dotnet/wpf · error · InvalidOperationException

throw new…

Error message

throw new InvalidOperationException(SR.OperationCannotBePerformed);

What it means

The WindowsPager proxy (an unsupported proxy for the Win32 pager control) implements IScrollProvider.SetScrollPercent. It throws InvalidOperationException(OperationCannotBePerformed) when IsScrollable() reports the pager has no scrollable content, so a scroll-percent operation cannot be performed.

Solutions

  1. Check the element's ScrollPattern.IsScrollable property (or IScrollProvider.GetIsScrollable) before calling SetScrollPercent
  2. Only call SetScrollPercent when the pager actually displays fewer than all of its content
  3. Catch InvalidOperationException and treat the element as non-scrollable / already at correct position

Example fix

// before
scrollPattern.SetScrollPercent(50);
// after
if (scrollPattern.Current.IsScrollable)
{
    scrollPattern.SetScrollPercent(50);
}
Defensive patterns

Strategy: validation

Validate before calling

if (!scrollPattern.Current.IsScrollable) return; // skip non-scrollable pager
scrollPattern.SetScrollPercent(pct, ScrollPattern.NoScroll);

Type guard

static bool CanScroll(AutomationElement el) =>
    el.TryGetCurrentPattern(ScrollPattern.Pattern, out var p) && ((ScrollPattern)p).Current.IsScrollable;

Try / catch

try { scrollPattern.SetScrollPercent(pct); }
catch (InvalidOperationException) { /* element not scrollable */ }

Prevention

When it happens

Trigger: Calling SetScrollPercent on a pager element whose IsScrollable() check fails — i.e. the control reports no scrollable range (after passing the enabled check).

Common situations: Automating a pager control that is fully showing its child (no scrolling needed), or querying scroll state before the pager has sized its content; also hit when binding ScrollPattern.SetScrollPercent to a non-scrollable pager.

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/5de022e0314554fe. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/UnsupportedAutomationProxies/windowspager.cs:253

            return null;
        }

        #endregion IRawElementProviderHwndOverride Interface 
    
        #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 (!IsScrollable())
            {
                throw new InvalidOperationException(SR.OperationCannotBePerformed);
            }

            bool fHorizontal = IsHorizontal(_hwnd);

            // Can scroll either horizontally or vertically, but not both. Sanity check
            if ((fHorizontal && (int)verticalPercent != (int)ScrollPattern.NoScroll) || 
                (!fHorizontal && (int)horizontalPercent != (int)ScrollPattern.NoScroll))
            {
                throw new InvalidOperationException(SR.OperationCannotBePerformed);
            }

            if (!ScrollByPercent(fHorizontal ? horizontalPercent : verticalPercent))
            {
                throw new InvalidOperationException(SR.OperationCannotBePerformed);
            }
        }

        // Request to scroll horizontally and vertically by the specified scrolling amount

View on GitHub (pinned to 81131a70a4)