Qt5. Вставить объект QWidget в QML

Я столкнулся с тем же вопросом. В конце я вышел с обычным автором:

public class IndentTextXmlWriter : XmlTextWriter
{
    private int indentLevel;
    private bool isInsideAttribute;

    public IndentTextXmlWriter(TextWriter textWriter): base(textWriter)
    {
    }

    public bool IndentText { get; set; }

    public override void WriteStartAttribute(string prefix, string localName, string ns)
    {
        isInsideAttribute = true;
        base.WriteStartAttribute(prefix, localName, ns);
    }

    public override void WriteEndAttribute()
    {
        isInsideAttribute = false;
        base.WriteEndAttribute();
    }

    public override void WriteStartElement(string prefix, string localName, string ns)
    {
        indentLevel++;
        base.WriteStartElement(prefix, localName, ns);
    }

    public override void WriteEndElement()
    {
        indentLevel--;
        base.WriteEndElement();
    }

    public override void WriteString(string text)
    {
        if (String.IsNullOrEmpty(text) || isInsideAttribute || Formatting != Formatting.Indented || !IndentText || XmlSpace == XmlSpace.Preserve)
        {
            base.WriteString(text);
            return;
        }

        string[] lines = text.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
        string indent = new string(IndentChar, indentLevel * Indentation);
        foreach (string line in lines)
        {
            WriteRaw(Environment.NewLine);
            WriteRaw(indent);
            WriteRaw(line.Trim());
        }

        WriteRaw(Environment.NewLine);
        WriteRaw(new string(IndentChar, (indentLevel - 1) * Indentation));
    }
}

Вы можете использовать его следующим образом:

[TestMethod]
public void WriteIndentedText()
{
    var result = new StringBuilder();
    using (var writer = new IndentTextXmlWriter(new StringWriter(result)){Formatting = Formatting.Indented, IndentText = true})
    {
        string text = @" Line 1
Line 2
    Line 3  ";
        // some root
        writer.WriteStartDocument();
        writer.WriteStartElement("root");
        writer.WriteStartElement("child");

        // test auto-indenting
        writer.WriteStartElement("elementIndented");
        writer.WriteString(text);
        writer.WriteEndElement();

        // test space preserving
        writer.WriteStartElement("elementPreserved");
        writer.WriteAttributeString("xml", "space", null, "preserve");
        writer.WriteString(text);

        writer.WriteEndDocument();
    }

    Debug.WriteLine(result.ToString());
}

И вывод:

<?xml version="1.0" encoding="utf-16"?>
<root>
  <child>
    <elementIndented>
      Line 1
      Line 2
      Line 3
    </elementIndented>
    <elementPreserved xml:space="preserve"> Line 1
Line 2
    Line 3  </elementPreserved>
  </child>
</root>