More work on TreeView.

Perspex/Controls/Control.cs

@@ -190,11 +190,11 @@ namespace Perspex.Controls
             get { return Enumerable.Empty<ILogical>(); }
         }
 
-        protected override void AttachedToVisualTree()
+        protected override void OnAttachedToVisualTree()
         {
             IStyler styler = Locator.Current.GetService<IStyler>();
             styler.ApplyStyles(this);
-            base.AttachedToVisualTree();
+            base.OnAttachedToVisualTree();
         }
 
         protected void AddPseudoClass(PerspexProperty<bool> property, string className)

Perspex/Controls/DataTemplate.cs

@@ -46,13 +46,23 @@ namespace Perspex.Controls
     public class DataTemplate<T> : DataTemplate
     {
         public DataTemplate(Func<T, Control> build)
-            : base(typeof(T), o => build((T)o))
+            : base(typeof(T), Cast(build))
         {
         }
 
         public DataTemplate(Func<T, bool> match, Func<T, Control> build)
-            : base(o => (o is T) ? match((T)o) : false, o => build((T)o))
+            : base(CastMatch(match), Cast(build))
         {
         }
+
+        private static Func<object, bool> CastMatch(Func<T, bool> f)
+        {
+            return o => (o is T) ? f((T)o) : false;
+        }
+
+        private static Func<object, TResult> Cast<TResult>(Func<T, TResult> f)
+        {
+            return o => f((T)o);
+        }
     }
 }

Perspex/Controls/TreeDataTemplate.cs

@@ -26,16 +26,38 @@ namespace Perspex.Controls
         {
         }
 
+        public TreeDataTemplate(
+            Type type,
+            Func<object, Control> build,
+            Func<object, IEnumerable> itemsSelector,
+            Func<object, bool> isExpanded)
+            : this(o => IsInstance(o, type), build, itemsSelector, isExpanded)
+        {
+        }
+
         public TreeDataTemplate(
             Func<object, bool> match, 
             Func<object, Control> build,
             Func<object, IEnumerable> itemsSelector)
+            : this(match, build, itemsSelector, _ => false)
+        {
+            this.ItemsSelector = itemsSelector;
+        }
+
+        public TreeDataTemplate(
+            Func<object, bool> match,
+            Func<object, Control> build,
+            Func<object, IEnumerable> itemsSelector,
+            Func<object, bool> isExpanded)
             : base(match, build)
         {
             this.ItemsSelector = itemsSelector;
+            this.IsExpanded = isExpanded;
         }
 
         public Func<object, IEnumerable> ItemsSelector { get; private set; }
+
+        public Func<object, bool> IsExpanded { get; private set; }
     }
 
     public class TreeDataTemplate<T> : TreeDataTemplate
@@ -43,7 +65,15 @@ namespace Perspex.Controls
         public TreeDataTemplate(
             Func<T, Control> build,
             Func<T, IEnumerable> itemsSelector)
-            : base(typeof(T), o => build((T)o), o => itemsSelector((T)o))
+            : base(typeof(T), Cast(build), Cast(itemsSelector))
+        {
+        }
+
+        public TreeDataTemplate(
+            Func<T, Control> build,
+            Func<T, IEnumerable> itemsSelector,
+            Func<T, bool> isExpanded)
+            : base(typeof(T), Cast(build), Cast(itemsSelector), Cast(isExpanded))
         {
         }
 
@@ -51,8 +81,27 @@ namespace Perspex.Controls
             Func<T, bool> match, 
             Func<T, Control> build,
             Func<T, IEnumerable> itemsSelector)
-            : base(o => (o is T) ? match((T)o) : false, o => build((T)o), o => itemsSelector((T)o))
+            : base(CastMatch(match), Cast(build), Cast(itemsSelector))
+        {
+        }
+
+        public TreeDataTemplate(
+            Func<T, bool> match,
+            Func<T, Control> build,
+            Func<T, IEnumerable> itemsSelector,
+            Func<T, bool> isExpanded)
+            : base(CastMatch(match), Cast(build), Cast(itemsSelector), Cast(isExpanded))
+        {
+        }
+
+        private static Func<object, bool> CastMatch(Func<T, bool> f)
+        {
+            return o => (o is T) ? f((T)o) : false;
+        }
+
+        private static Func<object, TResult> Cast<TResult>(Func<T, TResult> f)
         {
+            return o => f((T)o);
         }
     }
 }

