Error in System.Windows.Control.RichTextBox

Question

Error in System.Windows.Control.RichTextBox

I am creating a control in WPF that shows units using System.Windows.Control.RichTextBox.

The problem is that the RichTextBox control displays plain text instead of rich text. I think the RichTextBox control has an error, and I don’t know how to do it, because it works depending on the computer.

XAML Code,

<RichTextBox x:FieldModifier="private"
             x:Name="TxtItem1"
             IsReadOnly="True"
             IsHitTestVisible="False"
             HorizontalContentAlignment="Center"
             VerticalContentAlignment="Center" />

And the piece of code behind:

private static void UpdateDocument(RichTextBox control, DependencyPropertyChangedEventArgs e)
{
    string content = e.NewValue as string;
    control.Document = content.Html1ToFlowDocument();
}

The Html1ToFlowDocument function converts a string to a FlowDocument. The following image is on a computer in which the code works fine (Windows 7 64 bit):

GOES

And the following does not work (Windows 7 64 bit):

WRONG

Another approach was to use RTF text, but I have a problem.

Html1ToFlowDocument function code,

public static class Html1ToDocument
{
    public static FlowDocument Html1ToFlowDocument(this string text)
    {
        var mcFlowDoc = new FlowDocument();

        XmlDocument doc = new XmlDocument();
        doc.LoadXml(string.Format("<P>{0}</P>", text));

        XmlElement root = doc.GetElementsByTagName("P")[0] as XmlElement;

        IEnumerable<Inline> children;
        try
        {
            children = ParseChildren(root);
        }
        catch (Exception ex)
        {
            throw new FormatException("Unsupported text.", ex);
        }

        var paragraph = new Paragraph();
        paragraph.Inlines.AddRange(children);

        mcFlowDoc.Blocks.Add(paragraph);
        return mcFlowDoc;
    }

    private static IEnumerable<Inline> ParseChildren(XmlElement root)
    {
        Span sitem;
        List<Inline> children;

        foreach (XmlNode element in root.ChildNodes)
        {
            Inline item = null;
            if (element is XmlElement)
            {
                XmlElement xelement = (XmlElement)element;
                switch (xelement.Name.ToUpper())
                {
                    case "SUB":
                        children = ParseChildren(xelement).ToList();
                        if (children.Count == 1 && children.First() is Run)
                        {
                            item = children.First();
                            item.Typography.Variants = FontVariants.Subscript;
                        }
                        else
                        {
                            sitem = new Span();
                            sitem.Typography.Variants = FontVariants.Subscript;
                            sitem.Inlines.AddRange(children);
                            item = sitem;
                        }

                        break;
                    case "SUPER":
                        children = ParseChildren(xelement).ToList();
                        if (children.Count == 1 && children.First() is Run)
                        {
                            item = children.First();
                            item.Typography.Variants = FontVariants.Superscript;
                        }
                        else
                        {
                            sitem = new Span();
                            sitem.Typography.Variants = FontVariants.Superscript;
                            sitem.Inlines.AddRange(children);
                            item = sitem;
                        }
                        break;
                }

                yield return item;
            }
            else if (element is XmlText)
            {
                item = new Run(element.InnerText);
                yield return item;
            }
        }
    }
}