How to stretch the content of a templated MenuItem using WPF - wpf

Question

in my WPF application I have a Menu defined as follows:
<Menu
Grid.Column="1"
MinWidth="50"
MinHeight="50"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
Background="Transparent"
Visibility="{Binding Path=ShowSynergies, Converter={StaticResource BoolToVisConverter}}">
<Menu.ItemsPanel>
<ItemsPanelTemplate>
<Grid />
</ItemsPanelTemplate>
</Menu.ItemsPanel>
<MenuItem
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
VerticalContentAlignment="Stretch"
BorderBrush="Black"
BorderThickness="1"
ItemsSource="{Binding Path=CurrentlyAvailableSynergies, Source={StaticResource ResourceKey=VM}}">
<MenuItem.Header>
<TextBlock
Margin="5"
FontSize="18"
Text="{Binding Path=ActiveSynergy.Synergy, Source={StaticResource ResourceKey=VM}}"
TextAlignment="Center" />
</MenuItem.Header>
<MenuItem.ToolTip>
<TextBlock Text="{Binding Path=ActiveSynergy.Synergy, Source={StaticResource ResourceKey=VM}}" />
</MenuItem.ToolTip>
<MenuItem.Resources>
<HierarchicalDataTemplate DataType="{x:Type ent:VisualSynergy}" ItemsSource="{Binding Path=AvailableDiameters}">
<TextBlock Text="{Binding SynergyText}"/>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type ent:VisualDiameter}">
<TextBlock
VerticalAlignment="Stretch"
Background="Purple"
Text="{Binding Path=VisualValue}">
<intr:Interaction.Triggers>
<intr:EventTrigger EventName="PreviewMouseLeftButtonDown">
<intr:InvokeCommandAction Command="{Binding Path=SelectSynergyCommand}">
<intr:InvokeCommandAction.CommandParameter>
<MultiBinding Converter="{StaticResource ResourceKey=StdMultiConverter}">
<Binding Path="." />
<Binding Path="." Source="{StaticResource ResourceKey=VM}" />
</MultiBinding>
</intr:InvokeCommandAction.CommandParameter>
</intr:InvokeCommandAction>
</intr:EventTrigger>
</intr:Interaction.Triggers>
</TextBlock>
</DataTemplate>
</MenuItem.Resources>
</MenuItem>
</Menu>
Everything is working as intended, all data is bound properly and updated when it should be updated.
My larges issue is that the final TextBlock (the one related to my VisualDiameter type) doe snot stretch to fill the whole MenuItem available space (see screenshot). I've tried also to redefine styles, but since I am inside the MenuItem resources definitions there is something missing and no stretching happens.
Looking ot other questions my issue seems related to the bizzarre definition of TreeView and MenuItem by Microsoft, but I am not confidend enough to start tinkering with basic templates.

Answer 1

You should define an ItemContainerStyle and bind the Command property of the MenuItem container rather than trying to stretch the TextBlock in the DataTemplate:
<MenuItem
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
VerticalContentAlignment="Stretch"
BorderBrush="Black"
BorderThickness="1"
ItemsSource="{Binding Path=CurrentlyAvailableSynergies}">
<MenuItem.ItemContainerStyle>
<Style TargetType="MenuItem">
<Setter Property="Command" Value="{Binding SelectSynergyCommand}" />
</Style>
</MenuItem.ItemContainerStyle>
<MenuItem.Header>
...