我的窝

Typically a control is rendered for its own sake, and doesn’t reflect underlying data. For example, a Button wouldn’t be bound to a business object – it’s there purely so it can be clicked on. A ContentControl or ListBox, however, generally appear so that they can present data for the user.

A DataTemplate, therefore, is used to provide visual structure for underlying data, while a ControlTemplate has nothing to do with underlying data and simply provides visual layout for the control itself.

A ControlTemplate will generally only contain TemplateBinding expressions, binding back to the properties on the control itself, while a DataTemplate will contain standard Binding expressions, binding to the properties of its DataContext (the business/domain object or view model).

来源：这里

前提是当Style在一个界面上被多次使用（比如MenuItem的Style，如果ItemContainerStyle来设置，使用的是同一个Style，被用到多个menuItem的情况）

就会出现：Specified element is already the logical child of another element. Disconnect it first.

如果错误被吃掉了，界面上就会出现没有被用上Style的元素。

比如

<Style x:Key="m1" TargetType="{x:Type MenuItem}"? BasedOn="{StaticResource {x:Type MenuItem}}" >
?????????? <Setter? Property="Header">
???????????????? <Setter.Value>

??????????????????????? <TextBlock………>

?????????????????? </Setter.Value>
?????????? </Setter>

?????? </Style>

类似这篇文章里提到的现象。解决方案是用xhared = false. 见msdn的解释。

?

<Label x:Shared="false" x:Key="l" Content="{Binding}">
????? </Label>
????? <Style x:Key="m1" TargetType="{x:Type MenuItem}"? BasedOn="{StaticResource {x:Type MenuItem}}" >
????????? <Setter? Property="Header" Value="{StaticResource l}">??????????????
????????? </Setter>
????? </Style>