What causes "SR.FrameNoAddChild" in dotnet/wpf?

Set frame.Source = new Uri("Page1.xaml", UriKind.Relative) instead of adding children.

dotnet/wpf · error · InvalidOperationException

SR.FrameNoAddChild

Error message

SR.FrameNoAddChild

What it means

Frame overrides AddChild and unconditionally throws this InvalidOperationException: a Frame does not support object children. Navigation content is supplied through the Source property or Navigate(), not by adding child elements, so XAML child elements inside <Frame> are rejected.

Solutions

Set frame.Source = new Uri("Page1.xaml", UriKind.Relative) instead of adding children.
Use frame.Navigate(pageOrUri) to display content.
If you only need static hosted content without navigation, use a ContentControl or similar container instead of Frame.

Example fix

<!-- before: throws -->
<Frame>
  <TextBlock Text="hello"/>
</Frame>

<!-- after -->
<Frame Source="Page1.xaml"/>
<!-- or -->
<ContentControl>
  <TextBlock Text="hello"/>
</ContentControl>

Defensive patterns

Strategy: validation

Validate before calling

// Never add children to Frame; set content via Source/Navigate.
if (content is Uri uri) frame.Source = uri;
else frame.Navigate(content);

Try / catch

try { frame.AddChild(value); }
catch (InvalidOperationException) { frame.Navigate(value); }

Prevention

Use Frame.Source or Frame.Navigate for content; never nest child elements in <Frame>.
Use ContentControl when static embedded content is what you need.
Grep XAML for inner elements inside Frame tags during migration from other containers.

When it happens

Trigger: Declaring child elements directly inside <Frame>...</Frame> in XAML, or calling frame.AddChild(...) / AddText programmatically.

Common situations: Migrating markup from another ContentControl (e.g. swapping a ContentControl for a Frame but keeping inner elements); trying to embed static content in a Frame instead of using Source="page.xaml" or Navigate.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/41a98f2380dbde2b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Frame.cs:537

        //  Protected Methods
        //
        //------------------------------------------------------
        #region Protected Methods

        /// <summary>
        /// Creates AutomationPeer (<see cref="UIElement.OnCreateAutomationPeer"/>)
        /// </summary>
        protected override AutomationPeer OnCreateAutomationPeer()
        {
            return new FrameAutomationPeer(this);
        }

        /// <summary>
        ///  Add an object child to this control
        /// </summary>
        protected override void AddChild(object value)
        {
            throw new InvalidOperationException(SR.FrameNoAddChild);
        }

        /// <summary>
        ///  Add a text string to this control
        /// </summary>
        protected override void AddText(string text)
        {
            XamlSerializerUtil.ThrowIfNonWhiteSpaceInAddText(text, this);
        }
        #endregion

        #region Event Handlers

        private void _OnBPReady(Object o, BPReadyEventArgs e)
        {
            // update content property
            SetCurrentValueInternal(ContentProperty, e.Content);

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