Quiero colocar una ventana emergente debajo de un botón de alternancia cuando hago clic en él. En esta ventana emergente quiero agregar el botón y otros controles. Pero, ¿cómo puedo asegurarme de que la ventana emergente siempre estará debajo de mi botón de alternancia también cuando cambie el tamaño de mi ventana mian?

Mi código XAML:

     <ToggleButton
    x:Name="userBtn"
    Margin="610,25,378,0"
    VerticalAlignment="Top"            
    Height="29"
    Grid.Column="2" 
    >
        <ToggleButton.Resources>
            <BitmapImage x:Key="imgNormal" UriSource="/Resources/home.jpg"/>
            <BitmapImage x:Key="imgHover" UriSource="/Resources/home_checked.jpg"/>
            <BitmapImage x:Key="imgChecked" UriSource="/Resources/home_checked.jpg"/>
        </ToggleButton.Resources>
        <ToggleButton.Style>
            <Style TargetType="ToggleButton">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="ToggleButton" >
                            <StackPanel Orientation="Horizontal" VerticalAlignment="Top" Width="150" Height="32">
                                <Image x:Name="PART_Image" Height="22" Width="22" RenderOptions.BitmapScalingMode="HighQuality" HorizontalAlignment="Center" Margin="0,0,0,0" Source="{StaticResource imgNormal}"/>
                                <TextBlock x:Name="PART_TEXT" FontFamily="Arial" Foreground="#FFAFADAD" FontSize="13" HorizontalAlignment="Center" Text="{x:Static properties:Resources.BtnDashboard}"  Margin="10,9,0,0"></TextBlock>
                            </StackPanel>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsChecked" Value="true">
                                    <Setter TargetName="PART_Image" Property="Source" Value="{StaticResource imgChecked}"/>
                                    <Setter TargetName="PART_TEXT" Property="Foreground" Value="#79B539" />
                                </Trigger>
                                <Trigger Property="IsMouseOver" Value="true">
                                    <Setter TargetName="PART_Image" Property="Source" Value="{StaticResource imgHover}"/>
                                    <Setter TargetName="PART_TEXT" Property="Foreground" Value="#79B539" />
                                </Trigger>
                                <Trigger Property="IsEnabled" Value="false">
                                    <Setter TargetName="PART_Image" Property="Opacity" Value="0.6"/>
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </ToggleButton.Style>
    </ToggleButton>

    <Popup Name="UserMenuPopUp" PopupAnimation="Fade" Width="280" Height="auto" Margin="20" AllowsTransparency="True" HorizontalAlignment="Left" Placement="bottom" PlacementTarget="{Binding ElementName=userBtn}" IsOpen="{Binding IsChecked, ElementName=Userbtn}" StaysOpen="false" >
        <Border Margin="2,0,48,0" BorderThickness="1" Background="#EEEEEE" Height="105">
            <Grid>

            </Grid>
        </Border>
    </Popup>

Código C # para hacer clic en togglebutton:

    private void UserBtn_Click(object sender, RoutedEventArgs e)
    {
        // Get location, adn sender
        var element = (System.Windows.Controls.Primitives.ToggleButton)sender;
        var location = element.PointToScreen(new Point(0, 0));

        // Set popup location
        UserMenuPopUp.HorizontalOffset = (location.X);
        UserMenuPopUp.VerticalOffset = (location.Y);
        UserMenuPopUp.IsOpen = true;
    }