dotnet/wpf · error

ScrollViewer marked as PART_ContentHost must have no…

Error message

ScrollViewer marked as PART_ContentHost must have no content.

What it means

When PasswordBox applies its control template, SetRenderScopeToContentHost attaches the internal PasswordTextBox render scope to the PART_ContentHost element. If that part is a ScrollViewer that already has Content, WPF throws NotSupportedException because the content host must be empty to host the password render scope.

Solutions

1. Remove all content from the PART_ContentHost ScrollViewer in the template
2. Add watermarks/hints as sibling elements overlaying the content host, not as its Content
3. Use TemplateBinding-free, empty ScrollViewer exactly named PART_ContentHost with ScrollViewer.Content = null
4. Base the custom template on the stock PasswordBox template rather than the TextBox one

Example fix

// before
<ScrollViewer x:Name="PART_ContentHost">
  <TextBlock Text="Enter password"/> <!-- throws -->
</ScrollViewer>
// after
<Grid>
  <ScrollViewer x:Name="PART_ContentHost"/>
  <TextBlock Text="Enter password" IsHitTestVisible="False" Visibility="{Binding Text, Converter=...}"/>
</Grid>

var sv = templateChild as ScrollViewer;
bool ok = sv != null && sv.Content == null; // PART_ContentHost must be an empty ScrollViewer

bool isEmptyContentHost(FrameworkElement fe) =>
    (fe is ScrollViewer sv && sv.Content == null) || (fe is Decorator d && d.Child == null);

When it happens

Trigger: A custom PasswordBox ControlTemplate whose ScrollViewer named PART_ContentHost contains child content (elements or inline content set on ScrollViewer.Content), triggering template application (InitializeRenderScope).

Common situations: Copying a TextBox template and adding decorations inside the PART_ContentHost ScrollViewer; blending a TextBlock watermark inside the content host; hand-edited templates after upgrading from a TextBox template.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Decorator marked as PART_ContentHost must have no content.
• Only Decorator and ScrollViewer can be used as…
• ElementNotEnabledException
• InvalidOperationException (no message)
• InvalidOperationException

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/46b6bde25112faf4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/PasswordBox.cs:940

        {
            // Clear the content host from previous render scope (if any)
            ClearContentHost();

            // Find ContentHostTemplateName in the style
            _passwordBoxContentHost = GetTemplateChild(ContentHostTemplateName) as FrameworkElement;

            // Note that we allow ContentHostTemplateName to be optional.
            // This simplifies toolability of our control styling.
            // When the ContentHostTemplateName is not found or incorrect
            // PasswordBox goes into disabled state, but does not throw.

            // Add renderScope as a child of ContentHostTemplateName
            _renderScope = renderScope;
            if (_passwordBoxContentHost is ScrollViewer scrollViewer)
            {
                if (scrollViewer.Content != null)
                {
                    throw new NotSupportedException(SR.TextBoxScrollViewerMarkedAsTextBoxContentMustHaveNoContent);
                }
                else
                {
                    scrollViewer.Content = _renderScope;
                }
            }
            else if (_passwordBoxContentHost is Decorator decorator)
            {
                if (decorator.Child != null)
                {
                    throw new NotSupportedException(SR.TextBoxDecoratorMarkedAsTextBoxContentMustHaveNoContent);
                }
                else
                {
                    decorator.Child = _renderScope; // this may replace old render scope in case of upgrade scenario in TextBox
                }
            }
            else

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