An attached behavior for WPF's TextBox control that provides auto-completion suggestions from a given collection

1. Install the package via NuGet

   	PM> Install-Package WPFTextBoxAutoComplete
   

2. Add a reference to the library in your view

   	xmlns:behaviors="clr-namespace:WPFTextBoxAutoComplete;assembly=WPFTextBoxAutoComplete"

3. Create a textbox and bind the "AutoCompleteItemsSource" to a collection of IEnumerable<String>

   	<TextBox 
   		Width="250"
   		HorizontalAlignment="Center"
   		Text="{Binding TestText, UpdateSourceTrigger=PropertyChanged}" 
   		behaviors:AutoCompleteBehavior.AutoCompleteItemsSource="{Binding TestItems}" 
   	/>

4. (Optional) Set the "AutoCompleteStringComparison" property, which is of type StringComparison

   	<TextBox 
   		Width="250"
   		HorizontalAlignment="Center"
   		Text="{Binding TestText, UpdateSourceTrigger=PropertyChanged}" 
   		behaviors:AutoCompleteBehavior.AutoCompleteItemsSource="{Binding TestItems}" 
   		behaviors:AutoCompleteBehavior.AutoCompleteStringComparison="InvariantCultureIgnoreCase"
   	/>

Now, every time the "TestText" property of your datacontext is changed, WPFTextBoxAutoComplete will provide you with auto-completion suggestions. To accept a suggestion, just hit "enter".