Proper way to use CollectionViewSource in ViewModel

I used Drag and Drop to bind Data Source object (a DB model) to DataGrid (basically following this example in Entity Framework Databinding with WPF.

Everything works fine with this implementation.

XAML

<Window.Resources>    
<CollectionViewSource x:Key="categoryViewSource"  
    d:DesignSource="{d:DesignInstance {x:Type local:Category}, CreateList=True}"/>
</Window.Resources>
<Grid DataContext="{StaticResource categoryViewSource}">
..

Code Behind

private void Window_Loaded(object sender, RoutedEventArgs e)
{
   System.Windows.Data.CollectionViewSource categoryViewSource =
      ((System.Windows.Data.CollectionViewSource)(this.FindResource("categoryViewSource")));

  _context.Categories.Load();
  categoryViewSource.Source = _context.Categories.Local;        
}

ViewModel

public MainWindow()
{
    InitializeComponent();
    this.DataContext = new MyViewModel();
}

However, when I try to use the same code from within ViewModel, it doesn‘t work (FindResource is not available), besides, I don’t think this is the right approach (i.e. to use x:Key in MVVM).

I would really appreciate any help to point me what is the right way to implement CollectionViewSource and DataBinding with DataGrid.