#142 – Dependency Property Value Sources: #8 – Theme Style Triggers

The eighth source in the list of sources for the base value of a dependency property is a theme style trigger.  A theme style trigger is a trigger defined in the default style for a control.  Every control that ships with WPF has a default style that dictates its appearance, also known as a theme style.

As an example, notice that when you set the IsEditable property of a ComboBox to true, it’s appearance changes.

IsEditable false:  

IsEditable true:  

The change in appearance is caused by a trigger in the default style.  If you right-click on a ComboBox in Blend and pick Edit a Template | Edit a Copy, you can see the default style for a ComboBox, including the following trigger on IsEditable.

				<Trigger Property="IsEditable" Value="true">
					<Setter Property="BorderBrush" Value="{StaticResource TextBoxBorder}"/>
					<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
					<Setter Property="IsTabStop" Value="false"/>
					<Setter Property="Padding" Value="3"/>
					<Setter Property="Template" Value="{StaticResource ComboBoxEditableTemplate}"/>
				</Trigger>