CommandParameter with MVVM Light

Question

I'm trying to get a RelayCommand working with a CommandParameter working using MVVM Light. The command is defined in my viewmodel, and I want to pass the selected ListBox item as the parameter. The command is bound, but the parameter is not. Is this possible?

<UserControl x:Class="Nuggets.Metro.Views.EmployeeListView"
         ...
         DataContext="{Binding EmployeeList,Source={StaticResource Locator}}">
   <ListBox x:Name="lstEmployee" ItemsSource="{Binding EmployeeItems}" Style="{StaticResource EmployeeList}" Tag="{Binding EmployeeItems}">
        <ListBox.ContextMenu>
            <ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
                <MenuItem Header="Edit item" Command="{Binding EditEmployeeCommand}" CommandParameter="{Binding PlacementTarget.SelectedItem,RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}"/>
                <MenuItem Header="Delete item" Command="{Binding DeleteEmployeeCommand}" CommandParameter="{Binding PlacementTarget.SelectedItem,RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}"/>
            </ContextMenu>
        </ListBox.ContextMenu>

Answer 1

This should work

<ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
  <MenuItem Header="Edit item" 
            Command="{Binding EditEmployeeCommand}" 
            CommandParameter="{Binding SelectedItem,ElementName=lstEmployee}"/>
  <MenuItem Header="Delete item" 
            Command="{Binding DeleteEmployeeCommand}"
            CommandParameter="{Binding SelectedItem,ElementName=lstEmployee}"/>
 </ContextMenu>

Use the Name of your ListBox als ElementName in the binding of the CommandParameter and set the path to SelectedItem.

Update:

The above code does not work for ListBox and ContextMenu, cause they belong to diffrent visual trees. The result is

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=lstEmployee'. BindingExpression:Path=SelectedItem; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'CommandParameter' (type 'Object')

The following XAML does the job. Using the PlacementTarget (that is the ListBox) of the ContextMenu.

<ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
  <MenuItem Header="Edit item" 
            Command="{Binding EditEmployeeCommand}" 
            CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu}, Path=PlacementTarget.SelectedItem}"/>
  <MenuItem Header="Delete item" 
            Command="{Binding DeleteEmployeeCommand}"
            CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu}, Path=PlacementTarget.SelectedItem}"/>
</ContextMenu>

Answer 2

This works for TreeView or ListView with MVVM. The PlacementTarget from the ContextMenu is (here) the Listview

<ListView.ContextMenu>
  <ContextMenu>
     <MenuItem x:Name="OpenExplorer"Header="ShowFolder"                  
      Command="{Binding ShowExplorer}"
      CommandParameter ="{Binding Path=PlacementTarget.SelectedItem,
            RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
   </ContextMenu>
</ListView.ContextMenu>