PropertyGrid: no longer support the ExpandableObjectConverter syntax for defining a complex property. I have added a new attribute called ExpandableObjectAttribute.

The syntax is as follows: 

public class Person
    {
        [Description("First Name")]
        public string FirstName { get; set; }
        [Description("Last Name")]
        public string LastName { get; set; }

        [ExpandableObject]
        public Person Spouse { get; set; }
    }

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/PropertyGrid/Implementation/Attributes/ExpandableObjectAttribute.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace Microsoft.Windows.Controls.PropertyGrid.Attributes
+{
+    public class ExpandableObjectAttribute : Attribute
+    {
+        public ExpandableObjectAttribute()
+        {
+
+        }
+    }
+}

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/PropertyGrid/Implementation/PropertyItem.cs

@@ -8,6 +8,7 @@ using System.Windows.Data;
 using System.Windows.Input;
 using System.Windows.Markup.Primitives;
 using Microsoft.Windows.Controls.PropertyGrid.Commands;
+using Microsoft.Windows.Controls.PropertyGrid.Attributes;
 
 namespace Microsoft.Windows.Controls.PropertyGrid
 {
@@ -334,8 +335,8 @@ namespace Microsoft.Windows.Controls.PropertyGrid
 
             if (!IsReadOnly)
             {
-                TypeConverter converter = PropertyDescriptor.Converter;
-                if (converter is ExpandableObjectConverter && PropertyDescriptor.GetValue(Instance) != null)
+                var attribute = PropertyGridUtilities.GetAttribute<ExpandableObjectAttribute>(PropertyDescriptor);
+                if (attribute != null && PropertyDescriptor.GetValue(Instance) != null)
                 {
                     HasChildProperties = true;
                 }
@@ -384,12 +385,7 @@ namespace Microsoft.Windows.Controls.PropertyGrid
 
         private void GetChildProperties()
         {
-            TypeConverter converter = PropertyDescriptor.Converter;
-
-            PropertyDescriptorCollection descriptors = null;
-
-            if (converter is ExpandableObjectConverter)
-                descriptors = PropertyDescriptor.GetChildProperties();
+            PropertyDescriptorCollection descriptors = PropertyDescriptor.GetChildProperties();
 
             var propertyItems = new List<PropertyItem>();
 

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/WPFToolkit.Extended.csproj

@@ -237,6 +237,7 @@
       <DesignTimeSharedInput>True</DesignTimeSharedInput>
     </Compile>
     <Compile Include="BusyIndicator\Implementation\VisualStates.BusyIndicator.cs" />
+    <Compile Include="PropertyGrid\Implementation\Attributes\ExpandableObjectAttribute.cs" />
     <Compile Include="PropertyGrid\Implementation\Attributes\IItemsSource.cs" />
     <Compile Include="PropertyGrid\Implementation\Attributes\ItemsSourceAttribute.cs" />
     <Compile Include="PropertyGrid\Implementation\Commands\PropertyGridCommands.cs" />