Lots of changes involving ItemsControls.

Added ItemContainerGenerator mainly...

Perspex.Base/IReadOnlyPerspexList.cs

@@ -0,0 +1,16 @@
+// -----------------------------------------------------------------------
+// <copyright file="IReadOnlyPerspexList.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex
+{
+    using System.Collections.Generic;
+    using System.Collections.Specialized;
+    using System.ComponentModel;
+
+    public interface IReadOnlyPerspexList<T> : IReadOnlyList<T>, INotifyCollectionChanged, INotifyPropertyChanged
+    {
+    }
+}

Perspex.Base/Perspex.Base.csproj

@@ -38,6 +38,7 @@
     <Compile Include="Contract.cs" />
     <Compile Include="IDescription.cs" />
     <Compile Include="IObservableDescription.cs" />
+    <Compile Include="IReadOnlyPerspexList.cs" />
     <Compile Include="PerspexList.cs" />
     <Compile Include="PerspexObject.cs" />
     <Compile Include="PerspexProperty.cs" />

Perspex.Base/PerspexList.cs

@@ -7,44 +7,252 @@
 namespace Perspex
 {
     using System;
+    using System.Collections;
     using System.Collections.Generic;
-    using System.Collections.ObjectModel;
     using System.Collections.Specialized;
-    using System.Reactive.Linq;
+    using System.ComponentModel;
+    using System.Linq;
 
-    public class PerspexList<T> : ObservableCollection<T>
+    public class PerspexList<T> : IList<T>, IList, IReadOnlyPerspexList<T>, INotifyCollectionChanged, INotifyPropertyChanged
     {
+        private List<T> inner;
+
         public PerspexList()
+            : this(Enumerable.Empty<T>())
         {
-            this.Initialize();
         }
 
         public PerspexList(IEnumerable<T> items)
-            : base(items)
         {
-            this.Initialize();
+            this.inner = new List<T>(items);
+        }
+
+        public event NotifyCollectionChangedEventHandler CollectionChanged;
+
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        public T this[int index]
+        {
+            get
+            {
+                return this.inner[index];
+            }
+
+            set
+            {
+                T old = this.inner[index];
+                this.inner[index] = value;
+
+                if (this.CollectionChanged != null)
+                {
+                    var e = new NotifyCollectionChangedEventArgs(
+                        NotifyCollectionChangedAction.Replace,
+                        value,
+                        old);
+                    this.CollectionChanged(this, e);
+                }
+            }
+        }
+
+        public int Count
+        {
+            get { return this.inner.Count; }
+        }
+
+        public bool IsReadOnly
+        {
+            get { return false; }
+        }
+
+        bool IList.IsFixedSize
+        {
+            get { return false; }
+       }
+
+        bool IList.IsReadOnly
+        {
+            get { return false; }
         }
 
-        public IObservable<NotifyCollectionChangedEventArgs> Changed
+        object IList.this[int index]
         {
-            get;
-            private set;
+            get { return this[index]; }
+
+            set { this[index] = (T)value; }
+        }
+
+        int ICollection.Count
+        {
+            get { return this.inner.Count; }
+        }
+
+        bool ICollection.IsSynchronized
+        {
+            get { return false; }
+        }
+
+        object ICollection.SyncRoot
+        {
+            get { return null; }
+        }
+
+        public void Add(T item)
+        {
+            int index = this.inner.Count;
+            this.inner.Add(item);
+            this.NotifyAdd(new[] { item });
         }
 
