Handle non Control-derived classes in DevTools.

Previously DevTools expected all controls to be derived from `Control`
which isn't necessarily always the case.

src/Avalonia.Diagnostics/ViewModels/ControlDetailsViewModel.cs

@@ -3,19 +3,19 @@
 
 using System.Collections.Generic;
 using System.Linq;
-using Avalonia.Controls;
+using Avalonia.VisualTree;
 using ReactiveUI;
 
 namespace Avalonia.Diagnostics.ViewModels
 {
     internal class ControlDetailsViewModel : ReactiveObject
     {
-        public ControlDetailsViewModel(Control control)
+        public ControlDetailsViewModel(IVisual control)
         {
-            if (control != null)
+            if (control is AvaloniaObject avaloniaObject)
             {
-                Properties = AvaloniaPropertyRegistry.Instance.GetRegistered(control)
-                    .Select(x => new PropertyDetails(control, x))
+                Properties = AvaloniaPropertyRegistry.Instance.GetRegistered(avaloniaObject)
+                    .Select(x => new PropertyDetails(avaloniaObject, x))
                     .OrderBy(x => x.IsAttached)
                     .ThenBy(x => x.Name);
             }

src/Avalonia.Diagnostics/ViewModels/TreeNode.cs

@@ -7,6 +7,7 @@ using System.Reactive;
 using System.Reactive.Linq;
 using Avalonia.Controls;
 using Avalonia.Styling;
+using Avalonia.VisualTree;
 using ReactiveUI;
 
 namespace Avalonia.Diagnostics.ViewModels
@@ -16,32 +17,35 @@ namespace Avalonia.Diagnostics.ViewModels
         private string _classes;
         private bool _isExpanded;
 
-        public TreeNode(Control control, TreeNode parent)
+        public TreeNode(IVisual control, TreeNode parent)
         {
-            Control = control;
             Parent = parent;
             Type = control.GetType().Name;
+            Control = control;
 
-            var classesChanged = Observable.FromEventPattern<
-                    NotifyCollectionChangedEventHandler, 
-                    NotifyCollectionChangedEventArgs>(
-                x => control.Classes.CollectionChanged += x,
-                x => control.Classes.CollectionChanged -= x)
-                .TakeUntil(((IStyleable)control).StyleDetach);
+            if (control is IStyleable styleable)
+            {
+                var classesChanged = Observable.FromEventPattern<
+                        NotifyCollectionChangedEventHandler,
+                        NotifyCollectionChangedEventArgs>(
+                    x => styleable.Classes.CollectionChanged += x,
+                    x => styleable.Classes.CollectionChanged -= x)
+                    .TakeUntil(((IStyleable)styleable).StyleDetach);
 
-            classesChanged.Select(_ => Unit.Default)
-                .StartWith(Unit.Default)
-                .Subscribe(_ =>
-                {
-                    if (control.Classes.Count > 0)
-                    {
-                        Classes = "(" + string.Join(" ", control.Classes) + ")";
-                    }
-                    else
+                classesChanged.Select(_ => Unit.Default)
+                    .StartWith(Unit.Default)
+                    .Subscribe(_ =>
                     {
-                        Classes = string.Empty;
-                    }
-                });
+                        if (styleable.Classes.Count > 0)
+                        {
+                            Classes = "(" + string.Join(" ", styleable.Classes) + ")";
+                        }
+                        else
+                        {
+                            Classes = string.Empty;
+                        }
+                    });
+            }
         }
 
         public IReadOnlyReactiveList<TreeNode> Children
@@ -56,7 +60,7 @@ namespace Avalonia.Diagnostics.ViewModels
             private set { this.RaiseAndSetIfChanged(ref _classes, value); }
         }
 
-        public Control Control
+        public IVisual Control
         {
             get;
         }

src/Avalonia.Diagnostics/ViewModels/VisualTreeNode.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using Avalonia.Controls;
+using Avalonia.Styling;
 using Avalonia.VisualTree;
 using ReactiveUI;
 
@@ -10,7 +11,7 @@ namespace Avalonia.Diagnostics.ViewModels
     internal class VisualTreeNode : TreeNode
     {
         public VisualTreeNode(IVisual visual, TreeNode parent)
-            : base((Control)visual, parent)
+            : base(visual, parent)
         {
             var host = visual as IVisualTreeHost;
 
@@ -23,9 +24,9 @@ namespace Avalonia.Diagnostics.ViewModels
                 Children = new ReactiveList<VisualTreeNode>(new[] { new VisualTreeNode(host.Root, this) });
             }
 
-            if (Control != null)
+            if ((Control is IStyleable styleable))
             {
-                IsInTemplate = Control.TemplatedParent != null;
+                IsInTemplate = styleable.TemplatedParent != null;
             }
         }