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DeferredControls.md

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Deferred Controls

Some ASP.NET Web Forms controls have been permanently deferred from implementation in this library. This page documents each deferred control, explains why it's excluded, and provides recommended alternatives for your Blazor migration.

Chart — Implemented

!!! success "Chart is FULLY IMPLEMENTED" The Chart component has been implemented with Chart.js and supports 8 chart types: Column, Bar, Line, Pie, Area, Doughnut, Scatter (Point), and StackedColumn. See the Chart documentation for full details.

Unsupported Chart Types

The following 27 chart types from the Web Forms SeriesChartType enum are not supported and will throw NotSupportedException. If your application uses any of these, you will need an alternative approach:

Chart Type Alternative
Stock, Candlestick Use a dedicated financial charting library (e.g., Lightweight Charts)
Bubble Can be approximated with a scatter chart and custom point sizes via Chart.js plugins
Radar, Polar Chart.js supports these natively — consider a Chart.js plugin or custom integration
Funnel, Pyramid Use a dedicated visualization library or custom SVG
Spline, SplineArea, SplineRange Use Line/Area as an approximation; Chart.js tension options can create curved lines
StackedBar, StackedArea, StackedColumn100, StackedBar100, StackedArea100 Use StackedColumn or Bar as a starting point; full stacking support may be added in a future release
Range, RangeBar, RangeColumn Use a dedicated charting library for range-style visualizations
BoxPlot, ErrorBar Use a statistical charting library
Renko, ThreeLineBreak, Kagi, PointAndFigure Specialized financial chart types — use a dedicated financial charting library
FastPoint, FastLine, StepLine Use Point or Line respectively; Chart.js handles performance optimization automatically

Substitution — Implemented

!!! success "Substitution is IMPLEMENTED" The Substitution component has been implemented as a migration compatibility component. In Web Forms, Substitution provided post-cache substitution; in Blazor, it renders callback output directly since all rendering is dynamic. See the Substitution documentation for full details.

Xml

Original Microsoft documentation: https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.xml?view=netframework-4.8

What It Did in Web Forms

The <asp:Xml> control displayed the contents of an XML document or the results of an XSLT transformation. It could take an XML source (inline, from a file, or from a System.Xml.XmlDocument) and optionally transform it using an XSLT stylesheet before rendering the output.

<asp:Xml ID="XmlDisplay" runat="server"
         DocumentSource="~/App_Data/catalog.xml"
         TransformSource="~/App_Data/catalog.xslt" />

Or with inline XML:

<asp:Xml ID="XmlInline" runat="server"
         TransformSource="~/App_Data/transform.xslt">
    <book>
        <title>Blazor in Action</title>
        <author>Chris Sainty</author>
    </book>
</asp:Xml>

Why It's Not Implemented

XSLT transforms via <asp:Xml> are a legacy pattern with near-zero adoption in modern projects:

  • XSLT is rarely used in new development — it has been superseded by direct data binding, JSON APIs, and component-based rendering
  • The control existed for a very specific early-2000s pattern of XML-driven content rendering that has no meaningful migration demand
  • Building an XSLT transformation engine as a Blazor component would add complexity for a feature almost no one migrating to Blazor will need

What to Do Instead

Replace with direct data binding or Razor markup. If your Web Forms application used <asp:Xml> to display structured data, the Blazor equivalent is simply binding that data to components or HTML directly.

Before (Web Forms — XML + XSLT to render a list):

<asp:Xml ID="BookList" runat="server"
         DocumentSource="~/App_Data/books.xml"
         TransformSource="~/App_Data/books.xslt" />
<!-- books.xml -->
<books>
    <book><title>Blazor in Action</title><author>Chris Sainty</author></book>
    <book><title>ASP.NET Core in Action</title><author>Andrew Lock</author></book>
</books>
<!-- books.xslt -->
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/books">
        <ul>
            <xsl:for-each select="book">
                <li><xsl:value-of select="title"/> by <xsl:value-of select="author"/></li>
            </xsl:for-each>
        </ul>
    </xsl:template>
</xsl:stylesheet>

After (Blazor — direct data binding):

<ul>
    @foreach (var book in books)
    {
        <li>@book.Title by @book.Author</li>
    }
</ul>

@code {
    private List<Book> books;

    protected override void OnInitialized()
    {
        books = BookService.GetBooks();
    }
}

!!! tip "If you genuinely need XSLT in Blazor" If your application logic truly depends on XSLT transformations (e.g., you receive XML from a third-party system and must apply an XSLT stylesheet), you can still use System.Xml.Xsl.XslCompiledTransform in your C# code and render the result as a MarkupString:

```razor
@((MarkupString)transformedHtml)

@code {
    private string transformedHtml;

    protected override void OnInitialized()
    {
        var xslt = new XslCompiledTransform();
        xslt.Load("transform.xslt");

        using var writer = new StringWriter();
        xslt.Transform("source.xml", null, writer);
        transformedHtml = writer.ToString();
    }
}
```

This approach keeps the XSLT logic in C# where it belongs, rather than embedding it in a UI control.

Summary

Control Status Recommendation
Chart ✅ Complete Implemented with 8 chart types via Chart.js. Unsupported types need alternative libraries.
Substitution ✅ Complete Implemented — renders callback output directly. Post-cache substitution not applicable in Blazor.
Xml ❌ Deferred Use XDocument + data binding or XslCompiledTransform + MarkupString

See Also