Correctly apply nested templates.

When a templated control's template itself contains templated controls,
make sure all of the templates are applied, as the nested templated
control might contain something the top-most templated control is
looking for.

Perspex.Controls/ControlExtensions.cs

@@ -31,9 +31,9 @@ namespace Perspex.Controls
         {
             IVisual visual = parent as IVisual;
 
-            foreach (IVisual child in visual.VisualChildren.OfType<Control>().Where(x => x.TemplatedParent == templated))
+            foreach (var child in visual.VisualChildren.OfType<Control>().Where(x => x.TemplatedParent != null))
             {
-                yield return (Control)child;
+                yield return child;
 
                 foreach (IVisual grandchild in GetTemplateControls(templated, child))
                 {

Perspex.Controls/ControlTemplate.cs

@@ -7,6 +7,8 @@
 namespace Perspex.Controls
 {
     using System;
+    using System.Linq;
+    using Perspex.Layout;
     using Perspex.Styling;
 
     public class ControlTemplate

Perspex.Controls/Presenters/ContentPresenter.cs

@@ -30,7 +30,7 @@ namespace Perspex.Controls.Presenters
             set { this.SetValue(ContentProperty, value); }
         }
 
-        protected override sealed void ApplyTemplate()
+        public override sealed void ApplyTemplate()
         {
             if (!this.createdChild)
             {

Perspex.Controls/Presenters/ItemsPresenter.cs

@@ -41,7 +41,7 @@ namespace Perspex.Controls.Presenters
             set { this.SetValue(ItemsPanelProperty, value); }
         }
 
-        protected override sealed void ApplyTemplate()
+        public override sealed void ApplyTemplate()
         {
             if (!this.createdPanel)
             {

Perspex.Controls/Primitives/TemplatedControl.cs

@@ -20,6 +20,16 @@ namespace Perspex.Controls.Primitives
 
         private bool templateApplied;
 
+        static TemplatedControl()
+        {
+            TemplateProperty.Changed.Subscribe(e =>
+            {
+                var templatedControl = (TemplatedControl)e.Sender;
+                templatedControl.templateApplied = false;
+                templatedControl.InvalidateMeasure();
+            });
+        }
+
         public ControlTemplate Template
         {
             get { return this.GetValue(TemplateProperty); }
@@ -30,7 +40,7 @@ namespace Perspex.Controls.Primitives
         {
         }
 
-        protected override void ApplyTemplate()
+        public sealed override void ApplyTemplate()
         {
             if (!this.templateApplied)
             {
@@ -45,6 +55,17 @@ namespace Perspex.Controls.Primitives
 
                     var child = this.Template.Build(this);
                     this.AddVisualChild(child);
+
+                    var templateChildren = this.GetVisualDescendents()
+                        .OfType<Control>()
+                        .Where(x => x.TemplatedParent != null);
+
+                    foreach (var i in templateChildren)
+                    {
+                        i.ApplyTemplate();
+                    }
+
+
                     this.OnTemplateApplied();
                 }
 
@@ -82,7 +103,9 @@ namespace Perspex.Controls.Primitives
 
         protected T FindTemplateChild<T>(string id) where T : Control
         {
-            return this.GetTemplateControls().OfType<T>().FirstOrDefault(x => x.Id == id);
+            return this.GetTemplateControls()
+                .Where(x => x.TemplatedParent == this)
+                .OfType<T>().FirstOrDefault(x => x.Id == id);
         }
 
         protected T GetTemplateChild<T>(string id) where T : Control

Perspex.Controls/TextBox.cs

@@ -141,17 +141,7 @@ namespace Perspex.Controls
 
         protected override void OnTemplateApplied()
         {
-            Decorator textContainer = this.GetVisualDescendents()
-                .OfType<Decorator>()
-                .FirstOrDefault(x => x.Id == "textContainer");
-
-            if (textContainer == null)
-            {
-                throw new Exception(
-                    "TextBox template doesn't contain a textContainer " +
-                    "or textContainer is not a Decorator.");
-            }
-
+            Decorator textContainer = this.GetTemplateChild<Decorator>("textContainer");
             textContainer.Content = this.textBoxView = new TextBoxView(this);
         }
 

Perspex.Layout/Layoutable.cs

@@ -163,6 +163,10 @@ namespace Perspex.Layout
             get { return this.previousArrange; }
         }
 
+        public virtual void ApplyTemplate()
+        {
+        }
+
         public void Measure(Size availableSize, bool force = false)
         {
             if (double.IsNaN(availableSize.Width) || double.IsNaN(availableSize.Height))
@@ -259,10 +263,6 @@ namespace Perspex.Layout
             property.Changed.Subscribe(AffectsMeasureInvalidate);
         }
 
-        protected virtual void ApplyTemplate()
-        {
-        }
-
         protected virtual void ArrangeCore(Rect finalRect)
         {
             if (this.IsVisible)