         public void AddRange(IEnumerable<T> items)
         {
-            foreach (T item in items)
+            int index = this.inner.Count;
+            this.inner.AddRange(items);
+            this.NotifyAdd((items as IList) ?? items.ToList());
+        }
+
+        public void Clear()
+        {
+            var old = this.inner;
+            this.inner = new List<T>();
+            this.NotifyRemove(old);
+        }
+
+        public bool Contains(T item)
+        {
+            return this.inner.Contains(item);
+        }
+
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            this.inner.CopyTo(array, arrayIndex);
+        }
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            return this.inner.GetEnumerator();
+        }
+
+        public int IndexOf(T item)
+        {
+            return this.inner.IndexOf(item);
+        }
+
+        public void Insert(int index, T item)
+        {
+            this.inner.Insert(index, item);
+            this.NotifyAdd(new[] { item });
+        }
+
+        public void InsertRange(int index, IEnumerable<T> items)
+        {
+            this.inner.InsertRange(index, items);
+            this.NotifyAdd((items as IList) ?? items.ToList());
+        }
+
+        public bool Remove(T item)
+        {
+            bool result = this.inner.Remove(item);
+            this.NotifyRemove(new[] { item });
+            return result;
+        }
+
+        public void RemoveAll(IEnumerable<T> items)
+        {
+            List<T> removed = new List<T>();
+
+            foreach (var i in items)
+            {
+                if (this.inner.Remove(i))
+                {
+                    removed.Add(i);
+                }
+            }
+
+            this.NotifyRemove(removed);
+        }
+
+        public void RemoveAt(int index)
+        {
+            T item = this.inner[index];
+            this.inner.RemoveAt(index);
+            this.NotifyRemove(new[] { item });
+        }
+
+        int IList.Add(object value)
+        {
+            int index = this.Count;
+            this.Add((T)value);
+            return index;
+        }
+
+        bool IList.Contains(object value)
+        {
+            return this.Contains((T)value);
+        }
+
+        void IList.Clear()
+        {
+            this.Clear();
+        }
+
+        int IList.IndexOf(object value)
+        {
+            return this.IndexOf((T)value);
+        }
+
+        void IList.Insert(int index, object value)
+        {
+            this.Insert(index, (T)value);
+        }
+
+        void IList.Remove(object value)
+        {
+            this.Remove((T)value);
+        }
+
+        void IList.RemoveAt(int index)
+        {
+            this.RemoveAt(index);
+        }
+
+        void ICollection.CopyTo(Array array, int index)
+        {
+            this.inner.CopyTo((T[])array, index);
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return this.inner.GetEnumerator();
+        }
+
+        private void NotifyAdd(IList t)
+        {
+            if (this.CollectionChanged != null)
             {
-                this.Add(item);
+                var e = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, t);
+                this.CollectionChanged(this, e);
             }
+
+            this.NotifyCountChanged();
         }
 
-        private void Initialize()
+        private void NotifyCountChanged()
         {
-            this.Changed = Observable.FromEvent<NotifyCollectionChangedEventHandler, NotifyCollectionChangedEventArgs>(
-                handler => (sender, e) => handler(e),
-                handler => this.CollectionChanged += handler,
-                handler => this.CollectionChanged -= handler);
+            if (this.PropertyChanged != null)
+            {
+                this.PropertyChanged(this, new PropertyChangedEventArgs("Count"));
+            }
+        }
+
+        private void NotifyRemove(IList t)
+        {
+            if (this.CollectionChanged != null)
+            {
+                var e = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, t);
+                this.CollectionChanged(this, e);
+            }
+
+            this.NotifyCountChanged();
         }
     }
 }

Perspex.Controls/Control.cs

@@ -188,53 +188,5 @@ namespace Perspex.Controls
                 }
             });
         }
-
-        protected virtual DataTemplate FindDataTemplate(object content)
-        {
-            // TODO: This needs to traverse the logical tree, not the visual.
-            foreach (var i in this.GetSelfAndVisualAncestors().OfType<Control>())
-            {
-                foreach (DataTemplate dt in i.DataTemplates.Reverse())
-                {
-                    if (dt.Match(content))
-                    {
-                        return dt;
-                    }
-                }
-            }
-
-            IGlobalDataTemplates global = Locator.Current.GetService<IGlobalDataTemplates>();
-
-            if (global != null)
-            {
-                foreach (DataTemplate dt in global.DataTemplates.Reverse())
-                {
-                    if (dt.Match(content))
-                    {
-                        return dt;
-                    }
-                }
-            }
-
-            return null;
-        }
-
-        protected Control ApplyDataTemplate(object content)
-        {
-            DataTemplate result = this.FindDataTemplate(content);
-
-            if (result != null)
-            {
-                return result.Build(content);
-            }
-            else if (content is Control)
-            {
-                return (Control)content;
-            }
-            else
-            {
-                return DataTemplate.Default.Build(content);
-            }
-        }
     }
 }

Perspex.Controls/DataTemplateExtensions.cs

@@ -0,0 +1,62 @@
+// -----------------------------------------------------------------------
+// <copyright file="DataTemplateExtensions.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Controls
+{
+    using System.Linq;
+    using Splat;
+
+    public static class DataTemplateExtensions
+    {
+        public static Control ApplyDataTemplate(this Control control, object data)
+        {
+            DataTemplate result = control.FindDataTemplate(data);
+
+            if (result != null)
+            {
+                return result.Build(data);
+            }
+            else if (data is Control)
+            {
+                return (Control)data;
+            }
+            else
+            {
+                return DataTemplate.Default.Build(data);
+            }
+        }
+
+        public static DataTemplate FindDataTemplate(this Control control, object data)
+        {
+            // TODO: This needs to traverse the logical tree, not the visual.
+            foreach (var i in control.GetSelfAndVisualAncestors().OfType<Control>())
+            {
+                foreach (DataTemplate dt in i.DataTemplates.Reverse())
+                {
+                    if (dt.Match(data))
+                    {
+                        return dt;
+                    }
+                }
+            }
+
+            IGlobalDataTemplates global = Locator.Current.GetService<IGlobalDataTemplates>();
+
+            if (global != null)
+            {
+                foreach (DataTemplate dt in global.DataTemplates.Reverse())
+                {
+                    if (dt.Match(data))
+                    {
+                        return dt;
+                    }
+                }
+            }
+
+            return null;
+        }
+    }
+}

