How to make an XML tag mandatory with a self-closing tag, using the serialiser?-CodePudding

I'm working on a C# program and I'm trying to serialise XML.

I have the following tag:

using System.Xml.Serialization;
...
[XmlElement("MV")]
public MultiVerse MultiVerse { get; set; }

When I don't fill in this value, the tag <MV> is not present, but I would like to get a tag <MV/> in that case:

Currently I have <HM><ID>Some_ID</ID></HM>.
I'd like to have <HM><ID>Some_ID</ID><MV/></HM>.

I already tried preceeding the line with [Required] but that didn't work, and I think that filling in the IsNullable attribute is the good approach.

Edit1, after some investigation on the internet
On the internet, there are quite some advises on modifying the XmlWriter but in my project, the whole serialisation is done as follows:

public override string ToString()
{
    ...
    using (var stream = new StringWriter())
    using (var writer = XmlWriter.Create(stream, settings))
    {
        var serializer = new XmlSerializer(base.GetType());
        serializer.Serialize(writer, this, ns);
        return stream.ToString();
    }
    ...
}

As you can see, this is so general that I prefer not to do any modifications in here, hence I'm looking for a way to customise the [XmlElement] directive.

Edit2: XmlWriter settings:
The XmlWriter settings look as follows:

// Remove Declaration
var settings = new XmlWriterSettings
{
    Indent = false,
    OmitXmlDeclaration = true,
    NewLineHandling = NewLineHandling.None,
    NewLineOnAttributes = false,
};

Does anybody have an idea?

Thanks in advance

CodePudding user response：

There is https://docs.microsoft.com/en-us/dotnet/api/system.xml.serialization.xmlelementattribute.isnullable?view=net-6.0 so e.g.

[XmlElement("MV", IsNullable=true)]
public MultiVerse MultiVerse { get; set; }

would give you, for a null value, a serialization as <MV xsi:nil="true" /> (or possibly <MV xsi:nil="true"></MV> as ensuring the short tag notation is not something the standard writers give you control over but my experience is that .NET usually uses it for empty elements so you might be lucky that your wanted serialization format is the default one .NET outputs).

CodePudding user response：

This is the way I'm currently solving my issue (don't laugh):

public override string ToString()
{
    string temp = base.ToString();
    temp = temp.Replace(" p2:nil=\"true\"", "");
    temp = temp.Replace(" xmlns:p2=\"http://www.w3.org/2001/XMLSchema-instance\"", "");
    temp = temp.Replace("MV />", "MV/>");
    return temp;
}

This is hidious! Does anybody have a better solution?

Thanks