dotnet/wpf · error · InvalidOperationException

SR.DataGrid_CannotSelectCell

Error message

SR.DataGrid_CannotSelectCell

What it means

DataGridCellItemAutomationPeer's ISelectionItemProvider.AddToSelection can only add cells to selection when the DataGrid's SelectionUnit is Cell (or cell-level selection is meaningful). If the DataGrid is not in cell selection mode, the peer throws InvalidOperationException with SR.DataGrid_CannotSelectCell because full-row selection cannot accommodate cell-based selection requests.

Solutions

1. Set DataGrid.SelectionUnit="Cell" when cell-level automation selection is required.
2. Change the automation client to use row/row-item selection patterns when SelectionUnit is FullRow.
3. Catch InvalidOperationException and fall back to selecting the row containing the cell.
4. Check SelectionUnit before invoking selection APIs in test code.

Example fix

// before
cellSelectionItem.AddToSelection();

// after
if (dataGrid.SelectionUnit == DataGridSelectionUnit.Cell)
    cellSelectionItem.AddToSelection();
else
    rowSelectionItem.Select();

bool canAdd = dataGrid.SelectionUnit == DataGridSelectionUnit.Cell;

try { peer.AddToSelection(); } catch (InvalidOperationException) { rowPeer.Select(); }

When it happens

Trigger: An automation client calls AddToSelection() on a DataGrid cell while DataGrid.SelectionUnit is FullRow (or the peer's IsCellSelectionUnit check fails for another reason such as a shared/placeholder item).

Common situations: UIA tests written against DataGrids configured with SelectionUnit="Cell" being run against one with SelectionUnit="FullRow" (default); theme or control-template changes; automated accessibility tooling selecting cells.

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

• Can only call SelectAll when CanSelectMultipleItems is true.
• SR.DataGrid_AutomationInvokeFailed
• SR.DataGrid_CannotSelectCell
• SR.DataGrid_ColumnIsReadOnly
• SR.DataGridColumnHeaderItemAutomationPeer_Unresizable

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/a723d478dae811d8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Automation/Peers/DataGridCellItemAutomationPeer.cs:687

            get
            {
                return this.OwningDataGrid.SelectedCellsInternal.Contains(new DataGridCellInfo(Item, _column));
            }
        }

        IRawElementProviderSimple ISelectionItemProvider.SelectionContainer
        {
            get
            {
                return this.ContainingGrid;
            }
        }

        void ISelectionItemProvider.AddToSelection()
        {
            if (!IsCellSelectionUnit)
            {
                throw new InvalidOperationException(SR.DataGrid_CannotSelectCell);
            }

            // If item is already selected - do nothing
            DataGridCellInfo currentCellInfo = new DataGridCellInfo(Item, _column);
            if (this.OwningDataGrid.SelectedCellsInternal.Contains(currentCellInfo))
            {
                return;
            }

            EnsureEnabled();

            if (this.OwningDataGrid.SelectionMode == DataGridSelectionMode.Single &&
                this.OwningDataGrid.SelectedCells.Count > 0)
            {
                throw new InvalidOperationException();
            }

            this.OwningDataGrid.SelectedCellsInternal.Add(currentCellInfo);

View on GitHub (pinned to 81131a70a4)