AvaloniaUI/Avalonia · error · InvalidOperationException

Cannot find property {type}.{attached.PropertyName}.

Error message

Cannot find property {type}.{attached.PropertyName}.

What it means

In string/reflection bindings, ExpressionNodeFactory.AttachedPropertyNode resolves an attached property like `(Grid.Row)` by calling AvaloniaPropertyRegistry.Instance.FindRegistered(ownerType, propertyName). If no AvaloniaProperty with that name is registered on the resolved owner type, it throws InvalidOperationException. This is the reflection-binding code path; compiled bindings resolve attached properties through the visitor instead.

Source

Thrown at src/Avalonia.Base/Data/Core/Parsers/ExpressionNodeFactory.cs:117

                    new VisualAncestorElementNode(source.AncestorType, source.AncestorLevel - 1),
                _ => throw new NotSupportedException("Unsupported RelativeSource mode.")
            };
        }

        public static ExpressionNode CreateDataContext(AvaloniaProperty? targetProperty)
        {
            return targetProperty == StyledElement.DataContextProperty ? 
                new ParentDataContextNode() :
                new DataContextNode();
        }

        private static AvaloniaPropertyAccessorNode AttachedPropertyNode(
            Func<string?, string, Type?>? typeResolver,
            BindingExpressionGrammar.AttachedPropertyNameNode attached)
        {
            var type = LookupType(typeResolver, attached.Namespace, attached.TypeName);
            var property = AvaloniaPropertyRegistry.Instance.FindRegistered(type, attached.PropertyName) ??
                throw new InvalidOperationException($"Cannot find property {type}.{attached.PropertyName}.");
            return new AvaloniaPropertyAccessorNode(property);
        }

        private static LogicalAncestorElementNode LogicalAncestorNode(
            Func<string?, string, Type?>? typeResolver,
            BindingExpressionGrammar.AncestorNode ancestor)
        {
            Type? type = null;

            if (!string.IsNullOrEmpty(ancestor.TypeName))
            {
                type = LookupType(typeResolver, ancestor.Namespace, ancestor.TypeName);
            }

            return new LogicalAncestorElementNode(type, ancestor.Level);
        }

        private static Type LookupType(

View on GitHub (pinned to 11c5427268)

Solutions

1. Verify the owner type and property name spelling against AvaloniaPropertyRegistry registrations.
2. Ensure the declaring assembly is referenced and the AvaloniaProperty is registered (static field initializer preserved).
3. For trimming, root the registration with DynamicDependency / preserve initializers.

Example fix

<!-- before -->
<Binding Path="(Gird.Row)"/>
<!-- after -->
<Binding Path="(Grid.Row)"/>

// Before using an attached property name, confirm it is registered:
static bool IsAttachedPropertyRegistered(Type ownerType, string name) =>
    AvaloniaPropertyRegistry.Instance.FindRegistered(ownerType, name) is not null;

When it happens

Trigger: <Binding Path="(WrongType.NonExistentProperty)"/>, a typo in the attached property name, or a property whose owning type was trimmed away so it is no longer registered.

Common situations: Misspelled owner type or property name; wrong xmlns prefix; attached property declared in an assembly that is not referenced; IL trimming/AOT removing the static field initializer that registers the AvaloniaProperty.

Related errors

• Unable to resolve type '{@namespace}:{name}'.
• Invalid attached property name.
• Attached Property name expected after '.'.
• Expected ')'.
• Unable to resolve unnamed type from namespace '{@namespace}'

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/bf17ee49822781ad. Report an issue: GitHub.