dotnet/wpf · error · InvalidOperationException

SR.OperationCannotBePerformed

Error message

SR.OperationCannotBePerformed

What it means

The WindowsCalendar proxy cannot scroll vertically: if verticalPercent is anything other than ScrollPattern.NoScroll, SetScrollPercent throws InvalidOperationException(SR.OperationCannotBePerformed). The month calendar supports only horizontal scrolling.

Solutions

  1. Pass ScrollPattern.NoScroll for verticalPercent and only scroll horizontally.
  2. Query VerticalScrollPercent first; if it reports NoScroll, skip the vertical axis.
  3. Catch InvalidOperationException and handle vertical scrolling via another mechanism (keyboard/selection).

Example fix

// before
scrollPattern.SetScrollPercent(50, 50);
// after
scrollPattern.SetScrollPercent(50, ScrollPattern.NoScroll);
Defensive patterns

Strategy: validation

Validate before calling

if ((int)verticalPercent != (int)ScrollPattern.NoScroll)
    throw new InvalidOperationException("WindowsCalendar does not support vertical scrolling");

Type guard

bool SupportsVerticalScroll(IScrollProvider sp) => sp.VerticalScrollPercent != ScrollPattern.NoScroll;

Try / catch

try { scrollPattern.SetScrollPercent(h, v); }
catch (InvalidOperationException) { /* vertical not supported; scroll horizontally only */ }

Prevention

When it happens

Trigger: Calling IScrollProvider.SetScrollPercent with a verticalPercent other than ScrollPattern.NoScroll (e.g. 50) on a month-calendar element.

Common situations: Generic scroll automation scripts that set both axes on every control; assuming the calendar behaves like a scrollable list.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/35094066db1ec5c9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/UnsupportedAutomationProxies/WindowsCalendar.cs:359

            return base.ElementProviderFromPoint (x, y);
        }

        #endregion

        #region Scroll Pattern

        // Request to scroll Horizontally and vertically by the specified amount
        void IScrollProvider.SetScrollPercent (double horizontalPercent, double verticalPercent)
        {
            // Make sure that the control is enabled
            if (!SafeNativeMethods.IsWindowEnabled(_hwnd))
            {
                throw new ElementNotEnabledException();
            }

            if ((int)verticalPercent != (int)ScrollPattern.NoScroll)
            {
                throw new InvalidOperationException(SR.OperationCannotBePerformed);
            }
            else if ((int)horizontalPercent == (int)ScrollPattern.NoScroll)
            {
                return;
            }
            else if (horizontalPercent < 0 || horizontalPercent > 100)
            {
                throw new ArgumentOutOfRangeException("horizontalPercent", SR.ScrollBarOutOfRange);
            }

            int cDisplayedMonths = GetMonthCount();
            DateTime [] dateRange =
                CreateDateTimeFromSystemTime (GetRawValue (_hwnd, CalendarData.Range));
            int cMonths = (dateRange [1].Year - dateRange [0].Year) * 12
                            + (dateRange [1].Month - dateRange [0].Month) + 1;

            if (cMonths <= cDisplayedMonths)
            {

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