ControlTemplate中的ContentPresenter无法更改附加的依赖项属性 [英] ContentPresenter within ControlTemplate cannot change attached dependency property

问题描述

为什么下面的简化代码没有将TextBlock的字体大小设置为50?

Why does the following simplified code not sets the font-size of the TextBlock to 50?

<Window.Resources>
    <ControlTemplate TargetType="ContentControl" x:Key="Test">
        <ContentPresenter TextBlock.FontSize="50" />
    </ControlTemplate>        
</Window.Resources>        
<Grid>
    <ContentControl Template="{StaticResource Test}">
        <TextBlock>Test should be rendered big</TextBlock>
    </ContentControl>                   
</Grid>

如果更改FontSize属性的值，Visual Studio将以所需大小显示文本.编译或执行应用后，文本块的大小始终会重置为其默认大小.

If I change the value of the FontSize property, visual studio shows me the text in the size I want. After compiling or executing the app, the size of the textblock is always reset to its default size.

我还测试了具有样式和嵌入式资源的各种版本，但是我总是遇到无法从包含ContentPresenter的ControlTemplate中设置继承附加dp的情况.这是设计使然吗?

I have also tested various versions with styles and embedded resources but I end always in the situation that I cannot set inheriting attached dp's from within a ControlTemplate that contains a ContentPresenter. Is this by design?

推荐答案

我发现了这种现象的原因-这是设计使然:

I found the reason of this behavior - it’s by design:

如果ContentControl的内容已经是WPF元素，则在创建它之前先在ContenPresenter中使用它.元素的逻辑父级因此是 ContentControl .我可以通过将ContentControl-markup更改为以下内容来进行检查:

If the Content of ContentControl is already a WPF-Element, it is created before using it in the ContenPresenter. The logical parent of the element is therefore ContentControl. I can check this through changing the ContentControl-markup to the following:

<ContentControl Template="{StaticResource Test}" TextBlock.FontSize="50">                
    <TextBlock>
            This text now is shown with a size of 50
    </TextBlock>                    
</ContentControl>

在此示例中，文本大小为50.我也可以使用Visual Studio的wpf-visualizer证明这一论点.父级是ContentControl，通过dp继承，FontSize取自父级(ContentControl)，并且显示的文字大小为50！

In this example the text size is 50 as desired. I can prove this argumentation also with wpf-visualizer of visual studio. The parent is ContentControl and through dp-inheritance, the FontSize is taken from the parent (ContentControl), and the text is shown with a size of 50!

另一种行为:

<Window.Resources>
    <ControlTemplate x:Key="Test"  TargetType="{x:Type ContentControl}">
        <ContentPresenter  TextBlock.FontSize="50"/>
    </ControlTemplate>
</Window.Resources>                
<Grid>
    <ContentControl Template="{StaticResource Test}">                
        This text is shown with a size of 50
    </ContentControl>
</Grid>

在这种情况下，文本框是通过ContentPresenter 创建的，因为无法在可视树中输入文本.文本框没有父级，但是TemplateParent属性作为TextBoxes父级导致ContentPresenter，并且DP系统通过从ContentPresenter附加的依赖项属性继承获取FontSize-value.因此，在这种情况下，字体大小更改为50.

In this scenario, the TextBox is created through the ContentPresenter because text cannot be entered in the visual tree. The textbox has no parent but the TemplateParent-property leads to the ContentPresenter as the TextBoxes parent and the DP-system takes the FontSize-value through attached dependency property inheritance from the ContentPresenter. That’s why in this scenario the font size is changed to 50.

此处

我不明白的是，为什么VS2010在编译前会显示FontSize 50.

What I don’t understand is, why VS2010 shows the FontSize 50 before compiling.

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