Perspex.Controls/Generators/IItemContainerGenerator.cs

@@ -0,0 +1,38 @@
+// -----------------------------------------------------------------------
+// <copyright file="IItemContainerGenerator.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Controls.Generators
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+
+    public enum ItemContainerGeneratorState
+    {
+        NoStarted,
+        Generating,
+        Generated,
+    }
+
+    public interface IItemContainerGenerator
+    {
+        event EventHandler StateChanged;
+
+        ItemContainerGeneratorState State { get; }
+
+        Control GetContainerForItem(object item);
+
+        object GetItemForContainer(Control container);
+
+        IEnumerable<Tuple<object, Control>> GetAll();
+
+        IEnumerable<Control> Generate(IEnumerable items);
+
+        IEnumerable<Control> Remove(IEnumerable item);
+
+        void RemoveAll();
+    }
+}

Perspex.Controls/Generators/ItemContainerGenerator.cs

@@ -0,0 +1,126 @@
+// -----------------------------------------------------------------------
+// <copyright file="ItemContainerGenerator.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Controls.Generators
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+    using System.Linq;
+
+    public class ItemContainerGenerator : IItemContainerGenerator
+    {
+        private Dictionary<object, Control> containersByItem = new Dictionary<object, Control>();
+
+        private Dictionary<Control, object> itemsByContainer = new Dictionary<Control, object>();
+
+        private ItemContainerGeneratorState state;
+
+        public ItemContainerGenerator(ItemsControl owner)
+        {
+            this.Owner = owner;
+        }
+
+        public event EventHandler StateChanged;
+
+        public ItemContainerGeneratorState State
+        {
+            get
+            {
+                return this.state;
+            }
+
+            set
+            {
+                if (this.state != value)
+                {
+                    this.state = value;
+
+                    if (this.StateChanged != null)
+                    {
+                        this.StateChanged(this, EventArgs.Empty);
+                    }
+                }
+            }
+        }
+
+        protected ItemsControl Owner
+        {
+            get;
+            private set;
+        }
+
+        public Control GetContainerForItem(object item)
+        {
+            Control result;
+            this.containersByItem.TryGetValue(item, out result);
+            return result;
+        }
+
+        public object GetItemForContainer(Control container)
+        {
+            object result;
+            this.itemsByContainer.TryGetValue(container, out result);
+            return result;
+        }
+
+        public IEnumerable<Tuple<object, Control>> GetAll()
+        {
+            return this.containersByItem.Select(x => Tuple.Create(x.Key, x.Value));
+        }
+
+        IEnumerable<Control> IItemContainerGenerator.Generate(IEnumerable items)
+        {
+            List<Control> result = new List<Control>();
+
+            this.State = ItemContainerGeneratorState.Generating;
+
+            try
+            {
+                foreach (object item in items)
+                {
+                    Control container = this.CreateContainerOverride(item);
+                    container.TemplatedParent = null;
+                    this.containersByItem.Add(item, container);
+                    this.itemsByContainer.Add(container, item);
+                    result.Add(container);
+                }
+            }
+            finally
+            {
+                this.State = ItemContainerGeneratorState.Generated;
+            }
+
+            return result;
+        }
+
+        IEnumerable<Control> IItemContainerGenerator.Remove(IEnumerable items)
+        {
+            List<Control> result = new List<Control>();
+
+            foreach (var item in items)
+            {
+                Control container = this.containersByItem[item];
+                this.containersByItem.Remove(item);
+                this.itemsByContainer.Remove(container);
+                result.Add(container);
+            }
+
+            return result;
+        }
+
+        void IItemContainerGenerator.RemoveAll()
+        {
+            this.containersByItem.Clear();
+            this.itemsByContainer.Clear();
+        }
+
+        protected virtual Control CreateContainerOverride(object item)
+        {
+            return this.Owner.ApplyDataTemplate(item);
+        }
+    }
+}

