dotnet/wpf · error · ArgumentException

SR.Format(SR.UnexpectedParameterType, value.GetType()…

Error message

SR.Format(SR.UnexpectedParameterType, value.GetType(), typeof(TableCellStructure))

What it means

This ArgumentException is thrown by TableCellStructure.AddChild when the child object is not a TableCellStructure-accepted block element. Cells only accept block-level structure children (ParagraphStructure, TableStructure, ListStructure, FigureStructure) per the XPS schema implemented by this container's twin (see index 2664 pattern in the same file).

Solutions

Add only ParagraphStructure/TableStructure/ListStructure/FigureStructure instances to the cell
Wrap inline content in a ParagraphStructure before adding
Check the actual runtime type in the exception message
Guard with a type check before AddChild

Example fix

// before
cell.AddChild("some text");
// after
var para = new ParagraphStructure();
cell.Blocks.Add(para);

Defensive patterns

Strategy: type-guard

Validate before calling

if (value is not (ParagraphStructure or TableStructure or ListStructure or FigureStructure)) throw new ArgumentException("Cell does not accept this child type");

Type guard

bool IsCellBlock(object o) => o is ParagraphStructure || o is TableStructure || o is ListStructure || o is FigureStructure;

Try / catch

try { cellAddChild(value); } catch (ArgumentException ex) { /* inspect ex.Message for the bad type */ }

Prevention

Wrap inline content in ParagraphStructure before adding to cells
Never add rows/row-groups to a cell
Prefer the typed Blocks collection

When it happens

Trigger: Calling AddChild on TableCellStructure with an object that fails the accepted-type test — e.g. a Run, a TextBlock, or a TableRowStructure.

Common situations: Putting inline flow content directly into cells; converting FixedDocument flow code to document-structure code without wrapping content.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9643ee41ea63f621. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/DocumentStructures/SemanticBasicElement.cs:381

        public TableRowStructure()
        {
            _elementType = FixedElement.ElementType.TableRow;
        }

        public void Add(TableCellStructure tableCell)
        {
            ArgumentNullException.ThrowIfNull(tableCell);
            ((IAddChild) this).AddChild(tableCell);
        }
    
        void IAddChild.AddChild(object value)
        {
            if (value is TableCellStructure)
            {
                _elementList.Add((TableCellStructure)value);
                return;
            }
            throw new ArgumentException(SR.Format(SR.UnexpectedParameterType, value.GetType(), typeof(TableCellStructure)), nameof(value));
        }
        
        void IAddChild.AddText(string text) { }
        
        IEnumerator<TableCellStructure> IEnumerable<TableCellStructure>.GetEnumerator()
        {
            throw new NotSupportedException();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IEnumerable<TableCellStructure>)this).GetEnumerator();
        }
    }

    /// <summary>
    ///
    /// </summary>

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