Converting RTF to HTML

Have you ever had the desire to convert some RTF text into HTML? Probably not. But if you do, then you are in luck! I recently had the need to do this conversion and after some searching found out a way to do it by enhancing a sample distributed in the MSDN library.  The sample is called: XAML to HTML Conversion Demo. 

The sample has code which converts HTML to and from a XAML Flow Document.  But this doesn’t make things easier until you realize that there is a way to convert RTF to XAML easily. The key is to use System.Windows.Controls.RichTextBox which can load RTF from a stream and save it as XAML.  This conversion is shown below:

         private static string ConvertRtfToXaml(string rtfText)

        {

            var richTextBox = new RichTextBox();

            if (string.IsNullOrEmpty(rtfText)) return "";

            var textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);

            using (var rtfMemoryStream = new MemoryStream())

            {

                using (var rtfStreamWriter = new StreamWriter(rtfMemoryStream))

                {

                    rtfStreamWriter.Write(rtfText);

                    rtfStreamWriter.Flush();

                    rtfMemoryStream.Seek(0, SeekOrigin.Begin);

                    textRange.Load(rtfMemoryStream, DataFormats.Rtf);

                }

            }

            using (var rtfMemoryStream = new MemoryStream())

            {

                textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);

                textRange.Save(rtfMemoryStream, DataFormats.Xaml);

                rtfMemoryStream.Seek(0, SeekOrigin.Begin);

                using (var rtfStreamReader = new StreamReader(rtfMemoryStream))

                {

                    return rtfStreamReader.ReadToEnd();

                }

            }

        }

With this code we have all we need to convert RTF to HTML. I modified the sample to add this RTF To XAML conversation and then I run that XAML through HTML converter which results in the HTML text. I added an interface to these conversion utilities and converted the sample into a library so that I would be able to use it from other projects.  Here is the interface:

  public interface IMarkupConverter

    {

        string ConvertXamlToHtml(string xamlText);

        string ConvertHtmlToXaml(string htmlText);

        string ConvertRtfToHtml(string rtfText);

    }

    public class MarkupConverter : IMarkupConverter

    {

        public string ConvertXamlToHtml(string xamlText)

        {

            return HtmlFromXamlConverter.ConvertXamlToHtml(xamlText, false);

        }

        public string ConvertHtmlToXaml(string htmlText)

        {

            return HtmlToXamlConverter.ConvertHtmlToXaml(htmlText, true);

        }

        public string ConvertRtfToHtml(string rtfText)

        {

            return RtfToHtmlConverter.ConvertRtfToHtml(rtfText);

        }

    }

With this I am now able to convert from RTF to HTML.  However, there is one catch - the conversion uses the RichTextBox WPF control which requires a single threaded apartment (STA).  Therefore in order to run your code that calls the ConvertRtfToHtml function, it must also be running in a STA.  If you can’t have your program run in a STA then you must create a new STA thread to run the conversion. Like this:

 MarkupConverter markupConverter = new MarkupConverter();

private string ConvertRtfToHtml(string rtfText)

{

   var thread = new Thread(ConvertRtfInSTAThread);

   var threadData = new ConvertRtfThreadData { RtfText = rtfText };

   thread.SetApartmentState(ApartmentState.STA);

   thread.Start(threadData);

   thread.Join();

   return threadData.HtmlText;

}

private void ConvertRtfInSTAThread(object rtf)

{

   var threadData = rtf as ConvertRtfThreadData;

   threadData.HtmlText = markupConverter.ConvertRtfToHtml(threadData.RtfText);

}

private class ConvertRtfThreadData

{

   public string RtfText { get; set; }

   public string HtmlText { get; set; }

}

Here is the zip contain the code for the Markup converter: MarkupConverter.zip

MarkupConverter.zip