Added Layoutable.ApplyTemplate.

Rather than each different presenter/templated control rolling their
own.

Perspex.Controls/Presenters/ContentPresenter.cs

@@ -30,23 +30,21 @@ namespace Perspex.Controls.Presenters
             set { this.SetValue(ContentProperty, value); }
         }
 
-        protected override Size MeasureCore(Size availableSize)
+        protected override sealed void ApplyTemplate()
         {
             if (!this.createdChild)
             {
                 this.CreateChild();
             }
+        }
 
+        protected override Size MeasureCore(Size availableSize)
+        {
             return base.MeasureCore(availableSize);
         }
 
         protected override Size MeasureOverride(Size availableSize)
         {
-            if (!this.createdChild)
-            {
-                this.CreateChild();
-            }
-
             Control child = ((IVisual)this).VisualChildren.SingleOrDefault() as Control;
 
             if (child != null)

Perspex.Controls/Presenters/ItemsPresenter.cs

@@ -41,13 +41,16 @@ namespace Perspex.Controls.Presenters
             set { this.SetValue(ItemsPanelProperty, value); }
         }
 
-        protected override Size MeasureOverride(Size availableSize)
+        protected override sealed void ApplyTemplate()
         {
             if (!this.createdPanel)
             {
                 this.CreatePanel();
             }
+        }
 
+        protected override Size MeasureOverride(Size availableSize)
+        {
             panel.Measure(availableSize);
             return panel.DesiredSize.Value;
         }

Perspex.Controls/Primitives/TemplatedControl.cs

@@ -30,6 +30,28 @@ namespace Perspex.Controls.Primitives
         {
         }
 
+        protected sealed override void ApplyTemplate()
+        {
+            if (!this.templateApplied)
+            {
+                this.ClearVisualChildren();
+
+                if (this.Template != null)
+                {
+                    this.Log().Debug(
+                        "Creating template for {0} (#{1:x8})",
+                        this.GetType().Name,
+                        this.GetHashCode());
+
+                    var child = this.Template.Build(this);
+                    this.AddVisualChild(child);
+                    this.OnTemplateApplied();
+                }
+
+                this.templateApplied = true;
+            }
+        }
+
         protected override Size ArrangeOverride(Size finalSize)
         {
             Control child = ((IVisual)this).VisualChildren.SingleOrDefault() as Control;
@@ -47,11 +69,6 @@ namespace Perspex.Controls.Primitives
 
         protected override Size MeasureOverride(Size availableSize)
         {
-            if (!this.templateApplied)
-            {
-                this.ApplyTemplate();
-            }
-
             Control child = ((IVisual)this).VisualChildren.SingleOrDefault() as Control;
 
             if (child != null)
@@ -86,24 +103,5 @@ namespace Perspex.Controls.Primitives
         protected virtual void OnTemplateApplied()
         {
         }
-
-        private void ApplyTemplate()
-        {
-            this.ClearVisualChildren();
-
-            if (this.Template != null)
-            {
-                this.Log().Debug(
-                    "Creating template for {0} (#{1:x8})",
-                    this.GetType().Name,
-                    this.GetHashCode());
-
-                var child = this.Template.Build(this);
-                this.AddVisualChild(child);
-                this.OnTemplateApplied();
-            }
-
-            this.templateApplied = true;
-        }
     }
 }

Perspex.Layout/Layoutable.cs

@@ -196,6 +196,10 @@ namespace Perspex.Layout
             property.Changed.Subscribe(AffectsMeasureInvalidate);
         }
 
+        protected virtual void ApplyTemplate()
+        {
+        }
+
         protected virtual void ArrangeCore(Rect finalRect)
         {
             if (this.IsVisible)
@@ -259,6 +263,8 @@ namespace Perspex.Layout
         {
             if (this.IsVisible)
             {
+                this.ApplyTemplate();
+
                 var constrained = LayoutHelper.ApplyLayoutConstraints(this, availableSize)
                     .Deflate(this.Margin);