Added hacky tab keyboard navigation.

This is a temporary workaround to #30 - it's very hacky:

- Tab key handling is built into TextBox - all other controls don't
work. It needs to be moved into InputElement.
- It only traverses siblings.
- Setting focus to template children is a hack.
- Many more problems.

Perspex.Controls/Presenters/TextPresenter.cs

@@ -286,6 +286,16 @@ namespace Perspex.Controls.Presenters
                     {
                         goto default;
                     }
+                    else if ((modifiers & ModifierKeys.Shift) == 0)
+                    {
+                        // TODO: Keyboard navigation should be moved to InputElement. This is just a 
+                        // hack to get TextBox tab navigation working.
+                        KeyboardNavigation.MoveNext((IInputElement)this.TemplatedParent);
+                    }
+                    else
+                    {
+                        KeyboardNavigation.MovePrevious((IInputElement)this.TemplatedParent);
+                    }
 
                     break;
 

Perspex.Controls/TextBox.cs

@@ -8,7 +8,11 @@ namespace Perspex.Controls
 {
     using System;
     using System.Reactive.Linq;
+    using Perspex.Controls.Presenters;
     using Perspex.Controls.Primitives;
+    using Perspex.Controls.Templates;
+    using Perspex.Input;
+    using Perspex.Interactivity;
 
     public class TextBox : TemplatedControl
     {
@@ -33,6 +37,13 @@ namespace Perspex.Controls
         public static readonly PerspexProperty<TextWrapping> TextWrappingProperty =
             TextBlock.TextWrappingProperty.AddOwner<TextBox>();
 
+        private TextPresenter presenter;
+
+        static TextBox()
+        {
+            FocusableProperty.OverrideDefaultValue(typeof(TextBox), true);
+        }
+
         public TextBox()
         {
             var canScrollHorizontally = this.GetObservable(AcceptsReturnProperty)
@@ -100,5 +111,17 @@ namespace Perspex.Controls
             var length = (text != null) ? text.Length : 0;
             return Math.Max(0, Math.Min(length, value));
         }
+
+        protected override void OnTemplateApplied()
+        {
+            this.presenter = this.GetTemplateChild<TextPresenter>("textPresenter");
+        }
+
+        protected override void OnGotFocus(RoutedEventArgs e)
+        {
+            // TODO: There needs to be a better way of setting focus to a templated child.
+            base.OnGotFocus(e);
+            FocusManager.Instance.Focus(this.presenter);
+        }
     }
 }

Perspex.Input/KeyboardNavigation.cs

@@ -0,0 +1,49 @@
+// -----------------------------------------------------------------------
+// <copyright file="FocusNavigationDirection.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Input
+{
+    using System.Linq;
+    using Perspex.VisualTree;
+
+    /// <summary>
+    /// TODO: This class is a temporary stop-gap just to add tab handling. Should be replaced 
+    /// with something better thought out and testable etc.
+    /// </summary>
+    public static class KeyboardNavigation
+    {
+        public static void MoveNext(IInputElement element)
+        {
+            var siblings = element.GetVisualSiblings().OfType<IInputElement>()
+                .Where(x => x.Focusable)
+                .SkipWhile(x => x != element)
+                .Skip(1);
+
+            var next = siblings.FirstOrDefault();
+
+            if (next != null)
+            {
+                FocusManager.Instance.Focus(next);
+            }
+        }
+
+        public static void MovePrevious(IInputElement element)
+        {
+            var siblings = element.GetVisualSiblings().OfType<IInputElement>()
+                .Where(x => x.Focusable)
+                .Reverse()
+                .SkipWhile(x => x != element)
+                .Skip(1);
+
+            var next = siblings.FirstOrDefault();
+
+            if (next != null)
+            {
+                FocusManager.Instance.Focus(next);
+            }
+        }
+    }
+}

Perspex.Input/Perspex.Input.csproj

@@ -72,6 +72,7 @@
     <Compile Include="IPointerDevice.cs" />
     <Compile Include="Key.cs" />
     <Compile Include="KeyboardDevice.cs" />
+    <Compile Include="KeyboardNavigation.cs" />
     <Compile Include="Platform\IPlatformSettings.cs" />
     <Compile Include="PointerPressEventArgs.cs" />
     <Compile Include="PointerWheelEventArgs.cs" />

Perspex.Themes.Default/TextBoxStyle.cs

@@ -55,6 +55,7 @@ namespace Perspex.Themes.Default
                     [~ScrollViewer.VerticalScrollBarVisibilityProperty] = control[~ScrollViewer.VerticalScrollBarVisibilityProperty],
                     Content = new TextPresenter
                     {
+                        Id = "textPresenter",
                         [~TextPresenter.AcceptsReturnProperty] = control[~TextBox.AcceptsReturnProperty],
                         [~TextPresenter.AcceptsTabProperty] = control[~TextBox.AcceptsTabProperty],
                         [~TextPresenter.CaretIndexProperty] = control[~TextBox.CaretIndexProperty],