Perspex/Controls/TreeView.cs

@@ -25,6 +25,7 @@ namespace Perspex.Controls
                 {
                     Header = template.Build(item),
                     Items = template.ItemsSelector(item),
+                    IsExpanded = template.IsExpanded(item),
                 };
             }
 

Perspex/Controls/TreeViewItem.cs

@@ -11,10 +11,30 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<bool> IsExpandedProperty =
             PerspexProperty.Register<TreeViewItem, bool>("IsExpanded");
 
+        TreeView parent;
+
         public bool IsExpanded
         {
             get { return this.GetValue(IsExpandedProperty); }
             set { this.SetValue(IsExpandedProperty, value); }
         }
+
+        protected override Control CreateItemControlOverride(object item)
+        {
+            if (this.parent != null)
+            {
+                return this.parent.CreateItemControl(item);
+            }
+            else
+            {
+                return null;
+            }
+        }
+
+        protected override void OnAttachedToVisualTree()
+        {
+            base.OnAttachedToVisualTree();
+            this.parent = this.GetVisualParent<Control>().TemplatedParent as TreeView;
+        }
     }
 }

Perspex/Visual.cs

@@ -64,11 +64,11 @@ namespace Perspex
                     IVisual oldValue = this.visualParent;
                     this.visualParent = value;
                     this.InheritanceParent = (PerspexObject)value;
-                    this.VisualParentChanged(oldValue, value);
+                    this.OnVisualParentChanged(oldValue, value);
 
                     if (this.GetVisualAncestor<ILayoutRoot>() != null)
                     {
-                        this.AttachedToVisualTree();
+                        this.NotifyAttachedToVisualTree();
                     }
                 }
             }
@@ -104,21 +104,27 @@ namespace Perspex
             Contract.Requires<ArgumentNullException>(context != null);
         }
 
-        protected virtual void AttachedToVisualTree()
+        protected virtual void OnAttachedToVisualTree()
+        {
+        }
+
+        protected virtual void OnVisualParentChanged(IVisual oldValue, IVisual newValue)
+        {
+        }
+
+        private void NotifyAttachedToVisualTree()
         {
             this.Log().Debug(string.Format(
                 "Attached {0} (#{1:x8}) to visual tree",
                 this.GetType().Name,
                 this.GetHashCode()));
 
+            this.OnAttachedToVisualTree();
+
             foreach (Visual child in ((IVisual)this).ExistingVisualChildren.OfType<Visual>())
             {
-                child.AttachedToVisualTree();
+                child.NotifyAttachedToVisualTree();
             }
         }
-
-        protected virtual void VisualParentChanged(IVisual oldValue, IVisual newValue)
-        {
-        }
     }
 }

Perspex/VisualExtensions.cs

@@ -126,6 +126,16 @@ namespace Perspex
             }
         }
 
+        public static IVisual GetVisualParent(this IVisual visual)
+        {
+            return visual.VisualParent;
+        }
+
+        public static T GetVisualParent<T>(this IVisual visual) where T : class
+        {
+            return visual.VisualParent as T;
+        }
+
         public static IEnumerable<T> GetVisualSiblings<T>(this IVisual visual)
         {
             IVisual parent = visual.VisualParent;

TestApplication/Program.cs

@@ -88,7 +88,8 @@ namespace TestApplication
                 {
                     new TreeDataTemplate<Node>(
                         x => new TextBlock { Text = x.Name },
-                        x => x.Children),
+                        x => x.Children,
+                        x => true),
                 },
             };