Perspex.Controls/Generators/TreeItemContainerGenerator.cs

@@ -0,0 +1,56 @@
+// -----------------------------------------------------------------------
+// <copyright file="TreeItemContainerGenerator.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Controls.Generators
+{
+    public class TreeItemContainerGenerator<T> : ItemContainerGenerator where T : TreeViewItem, new()
+    {
+        public TreeItemContainerGenerator(ItemsControl owner)
+            : base(owner)
+        {
+        }
+
+        protected override Control CreateContainerOverride(object item)
+        {
+            T result = item as T;
+
+            if (result == null)
+            {
+                TreeDataTemplate template = this.GetTreeDataTemplate(item);
+
+                System.Diagnostics.Debug.WriteLine("{0} created item for {1}", this.GetHashCode(), item);
+
+                result = new T
+                {
+                    Header = template.Build(item),
+                    Items = template.ItemsSelector(item),
+                    IsExpanded = template.IsExpanded(item),
+                };
+            }
+
+            return result;
+        }
+
+        private TreeDataTemplate GetTreeDataTemplate(object item)
+        {
+            DataTemplate template = this.Owner.FindDataTemplate(item);
+
+            if (template == null)
+            {
+                template = DataTemplate.Default;
+            }
+
+            TreeDataTemplate treeTemplate = template as TreeDataTemplate;
+
+            if (treeTemplate == null)
+            {
+                treeTemplate = new TreeDataTemplate(template.Build, x => null);
+            }
+
+            return treeTemplate;
+        }
+    }
+}

Perspex.Controls/Generators/TypedItemContainerGenerator.cs

@@ -0,0 +1,29 @@
+// -----------------------------------------------------------------------
+// <copyright file="TypedItemContainerGenerator.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Controls.Generators
+{
+    public class TypedItemContainerGenerator<T> : ItemContainerGenerator where T : ContentControl, new()
+    {
+        public TypedItemContainerGenerator(ItemsControl owner)
+            : base(owner)
+        {
+        }
+
+        protected override Control CreateContainerOverride(object item)
+        {
+            T result = item as T;
+
+            if (result == null)
+            {
+                result = new T();
+                result.Content = this.Owner.ApplyDataTemplate(item);
+            }
+
+            return result;
+        }
+    }
+}

Perspex.Controls/ItemsControl.cs

@@ -8,10 +8,9 @@ namespace Perspex.Controls
 {
     using System;
     using System.Collections;
-    using System.Collections.Generic;
-    using System.Collections.Specialized;
     using System.ComponentModel;
     using System.Linq;
+    using Perspex.Controls.Generators;
 
     public class ItemsControl : TemplatedControl
     {
@@ -24,73 +23,41 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<ItemsPanelTemplate> ItemsPanelProperty =
             PerspexProperty.Register<ItemsControl, ItemsPanelTemplate>("ItemsPanel", defaultValue: DefaultPanel);
 
-        private Dictionary<object, Control> controlsByItem = new Dictionary<object, Control>();
-
-        private Dictionary<Control, object> itemsByControl = new Dictionary<Control, object>();
+        private ItemContainerGenerator itemContainerGenerator;
 
         public ItemsControl()
         {
             this.GetObservableWithHistory(ItemsProperty).Subscribe(this.ItemsChanged);
         }
 
-        public IEnumerable Items
+        public ItemContainerGenerator ItemContainerGenerator
         {
-            get { return this.GetValue(ItemsProperty); }
-            set { this.SetValue(ItemsProperty, value); }
-        }
-
-        public ItemsPanelTemplate ItemsPanel
-        {
-            get { return this.GetValue(ItemsPanelProperty); }
-            set { this.SetValue(ItemsPanelProperty, value); }
-        }
-
-        public Control GetControlForItem(object item)
-        {
-            Control result;
-            this.controlsByItem.TryGetValue(item, out result);
-            return result;
-        }
-
-        public object GetItemForControl(Control control)
-        {
-            object result;
-            this.itemsByControl.TryGetValue(control, out result);
-            return result;
-        }
-
-        public IEnumerable<Control> GetAllItemControls()
-        {
-            return this.controlsByItem.Values;
-        }
+            get
+            {
+                if (this.itemContainerGenerator == null)
+                {
+                    this.itemContainerGenerator = this.CreateItemContainerGenerator();
+                }
 
-        internal Control CreateItemControl(object item)
-        {
-            Control control = this.CreateItemControlOverride(item);
-            this.itemsByControl.Add(control, item);
-            this.controlsByItem.Add(item, control);
-            return control;
+                return this.itemContainerGenerator;
+            }
         }
 
