Populating MenuItem with composite collection "doubling" up

Question

I'm trying to populate a menu item with a collection of children items. That was easy, however I need to add an extra that's always present that performs an "add" operation. I used a composite collection to add this on to the existing collection of items that need to be displayed.

Here's the code:

<MenuItem Header="Time Ranges" x:Name="TimeRangesMenuItem"
        Background="{StaticResource TitleBarButtonBackgroundBrush}"
        Margin="2">
    <MenuItem.Resources>
        <CollectionViewSource Source="{Binding ElementName=TimeRangesMenuItem, Path=DataContext.TimeSpans}" x:Key="TimeSpanMenuItems" />
    </MenuItem.Resources>
    <MenuItem.ItemsSource>
        <CompositeCollection>
            <CollectionContainer Collection="{Binding Source={StaticResource TimeSpanMenuItems}}" />
            <Separator />
            <MenuItem Header="Add New" cal:Message.Attach="NewTimeSpan()" />
        </CompositeCollection>
    </MenuItem.ItemsSource>
    <MenuItem.ItemTemplate>
        <ItemContainerTemplate>
            <MenuItem Header="{Binding Name}" cal:Message.Attach="ConfigureTimeSpan()" />
        </ItemContainerTemplate>
    </MenuItem.ItemTemplate>
</MenuItem>

It works, almost. The DataContext.TimeSpans ViewModel's I'm trying to display are "nested" inside two MenuItems, rather than just populating one, so I get this strange behavior (this only has a single TimeSpanViewModel "Time Span":

Mouse outside the "inner" MenuItem. Note, the inner one is functional if you press it:

Normal MenuItem:

Anyone got any ideas on how to fix this?

Answer 1

What is an item ItemContainerTemplate...

I think you want to manipulate the MenuItem.ItemContainerStyle instead, otherwise you create two MenuItems as observed.

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The MenuItem.ItemTemplate already defines what is inside the given item container (varies by control, here MenuItem, in a ComboBox it's a ComboBoxItem, etc.). As there does not appear to be an ItemContainerTemplate property on the MenuItem you might only be able to use it that way implementing a selector that returns your template and setting it as ItemContainerTemplateSelector.