TextChangedEventArgs Class

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"    
  x:Class="SDKSample.DetectChangedTextExample"
  Title="DetectChangedText">
  <StackPanel>
    <TextBox
      Name="tbCountingChanges"    
      TextChanged="textChangedEventHandler"
      TextWrapping="Wrap">
      Here is the initial text in the textbox.  Each time the contents of this box is changed, a change counter will
      be incremented and displayed in the TextBox below.  Note that the TextChanged event is called when the TextBox
      control is initially populated with text, so the changes counter starts of at 1.
    </TextBox>
    <TextBox Name="tbCounterText">0</TextBox>

  </StackPanel>  
</Page>

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;

namespace SDKSample
{

    public partial class DetectChangedTextExample : Page
    {

        // This is a counter for the number of times the TextChanged fires
        // for the tbCountingChanges TextBox.
        private int uiChanges = 0;

        // Event handler for TextChanged Event.
        private void textChangedEventHandler(object sender, TextChangedEventArgs args)
        {

            uiChanges++;
            if (tbCounterText != null)
            {
                tbCounterText.Text = uiChanges.ToString();
            }

        }
    }
}