-        internal void RemoveItemControls(IEnumerable items)
+        protected virtual ItemContainerGenerator CreateItemContainerGenerator()
         {
-            foreach (object i in items)
-            {
-                Control control = this.GetControlForItem(i);
-                this.controlsByItem.Remove(i);
-                this.itemsByControl.Remove(control);
-            }
+            return new ItemContainerGenerator(this);
         }
 
-        internal void ClearItemControls()
+        public IEnumerable Items
         {
-            this.controlsByItem.Clear();
-            this.itemsByControl.Clear();
+            get { return this.GetValue(ItemsProperty); }
+            set { this.SetValue(ItemsProperty, value); }
         }
 
-        protected virtual Control CreateItemControlOverride(object item)
+        public ItemsPanelTemplate ItemsPanel
         {
-            return this.ApplyDataTemplate(item);
+            get { return this.GetValue(ItemsPanelProperty); }
+            set { this.SetValue(ItemsPanelProperty, value); }
         }
 
         private void ItemsChanged(Tuple<IEnumerable, IEnumerable> value)

Perspex.Controls/ItemsPresenter.cs

@@ -8,9 +8,9 @@ namespace Perspex.Controls
 {
     using System;
     using System.Collections;
-    using System.Collections.Generic;
     using System.Collections.Specialized;
-    using System.Linq;
+    using System.Reactive.Linq;
+    using Perspex.Controls.Generators;
 
     public class ItemsPresenter : Control, IVisual
     {
@@ -24,7 +24,7 @@ namespace Perspex.Controls
 
         public ItemsPresenter()
         {
-            this.GetObservableWithHistory(ItemsProperty).Subscribe(this.ItemsChanged);
+            this.GetObservableWithHistory(ItemsProperty).Skip(1).Subscribe(this.ItemsChanged);
         }
 
         public IEnumerable Items
@@ -58,53 +58,16 @@ namespace Perspex.Controls
             this.ItemsChanged(Tuple.Create(default(IEnumerable), this.Items));
         }
 
-        private Control CreateItemControl(object item)
+        private IItemContainerGenerator GetGenerator()
         {
             ItemsControl i = this.TemplatedParent as ItemsControl;
 
-            if (i != null)
+            if (i == null)
             {
-                return i.CreateItemControl(item);
+                throw new InvalidOperationException("ItemsPresenter must be part of an ItemsControl template.");
             }
-            else
-            {
-                return this.ApplyDataTemplate(item);
-            }
-        }
-         
-        private IEnumerable<Control> CreateItemControls(IEnumerable items)
-        {
-            if (items != null)
-            {
-                return items
-                    .Cast<object>()
-                    .Select(x => this.CreateItemControl(x))
-                    .OfType<Control>();
-            }
-            else
-            {
-                return Enumerable.Empty<Control>();
-            }
-        }
-
-        private void ClearItemControls()
-        {
-            ItemsControl i = this.TemplatedParent as ItemsControl;
-
-            if (i != null)
-            {
-                i.ClearItemControls();
-            }
-        }
-
-        private void RemoveItemControls(IEnumerable items)
-        {
-            ItemsControl i = this.TemplatedParent as ItemsControl;
 
-            if (i != null)
-            {
-                i.RemoveItemControls(items);
-            }
+            return i.ItemContainerGenerator;
         }
 
         private Panel GetPanel()
@@ -119,8 +82,12 @@ namespace Perspex.Controls
 
         private void ItemsChanged(Tuple<IEnumerable, IEnumerable> value)
         {
+            var generator = this.GetGenerator();
+
             if (value.Item1 != null)
             {
+                this.panel.Children.RemoveAll(generator.Remove(value.Item1));
+
                 INotifyCollectionChanged incc = value.Item1 as INotifyCollectionChanged;
 
                 if (incc != null)
@@ -129,24 +96,18 @@ namespace Perspex.Controls
                 }
             }
 
-            this.ClearItemControls();
-
             if (this.panel != null)
             {
-                var controls = this.CreateItemControls(value.Item2).ToList();
-
-                foreach (var control in controls)
+                if (value.Item2 != null)
                 {
-                    control.TemplatedParent = null;
-                }
+                    this.panel.Children.AddRange(generator.Generate(this.Items));
 
-                this.panel.Children = new Controls(controls);
+                    INotifyCollectionChanged incc = value.Item2 as INotifyCollectionChanged;
 
