Custom Control Part 1

I've struggled to find a really simple example of creating a custom control. So I created a simple control that did only "one thing" then removed the "one thing" to leave just the very least plumbing that I could.

Starting with a new class that inherits from TextBox:

public class DemoTextBox : TextBox
{
   static DemoTextBox()
   {
      // Create a callback for when the TextProperty changes
      PropertyChangedCallback callback = new PropertyChangedCallback(TextPropertyChanged);
      // Override the TextProperty metadata in order to link up the callback routine
      TextProperty.OverrideMetadata(
         typeof(DemoTextBox),
         new FrameworkPropertyMetadata(callback));
   }
   static void TextPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
   {
      // Cast the Sender to an object of this class
      DemoTextBox textBox = (DemoTextBox)sender;

   }
}

Add a ResourceDictionary called Generic.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:DepProp>
   <Style TargetType="{x:Type local:DemoTextBox}">
      <Style.Triggers>
         <!-- create a trigger here -->
      </Style.Triggers>
   </Style>
</ResourceDictionary>

And a reference to the new control in the Window:

<Window x:Class="DepProp.Window2"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:DepProp"    
    Title="Window2" Height="300" Width="300">
   <Window.Resources>
      <ResourceDictionary Source="Generic.xaml"/>
   </Window.Resources>
   <StackPanel>
      <local:DemoTextBox x:Name="TextBoxV1" Text="Original Value" />
   </StackPanel>
</Window>