dotnet/wpf · error · ArgumentException

SR.UnsupportedProperty

Error message

SR.UnsupportedProperty

What it means

ItemContainerPattern.FindItemByProperty validates the supplied AutomationProperty via Schema.GetPropertyInfo; if the property is not a recognized UI Automation property, ArgumentException(SR.UnsupportedProperty) is thrown. The pattern can only search against properties registered in the UIA schema.

Solutions

1. Use only properties from AutomationElement or its pattern identifier classes (e.g. AutomationElementIdentifiers)
2. Verify the property is a recognized UIA property before calling FindItemByProperty
3. Pass AutomationElement.NotSupported as the value to search on all items if filtering is unnecessary

Example fix

// before
var prop = AutomationProperty.LookupById(99999); // unknown/custom
pattern.FindItemByProperty(null, prop, "x"); // ArgumentException
// after
pattern.FindItemByProperty(null, AutomationElement.NameProperty, "x");

static readonly HashSet<AutomationProperty> Known = new(){ AutomationElement.NameProperty, AutomationElement.AutomationIdProperty, AutomationElement.ControlTypeProperty /* ... */ };
if (!Known.Contains(prop)) throw new InvalidOperationException("Unknown property for FindItemByProperty");

bool IsKnownUiaProperty(AutomationProperty p) => p == AutomationElement.NameProperty || p == AutomationElement.AutomationIdProperty || p == AutomationElement.ControlTypeProperty;

try { pattern.FindItemByProperty(null, prop, value); } catch (ArgumentException ex) { /* log unsupported property, fall back to enumeration */ }

When it happens

Trigger: Passing a custom AutomationProperty, a property from another provider framework, or a null/unknown identifier to FindItemByProperty(property, value).

Common situations: Hand-rolled AutomationProperty instances or properties from a newer UIA version not known to the client; mixing properties from different element registries; typos when selecting a property identifier.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• SR.Format(SR.PropertyConditionIncorrectType…
• SR.UnsupportedProperty
• E_INVALIDARG
• name
• SR.BeginEndTextContainerMismatch

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/752233f7824f87fa. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClient/System/Windows/Automation/ItemContainerPattern.cs:129

           return wrappedElement;
        }

        #endregion Public Methods

       //------------------------------------------------------
       //
       //  Private Methods
       //
       //------------------------------------------------------

       #region Private Methods

        private object PropertyValueValidateAndMap(AutomationProperty property, object value)
        {
            AutomationPropertyInfo info;
            if (!Schema.GetPropertyInfo(property, out info))
            {
                throw new ArgumentException(SR.UnsupportedProperty);
            }

            // Check type is appropriate: NotSupported is allowed against any property,
            // null is allowed for any reference type (ie not for value types), otherwise
            // type must be assignable from expected type.
            Type expectedType = info.Type;
            if (value != AutomationElement.NotSupported &&
                ((value == null && expectedType.IsValueType)
                || (value != null && !expectedType.IsAssignableFrom(value.GetType()))))
            {
                throw new ArgumentException(SR.Format(SR.PropertyConditionIncorrectType, property.ProgrammaticName, expectedType.Name));
            }

            // Some types are handled differently in managed vs unmanaged - handle those here...
            if (value is AutomationElement)
            {
                // If this is a comparison against a Raw/LogicalElement,
                // save the runtime ID instead of the element so that we

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