Use IItemContainerGenerator interface.

Instead of ItemContainerGenerator  class.

Perspex.Controls/ItemsControl.cs

@@ -31,7 +31,7 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<ItemsPanelTemplate> ItemsPanelProperty =
             PerspexProperty.Register<ItemsControl, ItemsPanelTemplate>("ItemsPanel", defaultValue: DefaultPanel);
 
-        private ItemContainerGenerator itemContainerGenerator;
+        private IItemContainerGenerator itemContainerGenerator;
 
         private PerspexReadOnlyListView<IVisual, ILogical> logicalChildren = 
             new PerspexReadOnlyListView<IVisual, ILogical>(x => (ILogical)x);
@@ -52,7 +52,6 @@ namespace Perspex.Controls
             this.ItemsChanged(null, null);
         }
 
-        public ItemContainerGenerator ItemContainerGenerator
         {
             get
             {
@@ -100,7 +99,7 @@ namespace Perspex.Controls
             }
         }
 
-        protected virtual ItemContainerGenerator CreateItemContainerGenerator()
+        protected virtual IItemContainerGenerator CreateItemContainerGenerator()
         {
             return new ItemContainerGenerator(this);
         }

Perspex.Controls/ListBox.cs

@@ -11,7 +11,7 @@ namespace Perspex.Controls
 
     public class ListBox : SelectingItemsControl
     {
-        protected override ItemContainerGenerator CreateItemContainerGenerator()
+        protected override IItemContainerGenerator CreateItemContainerGenerator()
         {
             return new TypedItemContainerGenerator<ListBoxItem>(this);
         }

Perspex.Controls/Presenters/DeckPresenter.cs

@@ -38,7 +38,7 @@ namespace Perspex.Controls.Presenters
             this.GetObservableWithHistory(SelectedItemProperty).Subscribe(this.SelectedItemChanged);
         }
 
-        public ItemContainerGenerator ItemContainerGenerator
+        public IItemContainerGenerator ItemContainerGenerator
         {
             get;
             private set;

Perspex.Controls/Primitives/TabStrip.cs

@@ -33,10 +33,10 @@ namespace Perspex.Controls.Primitives
             set { this.SetValue(SelectedTabProperty, value); }
         }
 
-        protected override ItemContainerGenerator CreateItemContainerGenerator()
+        protected override IItemContainerGenerator CreateItemContainerGenerator()
         {
             TabControl tabControl = this.TemplatedParent as TabControl;
-            ItemContainerGenerator result;
+            IItemContainerGenerator result;
 
             if (tabControl != null)
             {

Perspex.Controls/TreeView.cs

@@ -38,7 +38,7 @@ namespace Perspex.Controls
             set { this.SetValue(SelectedItemProperty, value); }
         }
 
-        protected override ItemContainerGenerator CreateItemContainerGenerator()
+        protected override IItemContainerGenerator CreateItemContainerGenerator()
         {
             return new TreeItemContainerGenerator<TreeViewItem>(this);
         }

Perspex.Controls/TreeViewItem.cs

@@ -60,7 +60,7 @@ namespace Perspex.Controls
         }
 
         /// <inheritdoc/>
-        protected override ItemContainerGenerator CreateItemContainerGenerator()
+        protected override IItemContainerGenerator CreateItemContainerGenerator()
         {
             if (this.treeView == null)
             {