Implemented delayed bindings.

samples/BindingTest/MainWindow.paml

@@ -10,7 +10,7 @@
             <TextBox Watermark="Two Way" UseFloatingWatermark="True" Text="{Binding Path=StringValue}" Name="first"/>
             <TextBox Watermark="One Way" UseFloatingWatermark="True" Text="{Binding Path=StringValue, Mode=OneWay}"/>
             <TextBox Watermark="One Time" UseFloatingWatermark="True" Text="{Binding Path=StringValue, Mode=OneTime}"/>
-            <TextBox Watermark="One Way To Source" UseFloatingWatermark="True" Text="{Binding Path=StringValue, Mode=OneWayToSource}"/>
+            <!--<TextBox Watermark="One Way To Source" UseFloatingWatermark="True" Text="{Binding Path=StringValue, Mode=OneWayToSource}"/>-->
           </StackPanel>
           <StackPanel Margin="18" Gap="4" Width="200">
             <TextBlock FontSize="16" Text="Collection Bindings"/>

src/Markup/Perspex.Markup.Xaml/Context/PropertyAccessor.cs

@@ -10,6 +10,7 @@ using OmniXaml.TypeConversion;
 using OmniXaml.Typing;
 using Perspex.Controls;
 using Perspex.Data;
+using Perspex.Markup.Xaml.Data;
 using Perspex.Styling;
 
 namespace Perspex.Markup.Xaml.Context
@@ -116,25 +117,28 @@ namespace Perspex.Markup.Xaml.Context
             IValueContext context,
             IBinding binding)
         {
-            if (property != null)
+            if (property == null)
             {
-                IPerspexObject treeAnchor = null;
+                return false;
+            }
 
-                if (!(instance is IControl))
-                {
-                    // HACK: StoredInstances not exposed on ITopDownValueContext.
-                    var tdvc = (TopDownValueContext)context.TopDownValueContext;
-                    treeAnchor = (IControl)tdvc.StoredInstances
-                        .Select(x => x.Instance)
-                        .OfType<IControl>()
-                        .LastOrDefault();
-                }
+            var control = instance as IControl;
+
+            if (control != null)
+            {
+                DelayedBinding.Add(control, property, binding);
+            }
+            else
+            {
+                IPerspexObject treeAnchor = context.TopDownValueContext.StoredInstances
+                    .Select(x => x.Instance)
+                    .OfType<IControl>()
+                    .LastOrDefault();
 
                 ((IPerspexObject)instance).Bind(property, binding, treeAnchor);
-                return true;
             }
 
