dotnet/wpf · error · InvalidOperationException

SR.TextSchema_ChildTypeIsInvalid (parent type name, child…

Error message

SR.TextSchema_ChildTypeIsInvalid (parent type name, child type name)

What it means

ValidateChild(TextElement parent, TextElement child, ...) checks whether the child element's type is a legal child of the parent's type per the WPF text schema (Table 2: Paragraph can contain Inline, etc.). If it is not and throwIfIllegalChild is true, an InvalidOperationException naming both type names is thrown. This guards the document tree from schema-invalid parent/child relationships.

Solutions

1. Check TextSchema.IsValidChild(parent, child) before adding the element
2. Restructure: wrap Block children in Paragraph (or use an Inline-compat wrapper) so the parent/child pair matches the schema, e.g. Span can only contain Inline
3. Use the correct container type for the child (e.g. use Paragraph instead of Span when adding Block content)
4. Catch InvalidOperationException and inspect the two type names in the message to correct the hierarchy

Example fix

// before
Span span = new Span();
span.Inlines.Add(new Paragraph(new Run("x"))); // invalid: Paragraph is a Block
// after
Paragraph p = new Paragraph();
p.Inlines.Add(new Run("x"));
// or: BlockUIContainer / Section for block content

if (!TextSchema.IsValidChild(parent, child)) throw new ArgumentException($"{child.GetType().Name} cannot be a child of {parent.GetType().Name}");

static bool IsLegalChild(TextElement parent, TextElement child) => TextSchema.IsValidChild(parent.GetType(), child.GetType());

try { parent.Inlines.Add(child); } catch (InvalidOperationException ex) when (ex.Message.Contains("ChildTypeIsInvalid")) { /* restructure tree */ }

When it happens

Trigger: Adding a TextElement of an illegal type to a parent, e.g. appending a Paragraph to a Span, inserting a Table inside a Hyperlink, adding a Run directly to a FlowDocument, or TextRange/selection edits that would produce such a combination.

Common situations: Building FlowDocuments in code with wrong nesting (Block inside Inline container); pasting content whose structure doesn't fit; custom editors applying text element types to the wrong container.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• SR.TextSchema_ChildTypeIsInvalid (parent type name…
• SR.TableCollectionInOtherCollection
• SR.TextSchema_IllegalHyperlinkChild (childType)
• " }} " element found. Expected fixed page element ( }} ).
• ' ' can only host a ' ' or a ' '. ' ' is an invalid…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/afaf7d667789ebbc. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/TextSchema.cs:113

        {
            return ValidateChild(parent, child, false /* throwIfIllegalChild */, false /* throwIfIllegalHyperlinkDescendent */);
        }
#endif

        internal static bool ValidateChild(TextElement parent, TextElement child, bool throwIfIllegalChild, bool throwIfIllegalHyperlinkDescendent)
        {
            // Disallow nested hyperlink elements.
            if (TextSchema.HasHyperlinkAncestor(parent) &&
                TextSchema.HasIllegalHyperlinkDescendant(child, throwIfIllegalHyperlinkDescendent))
            {
                return false;
            }

            bool isValidChild = IsValidChild(parent.GetType(), child.GetType());

            if (!isValidChild && throwIfIllegalChild)
            {
                throw new InvalidOperationException(SR.Format(SR.TextSchema_ChildTypeIsInvalid, parent.GetType().Name, child.GetType().Name));
            }

            return isValidChild;
        }

        internal static bool IsValidChild(TextElement parent, Type childType)
        {
            return ValidateChild(parent, childType, false /* throwIfIllegalChild */, false /* throwIfIllegalHyperlinkDescendent */);
        }

        internal static bool ValidateChild(TextElement parent, Type childType, bool throwIfIllegalChild, bool throwIfIllegalHyperlinkDescendent)
        {
            // Disallow nested hyperlink elements.
            if (TextSchema.HasHyperlinkAncestor(parent))
            {
                if (typeof(Hyperlink).IsAssignableFrom(childType) ||
                    typeof(AnchoredBlock).IsAssignableFrom(childType))
                {

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