fix: Support custom markup extensions in XamlReader.Load #22073

Copilot · 2025-12-10T02:13:28Z

Summary

Fixed an issue where XamlReader.Load would throw NotSupportedException when encountering custom markup extensions (e.g., {utu:Responsive Narrow=1, Wide=2}).

Changes

Modified IsMarkupExtension to detect any type inheriting from MarkupExtension using new IsCustomMarkupExtension helper
Added ProcessCustomMarkupExtension to handle custom markup extension evaluation with proper error handling and collection property support
Added unit tests to verify custom markup extensions work correctly

Latest Fix

Fixed test failure in When_MarkupExtension_ServiceProvider_InlineLiteral by adding support for collection properties (like Panel.Children). The method now:

Checks if the target property is an initialized collection using TypeResolver.IsInitializedCollection
Gets the collection instance via the property getter
Adds the markup extension result to the collection using the Add method
Falls back to normal property setter for non-collection properties

Closes https://github.com/unoplatform/uno/issues/XXXXX

Original prompt

This section details on the original issue you should resolve

<issue_title>XamlReader.Load exception - unable to parse markup extension</issue_title>
<issue_description>### Current behavior 🐛

Attempting to call XamlReader.Load on XAML that contains uses a custom markup extension fail to parse

var xaml =
    """
    <Grid Grid.RowSpan="{utu:Responsive Narrow=1, Wide=2}" xmlns:utu="using:Uno.Toolkit.UI" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" />
    """;

var element = XamlReader.Load(xaml) as UIElement;

Sample App
ParsingSample.zip

Expected behavior 🎯

No parsing errors - markup extension should be correctly parsed and loaded

How to reproduce it (as minimally and precisely as possible) 🔬

No response

Workaround 🛠️

No response

Renderer 🎨

Skia
Native

Affected platforms 📱💻🖥️

No response

Uno.Sdk version (and other relevant versions) 📦

Uno.Sdk 6.4.40

IDE version 🧑‍💻

Visual Studio 2026 18.0.2

Anything else we need to know? 💬

Call Stack:

 	 	[Uno.Xaml.XamlParseException user-unhandled]	
 	Uno.UI.dll!Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.Build(object component, bool createInstanceFromXClass)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.Markup.XamlReader.Load(string xaml)	Unknown
>	ParsingSampleApp.dll!ParsingSampleApp.MainPage.RunMarkupClicked(object sender, Microsoft.UI.Xaml.RoutedEventArgs e) Line 33	C#
 	ParsingSampleApp.dll!ParsingSampleApp.MainPage.__MainPage_3d1508bf9a2ba168f5d35e6e084167f9.__PagΞ0_ScrVieΞ0_GriΞ0_StaPanΞ2_But_Cli_Click_Handler.Invoke(object sender, Microsoft.UI.Xaml.RoutedEventArgs e) Line 226	C#
 	Uno.UI.dll!Microsoft.UI.Xaml.Controls.Primitives.ButtonBase.OnClick()	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.Controls.Button.OnClick()	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.Controls.Primitives.ButtonBase.PerformPointerUpAction()	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.Controls.Primitives.ButtonBase.OnPointerReleased(Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.Controls.Control..cctor.AnonymousMethod__389_10(object sender, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.InvokeHandler(object handler, Microsoft.UI.Xaml.RoutedEventArgs args)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.InvokeHandlers(System.Collections.Generic.IList<Microsoft.UI.Xaml.UIElement.RoutedEventHandlerInfo> handlers, Microsoft.UI.Xaml.RoutedEventArgs args, ref bool isHandled)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.RaiseEvent(Microsoft.UI.Xaml.RoutedEvent routedEvent, Microsoft.UI.Xaml.RoutedEventArgs args, Microsoft.UI.Xaml.UIElement.BubblingContext ctx)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.RaisePointerEvent.__InnerRaiseEvent|662_0(Microsoft.UI.Xaml.RoutedEvent evt, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args, Microsoft.UI.Xaml.UIElement.BubblingContext ctx, ref (Microsoft.UI.Xaml.UIElement sender, Microsoft.UI.Xaml.RoutedEvent event, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args) pendingRaisedEvent)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.RaisePointerEvent(Microsoft.UI.Xaml.RoutedEvent evt, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args, Microsoft.UI.Xaml.UIElement.BubblingContext ctx)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.SetPressed(Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args, bool isPressed, Microsoft.UI.Xaml.UIElement.BubblingContext ctx)	Unknown
 	Uno.UI.dll!Microsoft.UI.Xaml.UIElement.OnPointerUp(Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args, Microsoft.UI.Xaml.UIElement.BubblingContext ctx)	Unknown
 	Uno.UI.dll!Uno.UI.Xaml.Core.InputManager.PointerManager..cctor.AnonymousMethod__88_5(Microsoft.UI.Xaml.UIElement elt, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs args, Microsoft.UI.Xaml.UIElement.BubblingContext ctx)	Unknown
 	Uno.UI.dll!Uno.UI.Xaml.Core.InputManager.PointerManager.RaiseUsingCaptures(Uno.UI.Xaml.Core.InputManager.PointerManager.PointerEvent evt, Microsoft.UI.Xaml.UIElement originalSource, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs routedArgs, bool setCursor)	Unknown
 	Uno.UI.dll!Uno.UI.Xaml.Core.InputManager.PointerManager.OnPointerReleased(Windows.UI.Core.PointerEventArgs args, bool isInjected)	Unknown
 	Uno.UI.dll!Uno.UI.Xaml.Core.InputManager.PointerManager.Init.AnonymousMethod__17_4(object c, Windows.UI.Core.PointerEventArgs e)	Unknown
 	Uno.UI.Runtime.Skia.Win32.dll!Uno.UI.Runtime.Skia.Win32.Win32WindowWrapper.OnPointer(uint msg, Windows.Win32.Foundation.WPARAM wParam, Windows.Win32.Foundation.HWND hwnd)	Unknown
 	Uno.UI.Runtime.Skia.Win32.dll!Uno.UI.Runtime.Skia.Win32.Win32WindowWrapper.WndProcInner(Windows.Win32.Foundation.HWND hwnd, uint msg, Windows.Win32.Foundation.WPARAM wParam, Windo...

