WPF在固定位置的切换按钮下方弹出窗口

Question

我正在尝试构建一个显示ListView的自定义ComboBox。这是我想要实现的屏幕截图：

我的大部分代码都基于this very helpful blog，它讨论了如何在ComboBox中嵌入DataGrid（或者在我的情况下，是GridView）。从功能的角度来看，一切都在发挥作用。但是，我似乎无法找到一种方法来解决下拉问题。理想情况下，无论窗口大小或窗口位置如何，我都希望它始终如上所示。目前，弹出窗口尝试右对齐，除非窗口靠近屏幕的左边缘，此时弹出窗口向内迁移。正如下面的XAML所示，问题是ListView位于Popup内部，而Popups并没有真正绑定到普通窗口，因此我们无法直接控制它们的位置。

<Window.Resources>
  <Style x:Key="ComboBoxTest2" TargetType="{x:Type ComboBox}">
    <Setter Property="Template">
      <Setter.Value>
        <ControlTemplate TargetType="ComboBox">
          <Grid>
            <ToggleButton x:Name="TGButton" Grid.Column="2" Focusable="false"
                          IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,
                          RelativeSource={RelativeSource TemplatedParent}}"
                          Padding="0,0,50,0">
              <ToggleButton.Template>
                <ControlTemplate>
                  <Grid>
                    <Grid.ColumnDefinitions>
                      <ColumnDefinition Width="*" />
                      <ColumnDefinition Width="30" />
                    </Grid.ColumnDefinitions>
                    <Border x:Name="Border" Grid.ColumnSpan="2" CornerRadius="5"
                         Background="LightGray" BorderBrush="Black" BorderThickness="1" />
                    <Border x:Name="Border2" Grid.Column="0" CornerRadius="5,0,0,5"
                            Margin="1" Background="White" BorderBrush="Black"
                            BorderThickness="0,0,1,0" />
                    <Path x:Name="Arrow" Grid.Column="1"  Fill="Black"
                          HorizontalAlignment="Center" VerticalAlignment="Center"
                          Data="M 0 0 L 4 4 L 8 0 Z"/>
                  </Grid>
                  <ControlTemplate.Triggers>
                    <Trigger Property="ToggleButton.IsMouseOver" Value="true">
                      <Setter TargetName="Border" Property="Background" Value="DarkGray" />
                    </Trigger>
                    <Trigger Property="ToggleButton.IsChecked" Value="true">
                      <Setter TargetName="Border" Property="Background" Value="DarkGray" />
                      <Setter TargetName="Border" Property="CornerRadius" Value="5,5,0,0" />
                      <Setter TargetName="Border2" Property="CornerRadius" Value="5,0,0,0" />
                    </Trigger>
                  </ControlTemplate.Triggers>
                </ControlTemplate>
              </ToggleButton.Template>
            </ToggleButton>
            <ContentPresenter Name="ContentSite" IsHitTestVisible="False"
                            Content="{TemplateBinding SelectionBoxItem}"
                            ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
                            ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
                            Margin="3,3,40,3" />
            <TextBox x:Name="PART_EditableTextBox" Visibility="Hidden"
                     IsReadOnly="{TemplateBinding IsReadOnly}" Width="50" />
            <Popup Name="Popup" IsOpen="{TemplateBinding IsDropDownOpen}"
                   AllowsTransparency="True" Focusable="False" PopupAnimation="Slide"
                   Placement="Relative" VerticalOffset="{TemplateBinding ActualHeight}"
                   HorizontalOffset="{TemplateBinding ActualWidth}">
             <Grid Name="DropDown" SnapsToDevicePixels="True"
                   MinWidth="{TemplateBinding ActualWidth}"
                   MaxHeight="{TemplateBinding MaxDropDownHeight}">
               <Border x:Name="DropDownBorder" Background="White" BorderThickness="1"
                       BorderBrush="Black"/>
                 <ListView ItemsSource="{TemplateBinding ItemsSource}"
                           SelectedItem="{Binding RelativeSource={RelativeSource TemplatedParent},
                           Path=SelectedItem}">
                   <ListView.View>
                     <GridView>
                       <GridViewColumn Header="Key" DisplayMemberBinding="{Binding Key}" />
                       <GridViewColumn Header="Name" DisplayMemberBinding="{Binding Name}" />
                     </GridView>
                   </ListView.View>
                 </ListView>
               </Grid>
             </Popup>
           </Grid>
         </ControlTemplate>
       </Setter.Value>
     </Setter>
   </Style>
 </Window.Resources>
<Grid>
  <ComboBox x:Name="cBox" Height="30" Width="200" ItemsSource="{Binding Path=People}"
            SelectedValue="Selected" DisplayMemberPath="Name" SelectedValuePath="Name"
            Style="{StaticResource ComboBoxTest2}" 
            SelectionChanged="Function_SelectionChanged" />
</Grid>

我在一些地方读过，Adorners可能是一个解决方案，因为他们会收到所有resize事件并可以动态重新定位弹出窗口。另一种选择可能是使用像DevExpress这样的库，但我试图避免这种情况。顺便说一句，我的问题不是this one的副本，因为用于在XAML中放置Popup的偏移仅在渲染时受到尊重，而不是在调整大小/移动时。