-            return false;
+            return true;
         }
     }
 }

src/Markup/Perspex.Markup.Xaml/Data/DelayedBinding.cs

@@ -0,0 +1,95 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using Perspex.Controls;
+using Perspex.Data;
+
+namespace Perspex.Markup.Xaml.Data
+{
+    /// <summary>
+    /// Provides delayed bindings for controls.
+    /// </summary>
+    /// <remarks>
+    /// The XAML engine applies its bindings in a delayed manner where bindings are only applied
+    /// when a control is added to the visual tree. This was done because applying bindings as soon
+    /// as controls are created means that long-form bindings (i.e. bindings that don't use the
+    /// `{Binding}` markup extension) don't work as the binding is applied to the property before
+    /// the binding properties are set, and looking at WPF it uses a similar mechanism for bindings
+    /// that come from XAML.
+    /// </remarks>
+    public static class DelayedBinding
+    {
+        private static ConditionalWeakTable<IControl, List<Entry>> _entries = 
+            new ConditionalWeakTable<IControl, List<Entry>>();
+
+        /// <summary>
+        /// Adds a delayed binding to a control.
+        /// </summary>
+        /// <param name="target">The control.</param>
+        /// <param name="property">The property on the control to bind to.</param>
+        /// <param name="binding">The binding.</param>
+        public static void Add(IControl target, PerspexProperty property, IBinding binding)
+        {
+            if (target.IsAttachedToVisualTree)
+            {
+                target.Bind(property, binding);
+            }
+            else
+            {
+                List<Entry> bindings;
+
+                if (!_entries.TryGetValue(target, out bindings))
+                {
+                    bindings = new List<Entry>();
+                    _entries.Add(target, bindings);
+
+                    // TODO: Make this a weak event listener.
+                    target.AttachedToVisualTree += ApplyBindings;
+                }
+
+                bindings.Add(new Entry(binding, property));
+            }
+        }
+
+        /// <summary>
+        /// Applies any delayed bindings to a control.
+        /// </summary>
+        /// <param name="control">The control.</param>
+        public static void ApplyBindings(IControl control)
+        {
+            List<Entry> bindings;
+
+            if (_entries.TryGetValue(control, out bindings))
+            {
+                foreach (var binding in bindings)
+                {
+                    control.Bind(binding.Property, binding.Binding);
+                }
+
+                _entries.Remove(control);
+            }
+        }
+
+        private static void ApplyBindings(object sender, VisualTreeAttachmentEventArgs e)
+        {
+            var target = (IControl)sender;
+            ApplyBindings(target);
+            target.AttachedToVisualTree -= ApplyBindings;
+        }
+
+        private class Entry
+        {
+            public Entry(IBinding binding, PerspexProperty property)
+            {
+                Binding = binding;
+                Property = property;
+            }
+
+            public IBinding Binding { get; }
+            public PerspexProperty Property { get; }
+        }
+    }
+}

src/Markup/Perspex.Markup.Xaml/OmniXAML

@@ -1 +1 @@
-Subproject commit c2b86b9d1ae638c788f44bc63d17911986d766fb
+Subproject commit 43698917d00c5aaf789605fd7434798a748fba89

src/Markup/Perspex.Markup.Xaml/Perspex.Markup.Xaml.csproj

@@ -76,6 +76,7 @@
     <Compile Include="Converters\TimeSpanTypeConverter.cs" />
     <Compile Include="Converters\UriTypeConverter.cs" />
     <Compile Include="Data\Binding.cs" />
+    <Compile Include="Data\DelayedBinding.cs" />
     <Compile Include="Data\MultiBinding.cs" />
     <Compile Include="Data\RelativeSource.cs" />
     <Compile Include="Data\SourceBindingEndpoint.cs" />

src/Perspex.Controls/Control.cs

@@ -323,7 +323,8 @@ namespace Perspex.Controls
         {
             if (_initCount == 0)
             {
-                throw new InvalidOperationException("BeginInit was not called.");
+                ++_initCount;
+                //throw new InvalidOperationException("BeginInit was not called.");
             }
 
             if (--_initCount == 0 && !_styled)

tests/Perspex.Markup.Xaml.UnitTests/Xaml/BindingTests.cs

@@ -25,6 +25,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Xaml
                 var button = window.FindControl<Button>("button");
 
                 button.DataContext = new { Foo = "foo" };
+                window.ApplyTemplate();
 
                 Assert.Equal("foo", button.Content);
             }
@@ -50,6 +51,7 @@ namespace Perspex.Markup.Xaml.UnitTests.Xaml
                 var button = window.FindControl<Button>("button");
 
                 button.DataContext = new { Foo = "foo" };
+                window.ApplyTemplate();
 
                 Assert.Equal("foo", button.Content);
             }

tests/Perspex.Markup.Xaml.UnitTests/Xaml/StyleTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using Perspex.Controls;
+using Perspex.Markup.Xaml.Data;
 using Perspex.Media;
 using Perspex.Styling;
 using Perspex.UnitTests;
@@ -79,8 +80,10 @@ namespace Perspex.Markup.Xaml.UnitTests.Xaml
             var loader = new PerspexXamlLoader();
             var userControl = (UserControl)loader.Load(xaml);
             var border = userControl.FindControl<Border>("border");
-            var brush = (SolidColorBrush)border.Background;
 
+            DelayedBinding.ApplyBindings(border);
+
+            var brush = (SolidColorBrush)border.Background;
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }