Fixed #2228

src/Markup/Avalonia.Markup.Xaml/AvaloniaTypeConverters.cs

@@ -44,6 +44,12 @@ namespace Avalonia.Markup.Xaml
             { typeof(FontFamily), typeof(FontFamilyTypeConverter) }
         };
 
+        internal static Type GetBuiltinTypeConverter(Type type)
+        {
+            _converters.TryGetValue(type, out var result);
+            return result;
+        }
+
         /// <summary>
         /// Tries to lookup a <see cref="TypeConverter"/> for a type.
         /// </summary>

src/Markup/Avalonia.Markup.Xaml/PortableXaml/AvaloniaTypeAttributeProvider.cs

@@ -42,7 +42,10 @@ namespace Avalonia.Markup.Xaml.PortableXaml
             }
             else if (attributeType == typeof(TypeConverterAttribute))
             {
-                result = ti.GetCustomAttribute(attributeType, inherit);
+                var builtin = AvaloniaTypeConverters.GetBuiltinTypeConverter(_type);
+                if (builtin != null)
+                    result = new TypeConverterAttribute(builtin);
+                result = result ?? ti.GetCustomAttribute(attributeType, inherit);
 
                 if (result == null)
                 {
@@ -111,4 +114,4 @@ namespace Avalonia.Markup.Xaml.PortableXaml
             return null;
         }
     }
-}
+}

tests/Avalonia.Markup.Xaml.UnitTests/Converters/ConverterTests.cs

@@ -0,0 +1,23 @@
+using System;
+using Xunit;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Converters
+{
+    public class ConverterTests
+    {
+        [Fact]
+        public void Bug_2228_Relative_Uris_Should_Be_Correctly_Parsed()
+        {
+            var testClass = typeof(TestClassWithUri);
+            var parsed = AvaloniaXamlLoader.Parse<TestClassWithUri>(
+                $"<{testClass.Name} xmlns='clr-namespace:{testClass.Namespace}' Uri='/test'/>", testClass.Assembly);
+
+            Assert.False(parsed.Uri.IsAbsoluteUri);
+        }
+    }
+    
+    public class TestClassWithUri
+    {
+        public Uri Uri { get; set; }
+    }
+}