</details>



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- Fixes unoplatform/uno#22011

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Co-authored-by: nickrandolph <[email protected]>

CLAassistant · 2025-12-10T02:35:56Z

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unodevops · 2025-12-10T02:38:52Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22073/docs/index.html

Co-authored-by: nickrandolph <[email protected]>

unodevops · 2025-12-10T03:12:09Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22073/docs/index.html

unodevops · 2025-12-10T04:10:43Z

⚠️⚠️ The build 187175 has failed on Uno.UI - CI.

nickrandolph · 2025-12-19T03:09:52Z

@copilot fix test error:

Error message

View

Copy
System.InvalidOperationException: Exception thrown while invoking Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Markup.Given_XamlReader.When_MarkupExtension_ServiceProvider_InlineLiteral() with arguments { }.
---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
---> Uno.Xaml.XamlParseException: Failed to parse member (Failed to process custom markup extension 'DebugMarkupExtension'. [Line: 3 Position: 5]) [Line: 3 Position: 5]
---> Uno.Xaml.XamlParseException: Failed to process custom markup extension 'DebugMarkupExtension'. [Line: 3 Position: 5]
---> System.InvalidOperationException: Unable to find setter for property [Microsoft.UI.Xaml.Controls.UIElementCollection Children]
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.GetPropertySetter(PropertyInfo propertyInfo) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 947
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.ProcessCustomMarkupExtension(Object instance, Object rootInstance, XamlMemberDefinition member, PropertyInfo propertyInfo) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 1052
--- End of inner exception stack trace ---
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.ProcessCustomMarkupExtension(Object instance, Object rootInstance, XamlMemberDefinition member, PropertyInfo propertyInfo) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 1063
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.ProcessMemberMarkupExtension(Object instance, Object rootInstance, XamlMemberDefinition member, PropertyInfo propertyInfo) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 962
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.ProcessNamedMember(XamlObjectDefinition control, Object instance, XamlMemberDefinition member, Object rootInstance, TemplateMaterializationSettings settings) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 526
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.LoadObject(XamlObjectDefinition control, Object rootInstance, Object component, TemplateMaterializationSettings settings, MemberInitializationContext memberContext, Boolean createInstanceFromXClass) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 363
--- End of inner exception stack trace ---
at Microsoft.UI.Xaml.Markup.Reader.XamlObjectBuilder.Build(Object component, Boolean createInstanceFromXClass) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\Reader\XamlObjectBuilder.cs:line 124
at Microsoft.UI.Xaml.Markup.XamlReader.Load(String xaml) in D:\a\1\s\src\Uno.UI\UI\Xaml\Markup\XamlReader.cs:line 15
at Uno.UI.Helpers.XamlHelper.LoadXaml[T](String xaml, Dictionary`2 xmlnses) in D:\a\1\s\src\Uno.UI\Helpers\XamlHelper.cs:line 74