-                INotifyCollectionChanged incc = value.Item2 as INotifyCollectionChanged;
-
-                if (incc != null)
-                {
-                    incc.CollectionChanged += this.ItemsCollectionChanged;
+                    if (incc != null)
+                    {
+                        incc.CollectionChanged += this.ItemsCollectionChanged;
+                    }
                 }
             }
         }
@@ -155,28 +116,21 @@ namespace Perspex.Controls
         {
             if (this.panel != null)
             {
-                // TODO: Handle Move and Replace.
+                var generator = this.GetGenerator();
+
+                // TODO: Handle Move and Replace etc.
                 switch (e.Action)
                 {
                     case NotifyCollectionChangedAction.Add:
-                        var controls = this.CreateItemControls(e.NewItems).ToList();
-
-                        foreach (var control in controls)
-                        {
-                            control.TemplatedParent = null;
-                        }
-
-                        this.panel.Children.AddRange(controls);
+                        this.panel.Children.AddRange(generator.Generate(e.NewItems));
                         break;
 
                     case NotifyCollectionChangedAction.Remove:
-                        this.RemoveItemControls(e.OldItems);
-                        break;
-                        
-                    case NotifyCollectionChangedAction.Reset:
-                        this.ItemsChanged(Tuple.Create(this.Items, this.Items));
+                        this.panel.Children.RemoveAll(generator.Remove(e.OldItems));
                         break;
                 }
+
+                this.InvalidateMeasure();
             }
         }
     }

Perspex.Controls/Perspex.Controls.csproj

@@ -45,7 +45,11 @@
     <Compile Include="ControlExtensions.cs" />
     <Compile Include="Controls.cs" />
     <Compile Include="ControlTemplate.cs" />
+    <Compile Include="DataTemplateExtensions.cs" />
     <Compile Include="DataTemplate.cs" />
+    <Compile Include="Generators\TreeItemContainerGenerator.cs" />
+    <Compile Include="Generators\TypedItemContainerGenerator.cs" />
+    <Compile Include="Generators\ItemContainerGenerator.cs" />
     <Compile Include="IGlobalDataTemplates.cs" />
     <Compile Include="DataTemplates.cs" />
     <Compile Include="Decorator.cs" />
@@ -56,6 +60,7 @@
     <Compile Include="HeaderedItemsControl.cs" />
     <Compile Include="IHeadered.cs" />
     <Compile Include="Image.cs" />
+    <Compile Include="Generators\IItemContainerGenerator.cs" />
     <Compile Include="ItemsControl.cs" />
     <Compile Include="ItemsPanelTemplate.cs" />
     <Compile Include="ItemsPresenter.cs" />

Perspex.Controls/TabControl.cs

@@ -7,9 +7,9 @@
 namespace Perspex.Controls
 {
     using System;
-    using System.Collections.Generic;
     using System.Linq;
     using System.Reactive.Linq;
+    using Perspex.Controls.Generators;
 
     public class TabControl : SelectingItemsControl
     {
@@ -20,43 +20,23 @@ namespace Perspex.Controls
 
         public TabControl()
         {
-            this.GetObservable(SelectedItemProperty).Skip(1).Subscribe(this.SelectedItemChanged);
+            this.GetObservable(SelectedItemProperty).Subscribe(x =>
+            {
+                ContentControl c = x as ContentControl;
+                object content = (c != null) ? c.Content : null;
+                this.SetValue(SelectedContentProperty, content);
+            });
         }
 
-        protected override void OnTemplateApplied()
+        protected override ItemContainerGenerator CreateItemContainerGenerator()
         {
-            this.tabStrip = this.GetTemplateControls()
-                .OfType<TabStrip>()
-                .FirstOrDefault();
-
-            if (this.tabStrip != null)
-            {
-                if (this.IsSet(SelectedItemProperty))
-                {
-                    this.SelectedItem = SelectedItem;
-                }
-
-                this.tabStrip.GetObservable(TabStrip.SelectedItemProperty).Subscribe(x =>
-                {
-                    this.SelectedItem = x;
-                });
-            }
+            return new TypedItemContainerGenerator<TabItem>(this);
         }
 
-        private void SelectedItemChanged(object item)
+        protected override void OnTemplateApplied()
         {
-            this.SelectedItem = item;
-
-            ContentControl content = item as ContentControl;
-
-            if (content != null)
-            {
-                this.SetValue(SelectedContentProperty, content.Content);
-            }
-            else
-            {
-                this.SetValue(SelectedContentProperty, item);
-            }
+            this.tabStrip = this.GetTemplateControls().OfType<TabStrip>().FirstOrDefault();
+            this.BindTwoWay(SelectedItemProperty, this.tabStrip, SelectedItemProperty);
         }
     }
 }

