How to hide the separator in the context menu using MultiBinding?

Question

I am using the context menu in the wpf tree, and I'm pretty much sure what I want. Before I explain the problem, let me explain what the XAML definition for the context menu does.

For each menu item in the context menu, we have a command that either disables or enables the menu item based on CanExecute commands. Each command will set the IsEnabled property of the corresponding menu item depending on the result of CanExecute.

The IsEnabled for each menu item is bound to a BooleanToVisibilityConverter, which converts the bool value of IsEnabled to a Collapse or Visible value to bind the visibility property of the menu item. This works fine again, and my menu items show and hide.

Now for the problem. In the XAML below, we have two menu items (addCategoryMenuItem and removeCategoryMenuItem) above the separator. I am trying to use the MultiBinding for the IsEnabled property of these two menu items using a special implementation of IMultiValueConverter (MultiBooleanToVisibilityConverter), so that when two menu items are disabled, I can set the Separator Visibility property to collapse and therefore hide the separator when menu items are disabled.

For the Convert method in my converter (MultiBooleanToVisibilityConverter) the parameter value (object values ​​[]) I get two elements in the array that contain the value "{DependencyProperty.UnsetValue}". They cannot be added to boolean values ​​and therefore my Visibility value cannot be worked out.

, - ElementName, MultiBinding. ? RelativeSource. .. . , .

<ContextMenu x:Key="CategoryMenu">
    <ContextMenu.ItemContainerStyle>
        <Style TargetType="{x:Type Control}">
            <Setter Property="Visibility" Value="{Binding Path=IsEnabled, RelativeSource={RelativeSource Self}, Mode=OneWay, Converter={StaticResource booleanToVisibilityConverter}}" />
        </Style>
    </ContextMenu.ItemContainerStyle>
    <ContextMenu.Items>
        <MenuItem x:Name="addCategoryMenuItem" Header="add category" Command="{Binding AddCategory}">
            <MenuItem.Icon>
                <Image Source="/Images/add.png" Width="16" Height="16" />
            </MenuItem.Icon>
        </MenuItem>
        <MenuItem x:Name="removeCategoryMenuItem" Header="remove category" Command="{Binding RemoveCategory}">
            <MenuItem.Icon>
                <Image Source="/Images/remove.png" Width="16" Height="16" />
            </MenuItem.Icon>
        </MenuItem>
        <Separator>
            <Separator.Visibility>
                <MultiBinding Converter="{StaticResource multiBooleanToVisibilityConverter}">
                    <Binding Mode="OneWay" ElementName="addCategoryMenuItem" Path="IsEnabled" />
                    <Binding Mode="OneWay" ElementName="removeCategoryMenuItem" Path="IsEnabled" />
                </MultiBinding>
            </Separator.Visibility>
        </Separator>
        <MenuItem x:Name="refreshCategoryMenuItem" Header="refresh" Command="{Binding RefreshCategory}">
            <MenuItem.Icon>
                <Image Source="/Images/refresh.png" Width="16" Height="16" />
            </MenuItem.Icon>
        </MenuItem>
    </ContextMenu.Items>
</ContextMenu>

Answer 1

, . RelativeSource FindAncestor, , , . , , , xaml.

<Separator>
    <Separator.Visibility>
        <MultiBinding Converter="{StaticResource multiBooleanToVisibilityConverter}">
            <Binding Mode="OneWay" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}" Path="Items[0].IsEnabled" />
            <Binding Mode="OneWay" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}" Path="Items[1].IsEnabled" />
        </MultiBinding>
    </Separator.Visibility>
</Separator>

Answer 2

, , , ItemsControl.

public class AutoVisibilitySeparator : Separator
{
    public AutoVisibilitySeparator()
    {
        if (DesignerProperties.GetIsInDesignMode(this))
            return;

        Visibility = Visibility.Collapsed; // Starting collapsed so we don't see them disappearing

        Loaded += OnLoaded;
    }

    private void OnLoaded(object sender, RoutedEventArgs e)
    {
        // We have to wait for all siblings to update their visibility before we update ours.
        // This is the best way I've found yet. I tried waiting for the context menu opening or visibility changed, on render and lots of other events
        Dispatcher.BeginInvoke(new Action(UpdateVisibility), DispatcherPriority.Render);
    }

    private void UpdateVisibility()
    {
        var showSeparator = false;

        // Go through each sibling of the parent context menu looking for a visible item before and after this separator
        var foundThis = false;
        var foundItemBeforeThis = false;
        foreach (var visibleItem in ((ItemsControl)Parent).Items.OfType<UIElement>().Where(i => i.Visibility == Visibility.Visible || i == this))
        {
            if (visibleItem == this)
            {
                // If there were no visible items prior to this separator then we hide it
                if (!foundItemBeforeThis)
                    break;

                foundThis = true;
            }
            else if (visibleItem is AutoVisibilitySeparator || visibleItem is Separator)
            {
                // If we already found this separator and this next item is not a visible item we hide this separator
                if (foundThis)
                    break;

                foundItemBeforeThis = false; // The current item is a separator so we reset the search for an item
            }
            else
            {
                if (foundThis)
                {
                    // We found a visible item after finding this separator so we're done and should show this
                    showSeparator = true;
                    break;
                }

                foundItemBeforeThis = true;
            }
        }

        Visibility = showSeparator ? Visibility.Visible : Visibility.Collapsed;
    }
}