Set item container properties with Style priority.

So that they can be overridden by styles.

src/Avalonia.Controls/Generators/ItemContainerGenerator.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 
 namespace Avalonia.Controls.Generators
 {
@@ -187,11 +188,16 @@ namespace Avalonia.Controls.Generators
 
             if (result == null)
             {
-                result = new ContentPresenter
+                result = new ContentPresenter();
+                result.SetValue(ContentPresenter.ContentProperty, item, BindingPriority.Style);
+
+                if (ItemTemplate != null)
                 {
-                    ContentTemplate = ItemTemplate,
-                    Content = item,
-                };
+                    result.SetValue(
+                        ContentPresenter.ContentTemplateProperty,
+                        ItemTemplate,
+                        BindingPriority.TemplatedParent);
+                }
             }
 
             return result;

src/Avalonia.Controls/Generators/ItemContainerGenerator`1.cs

@@ -5,6 +5,7 @@ using System;
 using System.Linq.Expressions;
 using System.Reflection;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 
 namespace Avalonia.Controls.Generators
 {
@@ -62,10 +63,10 @@ namespace Avalonia.Controls.Generators
 
                 if (ContentTemplateProperty != null)
                 {
-                    result.SetValue(ContentTemplateProperty, ItemTemplate);
+                    result.SetValue(ContentTemplateProperty, ItemTemplate, BindingPriority.Style);
                 }
 
-                result.SetValue(ContentProperty, item);
+                result.SetValue(ContentProperty, item, BindingPriority.Style);
 
                 if (!(item is IControl))
                 {

src/Avalonia.Controls/Generators/TreeItemContainerGenerator.cs

@@ -78,7 +78,7 @@ namespace Avalonia.Controls.Generators
                 var template = GetTreeDataTemplate(item, ItemTemplate);
                 var result = new T();
 
-                result.SetValue(ContentProperty, template.Build(item));
+                result.SetValue(ContentProperty, template.Build(item), BindingPriority.Style);
 
                 var itemsSelector = template.ItemsSelector(item);
 

src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs

@@ -43,7 +43,7 @@ namespace Avalonia.Markup.Xaml.Templates
             if (ItemsSource != null)
             {
                 var obs = new ExpressionObserver(item, ItemsSource.Path);
-                return new InstancedBinding(obs);
+                return new InstancedBinding(obs, BindingPriority.Style);
             }
 
             return null;

tests/Avalonia.Controls.UnitTests/Generators/ItemContainerGeneratorTests.cs

@@ -3,8 +3,10 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using System.Reactive.Linq;
 using Avalonia.Controls.Generators;
 using Avalonia.Controls.Presenters;
+using Avalonia.Data;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests.Generators
@@ -111,6 +113,40 @@ namespace Avalonia.Controls.UnitTests.Generators
             Assert.Equal(new[] { 0, 1 }, target.Containers.Select(x => x.Index));
         }
 
+        [Fact]
+        public void Style_Binding_Should_Be_Able_To_Override_Content()
+        {
+            var owner = new Decorator();
+            var target = new ItemContainerGenerator(owner);
+            var container = (ContentPresenter)target.Materialize(0, "foo", null).ContainerControl;
+
+            Assert.Equal("foo", container.Content);
+
+            container.Bind(
+                ContentPresenter.ContentProperty,
+                Observable.Never<object>().StartWith("bar"),
+                BindingPriority.Style);
+
+            Assert.Equal("bar", container.Content);
+        }
+
+        [Fact]
+        public void Style_Binding_Should_Be_Able_To_Override_Content_Typed()
+        {
+            var owner = new Decorator();
+            var target = new ItemContainerGenerator<ListBoxItem>(owner, ListBoxItem.ContentProperty, null);
+            var container = (ListBoxItem)target.Materialize(0, "foo", null).ContainerControl;
+
+            Assert.Equal("foo", container.Content);
+
+            container.Bind(
+                ContentPresenter.ContentProperty,
+                Observable.Never<object>().StartWith("bar"),
+                BindingPriority.Style);
+
+            Assert.Equal("bar", container.Content);
+        }
+
         private IList<ItemContainerInfo> Materialize(
             IItemContainerGenerator generator,
             int index,