Using MVVM, how can a ContextMenu ViewModel find the ViewModel that opened the ContextMenu?

c#, contextmenu, mvvm, wpf

Solution

I solved this by handling the ContextMenuOpening event on the parent control (the one that owned the ContextMenu in the View). I also added a Context property to IMenuItem. The handler looks like this:

    private void stackPanel_ContextMenuOpening(
        object sender, ContextMenuEventArgs e)
    {
        StackPanel sp = sender as StackPanel;
        if (sp != null)
        {
            // solutionItem is the "context"
            ISolutionItem solutionItem =
                sp.DataContext as ISolutionItem;
            if (solutionItem != null) 
            {
                IEnumerable<IMenuItem> items = 
                    solutionItem.ContextMenu as IEnumerable<IMenuItem>;
                if (items != null)
                {
                    foreach (IMenuItem item in items)
                    {
                        // will automatically set all 
                        // child menu items' context as well
                        item.Context = solutionItem;
                    }
                }
                else
                {
                    e.Handled = true;
                }
            }
            else
            {
                e.Handled = true;
            }
        }
        else
        {
            e.Handled = true;
        }
    }

This takes advantage of the fact that there can only be one ContextMenu open at a time.

Problem

I'm using MVVM to bind views to objects in a Tree. I have a base class that implements the items in my tree, and that base class has a ContextMenu property: ``` public IEnumerable<IMenuItem> ContextMenu { get { return m_ContextMenu; } protected set { if (m_ContextMenu != value) { m_ContextMenu = value; NotifyPropertyChanged(m_ContextMenuArgs); } } } private IEnumerable<IMenuItem> m_ContextMenu = null; static readonly PropertyChangedEventArgs m_ContextMenuArgs = NotifyPropertyChangedHelper.CreateArgs<AbstractSolutionItem>(o => o.ContextMenu); ``` The View that binds to the base class (and all derived classes) implements a ContextMenu that binds to that property: ``` <ContextMenu x:Name="contextMenu" ItemsSource="{Binding Path=(local:AbstractSolutionItem.ContextMenu)}" IsEnabled="{Binding Path=(local:AbstractSolutionItem.ContextMenuEnabled)}" ItemContainerStyle="{StaticResource contextMenuStyle}"/> ``` Each item in the menu is bound to an IMenuItem object (a ViewModel for the menu items). When you click on the menu item, it uses Commands to execute a command on the base object. This all works great. However, once the command is executing on the IMenuItem class, it sometimes needs to get a reference to the object that the user right clicked on to bring up the context menu (or the ViewModel of that object, at least). That's the whole point of a context menu. How should I go about passing the reference of the tree item ViewModel to the MenuItem ViewModel? Note that some context menus are shared by many objects in the tree.

Original source