从Contentpresenter获取ActualHeight/ActualWidth

Question

我得到了这段XAML代码，并尝试访问NaN的Contentpresenter的Width/Height。在那之后，我做了一些研究，发现我需要获取FrameworkElement.ActualWidth和FrameworkElement.ActualHeight，但我无法访问它们。它们的值为{{DependencyProperty.UnsetValue}}

下面是XAML (顺便说一下:它是一个自定义控件)：

   <local:MultiBindingConv
        x:Key="MultiBindingConv" />
   <Style TargetType="{x:Type local:CADViewer}">
        <Setter Property="Template">
            <Setter.Value>
            <ControlTemplate
                    TargetType="{x:Type local:CADViewer}">
               <ContentPresenter Name="CadContent" Content="{Binding VisualContainer, RelativeSource={RelativeSource TemplatedParent}}">
                  <i:Interaction.Triggers>
                     <i:EventTrigger
                                        EventName="SizeChanged">
                        <i:InvokeCommandAction
                                            Command="{Binding ContentSizeChanged, RelativeSource={RelativeSource TemplatedParent}}">
                           <i:InvokeCommandAction.CommandParameter>
                              <MultiBinding Converter="{StaticResource MultiBindingConv}">
                                 <Binding ElementName="CadContent" Path="FrameworkElement.ActualWidth"/>
                                 <Binding ElementName="CadContent" Path="FrameworkElement.ActualHeight"/>
                              </MultiBinding>
                           </i:InvokeCommandAction.CommandParameter>
                        </i:InvokeCommandAction>
                     </i:EventTrigger>
                  </i:Interaction.Triggers>
               </ContentPresenter>
               <!--<TextBlock Text="{Binding VisualContainer.ActualHeight, RelativeSource={RelativeSource TemplatedParent}}"/>-->
            </ControlTemplate>
         </Setter.Value>
        </Setter>
    </Style>