Custom WPF-WindowStyle: How to recognize click on custom help button? - wpf

Question

I've got a custom Style for my WPF Windows. One part of it is an additional HelpButton next to the regular minimize, maximize and Close button. Assigning this style to my Windows works as expected, but how does my window notice that this button was clicked? The button is defined in the style so my window does not really know about it. Here's the code for the style:
<ResourceDictionary x:Class="Company.Common.Themes.CompanyWindowStyle"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/Company.Common.Themes;component/CompanyWindowBaseStyle.xaml" />
</ResourceDictionary.MergedDictionaries>
<Style x:Key="CompanyWindowStyle"
BasedOn="{StaticResource CompanyWindowBaseStyle}"
TargetType="{x:Type Window}">
<Setter Property="ResizeMode"
Value="CanResize" />
<EventSetter Event="Loaded"
Handler="WindowLoaded" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Window}">
<Border x:Name="PART_Container"
Padding="7,7,7,5">
<Grid TextOptions.TextFormattingMode="Display"
TextOptions.TextRenderingMode="ClearType">
<Border x:Name="PART_Border"
Width="Auto"
Height="Auto"
Background="{StaticResource BackgroundBrush}"
BorderBrush="{StaticResource BorderBrush}"
BorderThickness="1">
<DockPanel HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
Background="Transparent">
<Border x:Name="TitleBar"
Background="{StaticResource BackgroundBrush}"
BorderThickness="0"
DockPanel.Dock="Top"
MouseDown="TitleBarMouseDown">
<Grid Height="32"
Background="Transparent">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="36" />
<ColumnDefinition />
<ColumnDefinition Width="34" />
<ColumnDefinition Width="34" />
<ColumnDefinition Width="34" />
<ColumnDefinition Width="34" />
</Grid.ColumnDefinitions>
<ContentControl Grid.Column="0"
MouseDoubleClick="IconMouseDoubleClicked">
<Image x:Name="Icon"
Width="32"
Height="32"
Margin="4,-7,0,7"
HorizontalAlignment="Right"
WindowChrome.IsHitTestVisibleInChrome="True"
Source="{Binding Path=Icon,
Mode=OneWay,
RelativeSource={RelativeSource TemplatedParent}}" />
</ContentControl>
<TextBlock x:Name="Caption"
Grid.Column="1"
Margin="4,0,0,0"
HorizontalAlignment="Center"
VerticalAlignment="Center"
FontFamily="Segoe UI"
FontSize="12"
Opacity="0.66"
Text="{Binding Path=Title,
Mode=OneWay,
RelativeSource={RelativeSource TemplatedParent}}" />
<Button x:Name="HelpButton"
Grid.Column="2"
Width="34"
Height="26"
VerticalAlignment="Top"
Click="HelpButtonClick"
Style="{StaticResource TitleBarButtonStyle}"
WindowChrome.IsHitTestVisibleInChrome="True">
<Grid MaxWidth="9"
MaxHeight="9">
<TextBlock Text="?" FontSize="14"
Foreground="{Binding RelativeSource={RelativeSource AncestorType=Button},
Path=Foreground}" />
</Grid>
</Button>
<Button x:Name="MinButton"
Grid.Column="3"
Width="34"
Height="26"
VerticalAlignment="Top"
Click="MinButtonClick"
Style="{StaticResource TitleBarButtonStyle}"
WindowChrome.IsHitTestVisibleInChrome="True">
<Grid MaxWidth="9"
MaxHeight="9">
<Path Data="M0,8 H8 M0,7 H8 M0,6 H8"
RenderOptions.EdgeMode="Aliased"
Stretch="None"
Stroke="{Binding RelativeSource={RelativeSource AncestorType=Button},
Path=Foreground}"
StrokeThickness="1" />
</Grid>
</Button>
<Button x:Name="MaxButton"
Grid.Column="4"
Width="34"
Height="26"
VerticalAlignment="Top"
Click="MaxButtonClick"
Style="{StaticResource TitleBarButtonStyle}"
WindowChrome.IsHitTestVisibleInChrome="True">
<Grid MaxWidth="9"
MaxHeight="9">
<Path x:Name="PART_MaxButton_Path"
Data="M0,0 H8 V8 H0 V0 M0,1 H8 M0,2 H8"
RenderOptions.EdgeMode="Aliased"
Stretch="None"
Stroke="{Binding RelativeSource={RelativeSource AncestorType=Button},
Path=Foreground}"
StrokeThickness="1" />
</Grid>
</Button>
<Button x:Name="CloseButton"
Grid.Column="5"
Width="34"
Height="26"
VerticalAlignment="Top"
Click="CloseButtonClick"
Style="{StaticResource TitleBarButtonStyle}"
WindowChrome.IsHitTestVisibleInChrome="True">
<Grid MaxWidth="9"
MaxHeight="9">
<Path Data="M0,0 L8,8 M0,8 L8,0"
Stretch="None"
Stroke="{Binding RelativeSource={RelativeSource AncestorType=Button},
Path=Foreground}"
StrokeThickness="1.5" />
</Grid>
</Button>
</Grid>
</Border>
<ContentPresenter />
</DockPanel>
</Border>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="WindowState"
Value="Maximized">
<Setter TargetName="PART_MaxButton_Path"
Property="Data"
Value="M0,3 H5 V8 H0 V3 M0,4 H5 M3,0 H8 V5 H7 M3,1 H8" />
</Trigger>
<Trigger Property="WindowState"
Value="Normal">
<Setter TargetName="PART_Border"
Property="Effect">
<Setter.Value>
<DropShadowEffect BlurRadius="7"
Direction="315"
Opacity="0.5"
ShadowDepth="2"
Color="black" />
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsActive"
Value="False">
<Setter TargetName="PART_Border"
Property="BorderBrush"
Value="{StaticResource BorderBrushInactive}" />
</Trigger>
<Trigger Property="IsActive"
Value="True">
<Setter TargetName="PART_Border"
Property="BorderBrush"
Value="{StaticResource BorderBrush}" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ResourceDictionary>
I have somehow no idea how it is done. Can someone please point me in the right direction?
UPDATE:
This is the header of my MainWindow's XAML where I use the Style:
<Window x:Class="Company.MainGUI.GUI.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:common="clr-namespace:Company.Common;assembly=Company.Common"
xmlns:controls="clr-namespace:Company.Common.Controls;assembly=Company.Common.Controls"
xmlns:l="clr-namespace:Company.Common.Languages;assembly=Company.Common.Languages"
xmlns:local="clr-namespace:Company.MainGUI.GUI"
Title="{x:Static l:Common_Text.Application_Name}"
UseLayoutRounding="True"
MinWidth="900"
MinHeight="600"
Icon="pack://application:,,,/Company.Common.Images;component/Resources/ApplicationLogo_MainGUI.ico"
WindowStartupLocation="CenterScreen">
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/Company.Common.Themes;component/CompanyWindowStyle.xaml" />
<ResourceDictionary Source="pack://application:,,,/Company.Common.Themes;component/MainGUISkin.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Window.Resources>
<Window.Style>
<Style TargetType="{x:Type local:MainWindow}"
BasedOn="{StaticResource CompanyWindowStyle}" />
</Window.Style>