unoplatform/uno · error · NotSupportedException

Field modifier {accessibility} is not supported

Error message

Field modifier {accessibility} is not supported

What it means

Thrown by the accessibility-to-string conversion method when a field's Accessibility value does not match Private, Internal, or Public. The switch has a default case that throws NotSupportedException for any other accessibility level (Protected, ProtectedOrInternal, ProtectedAndInternal, etc.).

Source

Thrown at src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.Reflection.cs:253

			return Accessibility.Private;
		}

		private string FormatAccessibility(Accessibility accessibility)
		{
			switch (accessibility)
			{
				case Accessibility.Private:
					return "private";

				case Accessibility.Internal:
					return "internal";

				case Accessibility.Public:
					return "public";

				default:
					throw new NotSupportedException($"Field modifier {accessibility} is not supported");
			}
		}

		private INamedTypeSymbol GetPropertyTypeByOwnerSymbol(INamedTypeSymbol ownerType, string propertyName, int lineNumber, int linePosition, [CallerMemberName] string caller = "")
		{
			var definition = _metadataHelper.FindPropertyTypeByOwnerSymbol(ownerType, propertyName);

			if (definition == null)
			{
				throw new Exception($"The property {ownerType}.{propertyName} is unknown. Line number: {lineNumber}, Line position: {linePosition}, Caller: {caller}, File: {_fileDefinition.FilePath}");
			}

			return definition;
		}

		private ISymbol? FindProperty(XamlMember xamlMember)
		{
			var type = FindType(xamlMember.DeclaringType);

View on GitHub (pinned to 0418340488)

Solutions

1. Change the field's accessibility to public, internal, or private.
2. If the field is inherited and cannot be changed, create a public/internal wrapper property and bind to that instead.
3. Move the field declaration to a context where it can be public/internal.

Example fix

// before
protected string _myValue;
<!-- XAML binds to _myValue -->
// after
public string MyValue { get => _myValue; set => _myValue = value; }

// Check field accessibility before binding in XAML:
// var fields = typeof(MyPage).GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
// foreach (var f in fields.Where(f => f.IsFamily || f.IsFamilyOrAssembly))
//     Console.WriteLine($"Field {f.Name} is {f.Attributes} — change to public/internal/private for XAML");

When it happens

Trigger: A field used in XAML code generation (e.g. an x:Bind source field or a named element backing field) has a protected or protected-internal accessibility modifier.

Common situations: A field declared as 'protected' in a base class or partial class is picked up by the XAML generator; code that was refactored from public to protected without updating XAML bindings; an inherited protected field is bound via x:Bind.

Related errors

• The property {ownerType}.{propertyName} is unknown. Line num
• The {0} string passed in the colorString argument is not a r
• Member '{0}' could not be resolved to a static member
• Attempt to set value from read-only property {0}
• Current operation is valid only when the underlying type on

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/b749a59b8ac7e3e9. Report an issue: GitHub.