dotnet/wpf · error · ArgumentException

E_INVALIDARG

E_INVALIDARG

Error message

SR.InvalidParameter

What it means

The MSAA/IAccessible server returned E_INVALIDARG, and the provider rethrows it as ArgumentException(SR.InvalidParameter). Per the MSAA contract this occurs when the caller identifies a child object using an identifier (childId/varChild) the server does not recognize, or attempts to identify a child within an object that has no children. The library maps it to ArgumentException because it almost always indicates a bad child id being passed down to the native provider.

Solutions

1. Re-enumerate children fresh (FindAll(TreeScope.Children)) instead of reusing cached child elements/ids after the UI changed.
2. Catch ElementNotAvailableException/ArgumentException around child navigation and treat as 'child no longer exists' rather than a programming bug.
3. If you own the provider, verify the childId passed to accChild/get_accChild calls matches what the server advertised (self id 0 vs 1-based child ids).
4. Update .NET/WPF — some OLEACC proxy quirks with child id handling were fixed in later framework servicing releases.

Example fix

// before
var child = children[i];
var name = child.Current.Name; // stale child id -> ArgumentException(SR.InvalidParameter)
// after
var fresh = parent.FindAll(TreeScope.Children, Condition.TrueCondition);
foreach (AutomationElement child in fresh)
{
    try { Console.WriteLine(child.Current.Name); }
    catch (ArgumentException) { /* server rejected child id; skip */ }
}

// Validate a child reference before use:
bool ChildExists(AutomationElement parent, AutomationElement child)
{
    var kids = parent.FindAll(TreeScope.Children, Condition.TrueCondition);
    foreach (AutomationElement k in kids) if (Automation.Compare(k, child)) return true;
    return false;
}

try
{
    var name = childElement.Current.Name;
}
catch (ArgumentException)
{
    // server rejected the child id; child set changed — re-enumerate
    childElement = parent.FindFirst(TreeScope.Children, condition);
}

When it happens

Trigger: An Accessible method calls into IAccessible with a self/child id that the native server rejects — e.g. enumerating children of a leaf element, using a stale child id after the element's children changed, or an upstream UIA cache/lookup passing an invalid childId.

Common situations: UIA clients walking child collections of MSAA-mapped controls while the control's child set changes (tree/list rebuilding); providers for controls that report children inconsistently; automation scripts that cache child elements across UI mutations.

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

• E_ACCESSDENIED
• E_OUTOFMEMORY
• E_UNEXPECTED
• name
• ArgumentOutOfRangeException (timeout was Duration.Automatic)

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/a6263d4bfaeee5bb. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/AutomationProxies/Accessible.cs:1356

                        // The object does not support the requested property or action. For example,
                        // a push button returns this value if you request its Value property, since
                        // it does not have a Value property.
                    case NativeMethods.E_NOTIMPL:
                        // just return on E_NOTIMPL errors
                        return false;

                    case NativeMethods.E_OUTOFMEMORY:
                        // Some OLEACC proxies produce out-of-memory for non-critical reasons:
                        // notably, the treeview proxy will raise this if the target HWND no longer exists,
                        // GetWindowThreadProcessID fails and it therefore won't be able to allocate shared
                        // memory in the target process, so it incorrectly assumes OOM.
                        throw new ElementNotAvailableException(e);
                        
                    case NativeMethods.E_INVALIDARG:
                        // One or more arguments were invalid. This error occurs when the caller attempts to identify
                        // a child object using an identifier that the server does not recognize. This error also results
                        // when a client attempts to identify a child object within an object that has no children.
                        throw new ArgumentException(SR.InvalidParameter);

                    case NativeMethods.E_ACCESSDENIED:
                        // This is returned when you call get_accValue to get the value of a password control.
                        throw new UnauthorizedAccessException();

                    case NativeMethods.E_UNEXPECTED:
                        // An IAccessible server has been released unexpectedly but still has pending events.
                        // If the current execution context is inside one of these event handlers it must be 
                        // abandoned.
                        throw new ElementNotAvailableException(e);

                    default:
                        // we want to know when we get an exception we haven't seen before
                        Debug.Fail(string.Format(CultureInfo.CurrentCulture, "MsaaNativeProvider: IAccessible threw a COMException: {0}", e.Message));
                        break;
                }
            }
            else if (e is InvalidCastException)

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