Added a "Select Random Item" button to TreeView page.

Causes an exception due to containers not being materialized.

samples/ControlCatalog/Pages/TreeViewPage.xaml

@@ -20,6 +20,7 @@
 
         <Button Command="{Binding AddItemCommand}">Add</Button>
         <Button Command="{Binding RemoveItemCommand}">Remove</Button>
+        <Button Command="{Binding SelectRandomItemCommand}">Select Random</Button>
 
         <ComboBox SelectedIndex="{Binding SelectionMode, Mode=TwoWay}">
           <ComboBoxItem>Single</ComboBoxItem>

samples/ControlCatalog/ViewModels/TreeViewPageViewModel.cs

@@ -23,12 +23,14 @@ namespace ControlCatalog.ViewModels
 
             AddItemCommand = ReactiveCommand.Create(AddItem);
             RemoveItemCommand = ReactiveCommand.Create(RemoveItem);
+            SelectRandomItemCommand = ReactiveCommand.Create(SelectRandomItem);
         }
 
         public ObservableCollection<Node> Items { get; }
         public SelectionModel Selection { get; }
         public ReactiveCommand<Unit, Unit> AddItemCommand { get; }
         public ReactiveCommand<Unit, Unit> RemoveItemCommand { get; }
+        public ReactiveCommand<Unit, Unit> SelectRandomItemCommand { get; }
 
         public SelectionMode SelectionMode
         {
@@ -74,6 +76,15 @@ namespace ControlCatalog.ViewModels
             }
         }
 
+        private void SelectRandomItem()
+        {
+            var random = new Random();
+            var depth = random.Next(4);
+            var indexes = Enumerable.Range(0, 4).Select(x => random.Next(10));
+            var path = new IndexPath(indexes);
+            Selection.SelectedIndex = path;
+        }
+
         private void SelectionChanged(object sender, SelectionModelSelectionChangedEventArgs e)
         {
             var selected = string.Join(",", e.SelectedIndices);