at Uno.UI.Helpers.XamlHelper.LoadXaml[T](String xaml, Boolean autoInjectXmlns) in D:\a\1\s\src\Uno.UI\Helpers\XamlHelper.cs:line 58
at Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Markup.Given_XamlReader.When_MarkupExtension_ServiceProvider_InlineLiteral() in D:\a\1\s\src\Uno.UI.RuntimeTests\Tests\Windows_UI_Xaml_Markup\Given_XamlReader.cs:line 593
at InvokeStub_Given_XamlReader.When_MarkupExtension_ServiceProvider_InlineLiteral(Object, Object, IntPtr*)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
--- End of inner exception stack trace ---
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Uno.UI.Samples.Tests.UnitTestsControl.InvokeMethod(MethodInfo method, Object instance, Object[] methodArguments) in D:\a\1\s\src\SamplesApp\SamplesApp.UnitTests.Shared\Controls\UnitTest\UnitTestsControl.cs:line 1149
--- End of inner exception stack trace ---
at Uno.UI.Samples.Tests.UnitTestsControl.InvokeMethod(MethodInfo method, Object instance, Object[] m

Co-authored-by: nickrandolph <[email protected]>

Copilot · 2025-12-19T03:13:55Z

@copilot fix test error:

Error message
...

Fixed in commit e775744. The issue was that collection properties like Panel.Children don't have setters. Added logic to check TypeResolver.IsInitializedCollection and use the Add method to add the markup extension result to the collection instead of trying to set the property value.

unodevops · 2025-12-19T03:33:54Z

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22073/wasm-skia-net9/index.html

unodevops · 2025-12-19T03:35:59Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22073/docs/index.html

Initial plan

e0bd064

Copilot AI assigned Copilot and nickrandolph Dec 10, 2025

Copilot started work on behalf of nickrandolph December 10, 2025 02:13 View session

fix: Support custom markup extensions in XamlReader.Load

fc73665

Co-authored-by: nickrandolph <[email protected]>

Copilot AI and others added 3 commits December 10, 2025 02:42

chore: Fix code formatting

74ac916

Co-authored-by: nickrandolph <[email protected]>

fix: Avoid redundant Extension suffix lookup

b1f2203

Co-authored-by: nickrandolph <[email protected]>

fix: Add better error handling for custom markup extensions

ff0cd21

Co-authored-by: nickrandolph <[email protected]>

Copilot AI changed the title ~~[WIP] Fix XamlReader.Load exception for custom markup extension~~ fix: Support custom markup extensions in XamlReader.Load Dec 10, 2025

Copilot AI requested a review from nickrandolph December 10, 2025 02:50

Copilot finished work on behalf of nickrandolph December 10, 2025 02:50

nickrandolph mentioned this pull request Dec 19, 2025

fix: XamlReader.Load fails to parse custom markup extensions #22150

Closed

12 tasks

Copilot started work on behalf of nickrandolph December 19, 2025 03:10 View session

fix: Handle collection properties in custom markup extensions

e775744

Co-authored-by: nickrandolph <[email protected]>

Copilot finished work on behalf of nickrandolph December 19, 2025 03:15

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Summary

Changes

Latest Fix

Expected behavior 🎯

How to reproduce it (as minimally and precisely as possible) 🔬

Workaround 🛠️

Renderer 🎨

Affected platforms 📱💻🖥️

Uno.Sdk version (and other relevant versions) 📦

IDE version 🧑‍💻

Anything else we need to know? 💬

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