dotnet/wpf · error · ArgumentException

SR.PropertyNotSupported

Error message

SR.PropertyNotSupported

What it means

ItemsControlAutomationPeer.FindItemByProperty/GetChildrenCore path validates the propertyId passed by the UIA client: if a non-zero property id is given and it is not one of the properties supported by this control for find-item operations, it throws ArgumentException(SR.PropertyNotSupported). This tells the client the requested property cannot be used as a filter.

Solutions

  1. Pass only properties supported for find-item (typically AutomationIdProperty or NameProperty) or null/0 to match any property.
  2. Use FindFirst/TreeWalker with manual property comparison instead of FindItemByProperty for unsupported properties.
  3. Catch ArgumentException and fall back to enumerating children and comparing the property yourself.

Example fix

// before
container.FindItemByProperty(null, SelectionItemPattern.IsSelectedProperty, true); // unsupported
// after
var item = container.FindItemByProperty(null, AutomationElement.AutomationIdProperty, targetId);
Defensive patterns

Strategy: validation

Validate before calling

if (propertyId != 0 && propertyId != AutomationElement.AutomationIdProperty.Id && propertyId != AutomationElement.NameProperty.Id) throwSkipFind();

Type guard

bool IsSupportedFindProperty(int id) => id == 0 || id == AutomationElement.AutomationIdProperty.Id || id == AutomationElement.NameProperty.Id;

Try / catch

try { container.FindItemByProperty(start, prop, value); } catch (ArgumentException) { /* enumerate children manually */ }

Prevention

When it happens

Trigger: Calling UI FindItemByProperty (IItemContainerProvider.FindItemByProperty) with a propertyId that the ItemsControl does not support for filtering (only AutomationIdProperty, NameProperty, etc. are typically supported).

Common situations: UIA clients using IItemContainerProvider to search items by a property like IsSelectedProperty or a custom property; generic test frameworks passing arbitrary AutomationProperty ids.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/b5a6e85f29dc5eb0. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/ItemsControlAutomationPeer.cs:235

            ItemsControl owner = this.Owner as ItemsControl;
            ItemCollection items = owner.Items;
            if(items != null)
            {
                if(GetPeerFromWeakRefStorage(itemPeer.Item) == null)
                    WeakRefElementProxyStorage[itemPeer.Item] = wr;
            }
        }

        ///
        IRawElementProviderSimple IItemContainerProvider.FindItemByProperty(IRawElementProviderSimple startAfter, int propertyId, object value)
        {
            ResetChildrenCache();
            // Checks if propertyId is valid else throws ArgumentException to notify it as invalid argument is being passed
            if (propertyId != 0)
            {
                if (!IsPropertySupportedByControlForFindItem(propertyId))
                {
                    throw new ArgumentException(SR.PropertyNotSupported);
                }
            }

            ItemsControl owner = (ItemsControl)Owner;

            ItemCollection items = null;
            if(owner != null)
                items = owner.Items;

            if (items != null && items.Count > 0)
            {
                ItemAutomationPeer startAfterItem = null;
                if (startAfter != null)
                {
                    // get the peer corresponding to this provider
                    startAfterItem = PeerFromProvider(startAfter) as ItemAutomationPeer;
                    if(startAfterItem == null)
                        return null;

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