dotnet/wpf · error · InvalidOperationException

SR.UIA_OperationCannotBePerformed

Error message

SR.UIA_OperationCannotBePerformed

What it means

GridSplitterAutomationPeer explicitly rejects resizing: ITransformProvider.Resize always throws InvalidOperationException(SR.UIA_OperationCannotBePerformed). The peer reports CanResize=false, and UIA convention is to throw this exception if a client still attempts the unsupported operation.

Solutions

  1. Do not call Resize on GridSplitter; check CanResize first and skip when false.
  2. Set the splitter's resize behavior via ResizeDirection/ResizeBehavior properties in XAML instead of the UIA Transform pattern.
  3. Catch InvalidOperationException from Resize and treat as operation-not-supported.
  4. Use the Grid's ColumnDefinition/RowDefinition manipulation (e.g. GridResizeBehavior) as the supported resizing mechanism.

Example fix

// before
((ITransformProvider)peer).Resize(120, 30);
// after
if (((ITransformProvider)peer).CanResize) ((ITransformProvider)peer).Resize(120, 30);
else splitter.ResizeDirection = GridResizeDirection.Columns;
Defensive patterns

Strategy: validation

Validate before calling

if (!((ITransformProvider)peer).CanResize) throw new NotSupportedException("GridSplitter cannot be resized via Transform pattern");

Try / catch

try { ((ITransformProvider)peer).Resize(w, h); }
catch (InvalidOperationException) { /* unsupported: use XAML resize behavior */ }

Prevention

When it happens

Trigger: A UIA client calls ITransformProvider.Resize on a GridSplitter element despite the Transform pattern's CanResize property being false.

Common situations: Generic test drivers that invoke every pattern method without checking capability properties like CanResize; tools recording and replaying transform operations on elements whose capabilities differ.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/8add38d760d9d7cb. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/GridSplitterAutomationPeer.cs:52

        bool ITransformProvider.CanResize { get { return false; } }
        bool ITransformProvider.CanRotate { get { return false; } }

        void ITransformProvider.Move(double x, double y)
        {
            if (!IsEnabled())
                throw new ElementNotEnabledException();

            if (double.IsInfinity(x) || double.IsNaN(x))
                throw new ArgumentOutOfRangeException(nameof(x));

            if (double.IsInfinity(y) || double.IsNaN(y))
                throw new ArgumentOutOfRangeException(nameof(y));

            ((GridSplitter)Owner).KeyboardMoveSplitter(x, y);
        }
        void ITransformProvider.Resize(double width, double height)
        {
            throw new InvalidOperationException(SR.UIA_OperationCannotBePerformed);
        }
        void ITransformProvider.Rotate(double degrees)
        {
            throw new InvalidOperationException(SR.UIA_OperationCannotBePerformed);
        }

        #endregion
    }
}

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