DataGrid add CompiledBinding example

samples/ControlCatalog/Pages/DataGridPage.xaml

@@ -1,5 +1,5 @@
 <UserControl xmlns="https://github.com/avaloniaui"
-             xmlns:local="clr-namespace:ControlCatalog.Models;assembly=ControlCatalog"
+             xmlns:local="using:ControlCatalog.Models"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="ControlCatalog.Pages.DataGridPage">
   <UserControl.Resources>
@@ -26,7 +26,8 @@
         <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
           <DataGrid.Columns>
             <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" />
-            <DataGridTextColumn Header="Region" Binding="{Binding Region}" Width="4*" />
+            <!-- CompiledBinding example of usage. -->
+            <DataGridTextColumn Header="Region" Binding="{CompiledBinding Region}" Width="4*" x:DataType="local:Country" />
             <DataGridTextColumn Header="Population" Binding="{Binding Population}" Width="3*" />
             <DataGridTextColumn Header="Area" Binding="{Binding Area}" Width="3*" />
             <DataGridTextColumn Header="GDP" Binding="{Binding GDP}" Width="3*" CellStyleClasses="gdp" />

samples/ControlCatalog/Pages/DataGridPage.xaml.cs

@@ -24,8 +24,10 @@ namespace ControlCatalog.Pages
             dg1.LoadingRow += Dg1_LoadingRow;
             dg1.Sorting += (s, a) =>
             {
-                var property = ((a.Column as DataGridBoundColumn)?.Binding as Binding).Path;
-                if (property == dataGridSortDescription.PropertyPath
+                var binding = (a.Column as DataGridBoundColumn)?.Binding as Binding;
+
+                if (binding?.Path is string property
+                    && property == dataGridSortDescription.PropertyPath
                     && !collectionView1.SortDescriptions.Contains(dataGridSortDescription))
                 {
                     collectionView1.SortDescriptions.Add(dataGridSortDescription);