Perspex.Controls/TabStrip.cs

@@ -9,6 +9,7 @@ namespace Perspex.Controls
     using System;
     using System.Collections;
     using System.Linq;
+    using Perspex.Controls.Generators;
     using Perspex.Input;
 
     public class TabStrip : SelectingItemsControl
@@ -24,38 +25,38 @@ namespace Perspex.Controls
         public TabStrip()
         {
             this.PointerPressed += this.OnPointerPressed;
-            this.GetObservable(ItemsProperty).Subscribe(this.ItemsChanged);
             this.GetObservable(SelectedItemProperty).Subscribe(this.SelectedItemChanged);
         }
 
-        protected override Control CreateItemControlOverride(object item)
+        protected override ItemContainerGenerator CreateItemContainerGenerator()
         {
-            TabItem result = item as TabItem;
+            TabControl tabControl = this.TemplatedParent as TabControl;
+            ItemContainerGenerator result;
 
-            if (result == null)
+            if (tabControl != null)
             {
-                result = new TabItem
-                {
-                    Content = this.ApplyDataTemplate(item),
-                };
+                result = tabControl.ItemContainerGenerator;
+            }
+            else
+            {
+                result = new TypedItemContainerGenerator<TabItem>(this);
             }
 
-            result.IsSelected = this.SelectedItem == item;
+            result.StateChanged += ItemsContainerGeneratorStateChanged;
 
             return result;
         }
 
-        private void ItemsChanged(IEnumerable items)
+        private void ItemsContainerGeneratorStateChanged(object sender, EventArgs e)
         {
-            if (items != null)
+            if (this.ItemContainerGenerator.State == ItemContainerGeneratorState.Generated)
             {
-                this.SelectedItem =
-                    items.OfType<TabItem>().FirstOrDefault(x => x.IsSelected) ??
-                    items.OfType<object>().FirstOrDefault();
-            }
-            else
-            {
-                this.SelectedItem = null;
+                var tabs = this.ItemContainerGenerator.GetAll()
+                    .Select(x => x.Item2)
+                    .OfType<TabItem>()
+                    .ToList();
+
+                this.SelectedItem = tabs.FirstOrDefault(x => x.IsSelected) ?? tabs.FirstOrDefault();
             }
         }
 
@@ -77,11 +78,11 @@ namespace Perspex.Controls
             }
         }
 
-        private void SelectedItemChanged(object selectedItem)
+        private void SelectedItemChanged(object selected)
         {
-            foreach (TabItem item in this.GetAllItemControls())
+            foreach (TabItem item in this.ItemContainerGenerator.GetAll().Select(x => x.Item2))
             {
-                item.IsSelected = item == selectedItem;
+                item.IsSelected = selected == item;
             }
         }
     }

Perspex.Controls/TreeView.cs

@@ -10,6 +10,7 @@ namespace Perspex.Controls
     using System.Collections;
     using System.Linq;
     using System.Reactive.Linq;
+    using Perspex.Controls.Generators;
     using Perspex.Input;
 
     public class TreeView : SelectingItemsControl
@@ -19,42 +20,9 @@ namespace Perspex.Controls
             this.PointerPressed += this.OnPointerPressed;
         }
 
-        protected override Control CreateItemControlOverride(object item)
+        protected override ItemContainerGenerator CreateItemContainerGenerator()
         {
-            TreeViewItem result = item as TreeViewItem;
-
-            if (result == null)
-            {
-                TreeDataTemplate template = this.GetTreeDataTemplate(item);
-
-                result = new TreeViewItem
-                {
-                    Header = template.Build(item),
-                    Items = template.ItemsSelector(item),
-                    IsExpanded = template.IsExpanded(item),
-                };
-            }
-
-            return result;
-        }
-
-        private TreeDataTemplate GetTreeDataTemplate(object item)
-        {
-            DataTemplate template = this.FindDataTemplate(item);
-
-            if (template == null)
-            {
-                template = DataTemplate.Default;
-            }
-
-            TreeDataTemplate treeTemplate = template as TreeDataTemplate;
-
-            if (treeTemplate == null)
-            {
-                treeTemplate = new TreeDataTemplate(template.Build, x => null);
-            }
-
-            return treeTemplate;
+            return new TreeItemContainerGenerator<TreeViewItem>(this);
         }
 
         private void OnPointerPressed(object sender, PointerEventArgs e)
@@ -75,7 +43,7 @@ namespace Perspex.Controls
                         i.IsSelected = i == item;
                     }
 
-                    this.SelectedItem = this.GetItemForControl(item);
+                    this.SelectedItem = this.ItemContainerGenerator.GetContainerForItem(item);
                 }
             }
 

