dotnet/wpf · error · ElementNotAvailableException

ElementNotAvailableException

Error message

ElementNotAvailableException

What it means

WindowsCalendar.MakeReadyForInput() throws ElementNotAvailableException when the native calendar hwnd is not visible (SafeNativeMethods.IsWindowVisible(_hwnd) is false). In UIA, an element whose backing window has disappeared or is hidden is considered no longer available.

Solutions

1. Ensure the calendar window is visible before performing the operation (show the form / select the tab).
2. Re-find the element and retry; a stale reference to a hidden or recreated control triggers this.
3. Handle ElementNotAvailableException in the UIA client and refresh the element from the automation tree.
4. Avoid automating controls on minimized or closed windows.

Example fix

// before
invokePattern.SetValue(dateText);
// after
if (calendarElement.Current.IsOffscreen == false)
{
    invokePattern.SetValue(dateText);
}
else
{
    calendarElement = treeWalker.GetParent(...); // refresh/re-find the element
}

if (calendarElement != null && !calendarElement.Current.IsOffscreen) { /* proceed */ }

static bool IsAlive(AutomationElement e) { try { var _ = e.Current.Name; return true; } catch (ElementNotAvailableException) { return false; } }

try { /* calendar input operation */ } catch (ElementNotAvailableException) { calendarElement = ReFindElement(); /* then retry */ }

When it happens

Trigger: Any calendar provider operation that requires input preparation (e.g. setting focus/selection) while the MonthCalendar window is hidden, on a background tab, or its parent window is minimized/closed.

Common situations: UIA scripts automating a calendar on a hidden form, a form that was closed between element lookup and invocation (stale element), or controls hidden by tabbed layouts.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• E_OUTOFMEMORY
• Element no longer available.
• Element no longer available.
• ElementNotAvailableException
• ElementNotAvailableException

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/b26ec1af39fbdc25. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/UnsupportedAutomationProxies/WindowsCalendar.cs:2211

                    }
                }
            }

            // Detect if we're in the menu mode.
            private bool InCalendarMenuMode()
            {
                NativeMethods.GUITHREADINFO gui;
                uint processId;
                uint threadId = Misc.GetWindowThreadProcessId(_hwnd, out processId);
                return (Misc.ProxyGetGUIThreadInfo(threadId, out gui)
                            && (Misc.IsBitSet(gui.dwFlags, NativeMethods.GUI_POPUPMENUMODE)));
            }

            private bool MakeReadyForInput()
            {
                if (!SafeNativeMethods.IsWindowVisible(_hwnd))
                {
                    throw new ElementNotAvailableException();
                }

                NativeMethods.GUITHREADINFO gui;

                if (Misc.ProxyGetGUIThreadInfo(0, out gui) && _hwnd == gui.hwndActive)
                {
                    return true;
                }

                // try to set focus
                return Misc.SetFocus(_hwnd);
            }

            #endregion ExpandCollapse Helper

            #endregion
        }

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