Specified index is out of range or child at index is null…

Error message

Specified index is out of range or child at index is null. Do not call this method if VisualChildrenCount returns zero, indicating that the Visual has no children.

What it means

GridViewRowPresenterBase.GetVisualChild(index) throws ArgumentOutOfRangeException when the presenter has no internal UIElementCollection (no child rows have been created). The API contract forbids calling GetVisualChild when VisualChildrenCount is zero; this implementation additionally indexes the collection directly, so an out-of-range index also throws.

Solutions

Check VisualChildrenCount > 0 before calling GetVisualChild
Defer visual-tree inspection until the presenter is loaded and realized (e.g. Loaded event)
Use VisualTreeHelper.GetChild within the reported count instead of fixed indexes

Example fix

// before
var child = rowPresenter.GetVisualChild(0);
// after
if (rowPresenter.VisualChildrenCount > 0)
    var child = rowPresenter.GetVisualChild(0);

Defensive patterns

Strategy: validation

Validate before calling

if (presenter.VisualChildrenCount > 0 && index < presenter.VisualChildrenCount) { var c = presenter.GetVisualChild(index); }

Type guard

static bool CanGetChild(System.Windows.Controls.Primitives.GridViewRowPresenterBase p, int i) => i >= 0 && i < p.VisualChildrenCount;

Try / catch

try { var child = presenter.GetVisualChild(index); }
catch (ArgumentOutOfRangeException) { /* presenter not realized yet or bad index */ }

Prevention

Defer visual-tree inspection until after Loaded/layout
Never assume the presenter has children; check the count
Use VisualTreeHelper.GetChild with the dynamic count

When it happens

Trigger: Calling GetVisualChild on a GridViewRowPresenterBase-derived presenter (e.g. GridViewRowPresenter/GridViewHeaderRowPresenter) before its items/columns have created the UIElementCollection, or with an index outside the collection's Count.

Common situations: Visual-tree inspection during a layout pass before the ListView's items are realized, or hard-coded child indexes when templating ListView/GridView.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/0ed2d3f5445499ca. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/GridViewRowPresenterBase.cs:125

                if (_uiElementCollection == null)
                {
                    return 0;
                }
                else
                {
                    return _uiElementCollection.Count;
                }
            }
        }

        /// <summary>
        /// Gets the Visual child at the specified index.
        /// </summary>
        protected override Visual GetVisualChild(int index)
        {
            if (_uiElementCollection == null)
            {
                throw new ArgumentOutOfRangeException(nameof(index), index, SR.Visual_ArgumentOutOfRange);
            }
            return _uiElementCollection[index];
        }

        #endregion

        //-------------------------------------------------------------------
        //
        // Internal Methods / Properties
        //
        //-------------------------------------------------------------------

        #region Internal Methods

        /// <summary>
        /// process the column collection chagned event
        /// </summary>
        internal virtual void OnColumnCollectionChanged(GridViewColumnCollectionChangedEventArgs e)

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