您可以在scrollbar示例控件模板中看到它是如何完成的
http://msdn.microsoft.com/en-us/library/ms742173.aspx
简而言之,资源字典中有两个模板:
<ControlTemplate x:Key="VerticalScrollBar" TargetType="{x:Type ScrollBar}"> ...
<ControlTemplate x:Key="HorizontalScrollBar" TargetType="{x:Type ScrollBar}"> ...
<Style x:Key="{x:Type ScrollBar}" TargetType="{x:Type ScrollBar}">
<Style.Triggers>
<Trigger Property="Orientation" Value="Horizontal">
<Setter Property="Template" Value="{StaticResource HorizontalScrollBar}" />
</Trigger>
<Trigger Property="Orientation" Value="Vertical">
<Setter Property="Template" Value="{StaticResource VerticalScrollBar}" />
</Trigger>
</Style.Triggers>
</Style>