WPF context menu bound to List<> dependency property

Question

Im trying to make the contents of a List thats a dependency property show up in a WPF context menu.

I have a class with the following dependency property, a list of Foo's (data holding class):

    public List<Foo> FooList
    {
        get { return (List<Foo>)GetValue(FooListProperty); }
        set { SetValue(FooListProperty, value); }
    }
    public static DependencyProperty FooListProperty =
        DependencyProperty.Register("FooList", typeof(List<Foo>),
            typeof(FooButton));

In XAML I set up the following static resource, I assume its needed since the context menu isnt part of the visual tree:

<UserControl.Resources>
    <ResourceDictionary>            
        <CollectionViewSource 
            x:Key="FooListSource"
            Source="{Binding FooList}"/>

        <!-- ... -->

    </ResourceDictionary>
</UserControl.Resources>

Also part of the ResourceDictionary above is a CompositeCollection which is needed to make the items show up in the actual context menu. If the UserControl CanStop property is true, we also show a separator and a stop command. These bindings does also fail, although the MenuItems themselves show up. So If I can figure out why these fail, the List might be easier.

<CompositeCollection x:Key="FooListItems">
    <CollectionContainer 
        Collection="{Binding Source={StaticResource FooListSource}}"/>
    <Separator 
        Visibility="{Binding CanStop,
            Converter={StaticResource VisibleIfTrue}}" />
    <MenuItem 
        Command="{x:Static Buttons:FooButton.Stop}"
        Header="Stop"
        Visibility="{Binding CanStop,
            Converter={StaticResource VisibleIfTrue}}"/>
</CompositeCollection>

And finally the context menu itself, also in the ResourceDictionary:

<ContextMenu 
    x:Key="FooButtonMenu"
    ItemsSource="{Binding Source={StaticResource FooListItems}}" 
    ItemTemplate="{StaticResource FooListTemplate}"
    <ContextMenu.CommandBindings>
        <CommandBinding  
                Command="{x:Static Buttons:FooButton.Stop}"
                Executed="Stop_Executed" />
    </ContextMenu.CommandBindings>
</ContextMenu>

I feel Im posting way to much code but Im not sure I can make this piece any simpler. Only the separator and the hardcoded menuitem shows up. So something must be messed up with the bindings. Bindings are usually not that hard but now when I want to bind something thats not really part of the same tree I feel a bit lost.

Any suggestions are welcome. :)

Answer 1

I don't see why you've made FooList a dependency property. You're not making it the target of a binding, which is the most common reason to create a dependency property. You haven't implemented a callback, so it can't do change notification (the second most common reason to create a dependency property). You're not using it for value inheritance. So why, then?

It seems to me that what you really want is for FooList to be a normal CLR property of type ObservableCollection<Foo> (or any class that implements INotifyCollectionChanged). That will do all the change notification that you need - at least, that you need for the code you've posted so far.

Answer 2

As you suspected, your problem does seem to be caused by the use of List<Foo> instead of ObservableCollection<Foo>. Since List<Foo> doesn't notify on property changes, the only way to get WPF to recognize you've added or removed an item is to temporarily set the FooList property to something else and then set it back.

There is no need to switch to a CLR property. Just change List<Foo> to ObservableCollection<Foo>.

The reason the bindings in your CompositeCollection aren't working is that CompositeCollection is not a DependencyObject, so it can't inherit a DataContext.