
                    {
                        // Do searches for illegal chars in here if you like
                    }
                }
                #endregion

                return result;
            }

        #endregion
        }
    }
}

xmlns:vip="clr-namespace:LeanQualityTool"

                <vip:ValidatedTextBox Height="23" x:Name="txtJobTitle" HorizontalAlignment="Left" Width="276"
                     Style="{StaticResource validatedTextBox}">
                         <TextBox.Text>
                              <Binding Path="SelectedItem.Title" UpdateSourceTrigger="PropertyChanged"
                                       ValidatesOnDataErrors="True">
                              </Binding>
                         </TextBox.Text>
                </vip:ValidatedTextBox>