TextBox focus listener

   
  
<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:custom="clr-namespace:WpfApplication1"
    Title="Keyboard Sample" Height="250" Width="300">
    <StackPanel>
        <Label Name="lblNumberOfTargetHits" HorizontalAlignment="Center"/>
        <TextBox Name="txtTargetKey" GotKeyboardFocus="TextBoxGotKeyboardFocus" LostKeyboardFocus="TextBoxLostKeyboardFocus">A</TextBox>
        <TextBox TextWrapping="Wrap" GotKeyboardFocus="TextBoxGotKeyboardFocus" LostKeyboardFocus="TextBoxLostKeyboardFocus" KeyDown="SourceTextKeyDown"/>
    </StackPanel>

</Window>


//File:Window.xaml.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using System.Windows.Annotations;
using System.Windows.Input;
namespace WpfApplication1
{
    public partial class Window1 : Window
    {

        public Window1()
        {
            InitializeComponent();
        }

        private void TextBoxGotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
        {
            TextBox source = e.Source as TextBox;
            if (source != null)
            {
                source.Background = Brushes.LightBlue;
                source.Clear();
            }
        }
        private void TextBoxLostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
        {
            TextBox source = e.Source as TextBox;

            if (source != null)
            {
                source.Background = Brushes.White;
            }
        }
        private void SourceTextKeyDown(object sender, KeyEventArgs e)
        {
            KeyConverter converter = new KeyConverter();
            Key target = Key.None;

            if (txtTargetKey.Text.Length == 1)
            {
                target = (Key)converter.ConvertFromString(txtTargetKey.Text);
            }
        }
    }
}