Xceed Datagrid loses SelectedItem when child selected - mvvm

Question

I have an Xceed datagrid in a WPF MVVM application which is set up to hold master-detail records. When a child row is selected, I want the ViewModel to detect the selected child. I would like to do this preferably with zero code-behind. I have written code which executes an action on the selected item when a contextmenu is clicked. This works correctly when a parent is selected, but always returns null when a child is selected.
I have put together a very simplified version of what I am trying to acheive:
My XAML is:
<Window x:Class="MasterDetailSelection.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:xcdg="clr-namespace:Xceed.Wpf.DataGrid;assembly=Xceed.Wpf.DataGrid.v4.2"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.Resources>
<xcdg:DataGridCollectionViewSource x:Key="cvs_parents" Source="{Binding Path=Parents}">
<xcdg:DataGridCollectionViewSource.DetailDescriptions>
<xcdg:PropertyDetailDescription RelationName="Children"
AutoCreateDetailDescriptions="False">
</xcdg:PropertyDetailDescription>
</xcdg:DataGridCollectionViewSource.DetailDescriptions>
</xcdg:DataGridCollectionViewSource>
</Grid.Resources>
<xcdg:DataGridControl x:Name="ParentGrid"
NavigationBehavior="RowOnly"
ItemsSource="{Binding Source={StaticResource cvs_parents}}"
SelectedItem="{Binding SelectedItem}"
AutoCreateDetailConfigurations="True"
ReadOnly="True">
<xcdg:DataGridControl.ContextMenu>
<ContextMenu DataContext="{Binding PlacementTarget, RelativeSource={RelativeSource Self}}">
<MenuItem Header="Execute Command"
CommandParameter="{Binding DataContext.SelectedItem}"
Command="{Binding DataContext.SampleCommand}" />
</ContextMenu>
</xcdg:DataGridControl.ContextMenu>
</xcdg:DataGridControl>
</Grid>
</Window>
The View Model is:
namespace MasterDetailSelection
{
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using Microsoft.Practices.Composite.Presentation.Commands;
public class ViewModel : INotifyPropertyChanged
{
private ObservableCollection<Parent> _parents;
public event PropertyChangedEventHandler PropertyChanged;
private DelegateCommand<Object> _sampleCommand;
private object _selectedItem;
public ObservableCollection<Parent> Parents
{
get { return _parents; }
set
{
_parents = value;
OnPropertyChanged("Parents");
}
}
public DelegateCommand<Object> SampleCommand
{
get
{
if (_sampleCommand == null)
{
_sampleCommand = new DelegateCommand<object>(ExecuteSampleCommand, CanExecuteSampleCommand);
OnPropertyChanged("SampleCommand");
}
return _sampleCommand;
}
}
public bool CanExecuteSampleCommand(Object commandParameter)
{
return true;
}
public void ExecuteSampleCommand(Object commandParameter)
{
Console.WriteLine("ExecuteSampleCommand");
}
public object SelectedItem
{
get { return _selectedItem; }
set
{
if (_selectedItem != value)
{
_selectedItem = value;
OnPropertyChanged("SelectedItem");
}
}
}
public void LoadParents()
{
var parents = new ObservableCollection<Parent>()
{
new Parent()
{
Id=1,
Description = "Parent1",
Children = new List<Child>(){new Child() {Id = 1, Description = "Child1"} }
}
};
Parents = parents;
}
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
There are 2 simple entities:
public class Parent
{
public int Id { get; set;}
public string Description { get; set;}
public IEnumerable<Child> Children { get; set;}
}
public class Child
{
public int Id { get; set; }
public string Description { get; set; }
}
The OnStartup override in App.xaml.cs contains the following:
var viewModel = new ViewModel();
var window = new MainWindow();
window.DataContext = viewModel;
viewModel.LoadParents();
window.Show();
Whenever i select the parent row, the SelectedItem setter is called with a populated object. When I selected a child row, the same setter is called, but with a null value.
Is there any way I can get a reference to the selected item when the context menu is clicked on a child row - and do this without code-behind. If not, is it possible with code-behind?

Answer 1

Perhaps you should set a context menu directly on the cells or row like below. Then you can send the appropriate model to the command. In the example below I use a static locator class that has my VM to bind the actual command too.
<Style TargetType="{x:Type xcdg:DataCell}">
<Setter Property="ContextMenu" Value="{StaticResource CellContextMenu}">
<Setter.Value>
<ContextMenu>
<MenuItem Header="Execute Command"
CommandParameter="{Binding}"
Command="{Binding Source={StaticResource Locator} Path=ViewModel.SampleCommand}" />
</ContextMenu>
</Setter.Value>
</Setter>
</Style>