wpf - このカスタム エキスパンダーをハードコードされていない高さにするにはどうすればよいですか?

Question

カスタム エキスパンダーのコードをダウンロードし、1 つの例外を除いて、希望どおりに変更しました。Height は、展開時に 100 にハードコードされています。これは、通常のエキスパンダーのように機能し、コントロール内にあるものに合わせて高さを設定する必要があります。これに関連する XAML を次に示します。Value="100" が表示されます。Auto を試しましたが、現在のように double 値を入力する必要があります。何か案は？

<Style TargetType="{x:Type Expander}" x:Key="MyExpander">

    <Setter Property="Foreground" Value="{DynamicResource TextBrush}" />
    <Setter Property="Background" Value="Transparent" />
    <Setter Property="HorizontalContentAlignment" Value="Stretch" />
    <Setter Property="VerticalContentAlignment" Value="Stretch" />
    <Setter Property="BorderBrush" Value="Transparent" />
    <Setter Property="BorderThickness" Value="1" />
    <!--<Setter Property="HeaderTemplate" Value="{StaticResource titleText}"/>-->
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Expander}">

                <ControlTemplate.Resources>
                    <Storyboard x:Key="strbExpand">
                        <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="border" Storyboard.TargetProperty="(FrameworkElement.Height)">
                            <SplineDoubleKeyFrame KeyTime="00:00:00" Value="0"/>
                            <SplineDoubleKeyFrame KeyTime="00:00:00.1200000" Value="100"/>
                        </DoubleAnimationUsingKeyFrames>
                    </Storyboard>
                    <Storyboard x:Key="strbCollapse">
                        <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="border" Storyboard.TargetProperty="(FrameworkElement.Height)">
                            <SplineDoubleKeyFrame KeyTime="00:00:00" Value="100"/>
                            <SplineDoubleKeyFrame KeyTime="00:00:00.1200000" Value="0"/>
                        </DoubleAnimationUsingKeyFrames>
                    </Storyboard>
                </ControlTemplate.Resources>


                <Border SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="1,1,1,1" CornerRadius="3" >
                    <DockPanel x:Name="dockPanel">
                        <ToggleButton FontFamily="{TemplateBinding FontFamily}" FontSize="{TemplateBinding FontSize}" FontStretch="{TemplateBinding FontStretch}" FontStyle="{TemplateBinding FontStyle}" FontWeight="{TemplateBinding FontWeight}" 
                                      Foreground="{TemplateBinding Foreground}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" 
                                      FocusVisualStyle="{StaticResource ExpanderHeaderFocusVisual}" Margin="1,1,1,0" MinHeight="0" MinWidth="0" x:Name="HeaderSite" Style="{StaticResource ExpanderDownHeaderStyle}" 
                                      Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" 
                                      ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}" 
                                      IsChecked="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" DockPanel.Dock="Top" />
                        <Border Background="{DynamicResource ShadeBrush}" BorderBrush="{DynamicResource NormalBorderBrush}" BorderThickness="1,0,1,1" CornerRadius="3,3,3,3" x:Name="border" Margin="1,1,1,1" Height="0" >
                            <ContentPresenter x:Name="ExpandSite" Focusable="false" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1,1,1,1"  VerticalAlignment="{TemplateBinding VerticalContentAlignment}" DockPanel.Dock="Bottom" />
                        </Border>
                    </DockPanel>
                </Border>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsExpanded" Value="true">
                        <Trigger.EnterActions>
                            <BeginStoryboard Storyboard="{StaticResource strbExpand}"/>
                        </Trigger.EnterActions>
                        <Trigger.ExitActions>
                            <BeginStoryboard  Storyboard="{StaticResource strbCollapse}"/>
                        </Trigger.ExitActions>
                    </Trigger>

                    <Trigger Property="ExpandDirection" Value="Down">
                        <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Bottom" />
                        <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Top" />
                        <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderDownHeaderStyle}" />
                    </Trigger>
                    <!--<Trigger Property="ExpandDirection" Value="Right">
                        <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right" />
                        <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left" />
                        <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderRightHeaderStyle}" />
                    </Trigger>
                    <Trigger Property="ExpandDirection" Value="Up">
                        <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Top" />
                        <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Bottom" />
                        <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderUpHeaderStyle}" />
                    </Trigger>
                    <Trigger Property="ExpandDirection" Value="Left">
                        <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Left" />
                        <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Right" />
                        <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderLeftHeaderStyle}" />
                    </Trigger>-->
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>