Use an anchor for dynamic resources.

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs

@@ -2,14 +2,19 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using System.ComponentModel;
 using Avalonia.Controls;
 using Avalonia.Data;
+using Portable.Xaml;
+using Portable.Xaml.ComponentModel;
 using Portable.Xaml.Markup;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class DynamicResourceExtension : MarkupExtension, IBinding
     {
+        private IControl _anchor;
+
         public DynamicResourceExtension()
         {
         }
@@ -21,7 +26,18 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public string ResourceKey { get; set; }
 
-        public override object ProvideValue(IServiceProvider serviceProvider) => this;
+        public override object ProvideValue(IServiceProvider serviceProvider)
+        {
+            var context = (ITypeDescriptorContext)serviceProvider;
+            var provideTarget = context.GetService<IProvideValueTarget>();
+
+            if (!(provideTarget.TargetObject is IControl))
+            {
+                _anchor = GetAnchor<IControl>(context);
+            }
+
+            return this;
+        }
 
         InstancedBinding IBinding.Initiate(
             IAvaloniaObject target,
@@ -29,7 +45,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             object anchor,
             bool enableDataValidation)
         {
-            if (target is IControl control)
+            var control = target as IControl ?? _anchor as IControl;
+
+            if (control != null)
             {
                 var resource = control.FindResource(ResourceKey);
                 return new InstancedBinding(resource);
@@ -37,5 +55,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             return null;
         }
+
+        private T GetAnchor<T>(ITypeDescriptorContext context) where T : class
+        {
+            var schemaContext = context.GetService<IXamlSchemaContextProvider>()?.SchemaContext;
+            var ambientProvider = context.GetService<IAmbientProvider>();
+            var xamlType = schemaContext.GetXamlType(typeof(T));
+            return ambientProvider.GetFirstAmbientValue(xamlType) as T;
+        }
     }
 }

tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/DynamicResourceTests.cs

@@ -277,7 +277,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
         }
 
         [Fact]
-        public void DynamicResource_Can_Be_Found_Across_Xaml_Files()
+        public void DynamicResource_Can_Be_Found_Across_Xaml_Style_Files()
         {
             var style1Xaml = @"
 <Style xmlns='https://github.com/avaloniaui'