Perspex.Controls/TreeViewItem.cs

@@ -8,6 +8,7 @@ namespace Perspex.Controls
 {
     using System;
     using System.Linq;
+    using Perspex.Controls.Generators;
 
     public class TreeViewItem : HeaderedItemsControl
     {
@@ -17,7 +18,7 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<bool> IsSelectedProperty =
             PerspexProperty.Register<TreeViewItem, bool>("IsSelected");
 
-        TreeView parent;
+        TreeView treeView;
 
         public TreeViewItem()
         {
@@ -37,21 +38,33 @@ namespace Perspex.Controls
             set { this.SetValue(IsSelectedProperty, value); }
         }
 
-        protected override Control CreateItemControlOverride(object item)
+        protected override ItemContainerGenerator CreateItemContainerGenerator()
         {
-            if (this.parent != null)
+            if (this.treeView == null)
             {
-                return this.parent.CreateItemControl(item);
-            }
-            else
-            {
-                throw new InvalidOperationException("TreeViewItem must be added to TreeView.");
+                throw new InvalidOperationException(
+                    "Cannot get the ItemContainerGenerator for a TreeViewItem " + 
+                    "before it is added to a TreeView.");
             }
+
+            return this.treeView.ItemContainerGenerator;
         }
 
         protected override void OnVisualParentChanged(Visual oldParent)
         {
-            this.parent = this.GetVisualAncestors().OfType<TreeView>().FirstOrDefault();
+            if (this.GetVisualParent() != null)
+            {
+                this.treeView = this.GetVisualAncestors().OfType<TreeView>().FirstOrDefault();
+
+                if (this.treeView == null)
+                {
+                    throw new InvalidOperationException("TreeViewItems must be added to a TreeView.");
+                }
+            }
+            else
+            {
+                this.treeView = null;
+            }
         }
     }
 }

Perspex.SceneGraph/IVisual.cs

@@ -51,7 +51,7 @@ namespace Perspex
         /// <summary>
         /// Gets the scene graph node's child nodes.
         /// </summary>
-        IEnumerable<IVisual> VisualChildren { get; }
+        IReadOnlyPerspexList<IVisual> VisualChildren { get; }
 
         /// <summary>
         /// Gets the scene graph node's parent node.

Perspex.SceneGraph/Visual.cs

@@ -30,7 +30,7 @@ namespace Perspex
 
         private Rect bounds;
 
-        private PerspexList<Visual> visualChildren;
+        private PerspexList<IVisual> visualChildren;
 
         private Visual visualParent;
 
@@ -68,7 +68,7 @@ namespace Perspex
             get { return this.bounds; }
         }
 
-        IEnumerable<IVisual> IVisual.VisualChildren
+        IReadOnlyPerspexList<IVisual> IVisual.VisualChildren
         {
             get
             {
@@ -190,7 +190,7 @@ namespace Perspex
         {
             if (this.visualChildren == null)
             {
-                this.visualChildren = new PerspexList<Visual>();
+                this.visualChildren = new PerspexList<IVisual>();
                 this.visualChildren.CollectionChanged += VisualChildrenChanged;
                 this.CreateVisualChildren();
             }

TestApplication/Program.cs

@@ -195,24 +195,6 @@ namespace TestApplication
                                         Id = "treeView",
                                         Items = treeData,
                                     },
-                                    new StackPanel
-                                    {
-                                        Orientation = Orientation.Vertical,
-                                        Gap = 2.0,
-                                        Children = new Controls
-                                        {
-                                            new TextBox
-                                            {
-                                                Id = "newTreeViewItemText",
-                                                Text = "New Item"
-                                            },
-                                            new Button
-                                            {
-                                                Id = "addTreeViewItem",
-                                                Content = "Add",
-                                            },
-                                        }
-                                    },
                                 }
                             },
                         },
@@ -220,21 +202,6 @@ namespace TestApplication
                 }
             };
 
-            //var treeView = window.FindControl<TreeView>("treeView");
-            //var newTreeViewItemText = window.FindControl<TextBox>("newTreeViewItemText");
-            //var addTreeViewItem = window.FindControl<Button>("addTreeViewItem");
-
-            //addTreeViewItem.Click += (s, e) =>
-            //{
-            //    if (treeView.SelectedItem != null)
-            //    {
-            //        ((Node)treeView.SelectedItem).Children.Add(new Node
-            //        {
-            //            Name = newTreeViewItemText.Text,
-            //        });
-            //    }
-            //};
-
             window.Show();
             Application.Current.Run(window);
         }