How does XML Serialization know where to put the attribute?

Question

I am trying to figure out how to do XML serialization.

This is how I want my XML document too look like in the end

<course>
    <name></name>
    <backgroundColor></backgroundColor>
    <fontColor></fontColor>
    <sharingKey></sharingKey>
    <task id="">
        <taskName></taskName>
        <description></description>
    </task>
    <task id="">
        <taskName></taskName>
        <description></description>
    </task>
</course>

So far mine looks like

<?xml version="1.0" encoding="utf-8"?>
<Course xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <name>name</name>
  <backgroundColor>test</backgroundColor>
  <fontColor>test2</fontColor>
  <sharingKey>9324bfab-6cc7-49e5-84f7-56130b8dc099</sharingKey>
  <task id="first Task" />
  <task id="Second task" />
</Course>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;

namespace ConsoleApplication1
{
    [XmlRoot("Course")]
    public class MyWrapper 
    {
        public MyWrapper()
        {
            TaskList = new List<Tasks>();
        }

        [XmlElement("name")]
        public string Name { get; set; }

        [XmlElement("backgroundColor")]
        public string BackgroundColor { get; set; }

        [XmlElement("fontColor")]
        public string  FontColor { get; set; }

        [XmlElement("sharingKey")]
        public Guid SharingKey { get; set; }

        [XmlElement("task")]
        public List<Tasks> TaskList { get; set; }

    }


    public class Tasks
    {
        [XmlAttribute("id")]
        public string Id { get; set; }
    }

}


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            Tasks task = new Tasks();
            task.Id = "first Task";

            Tasks task2 = new Tasks();
            task2.Id = "Second task";

            MyWrapper wrap = new MyWrapper();
            wrap.BackgroundColor = "test";
            wrap.FontColor = "test2";
            wrap.Name = "name";
            wrap.SharingKey = Guid.NewGuid();

            wrap.TaskList.Add(task);
            wrap.TaskList.Add(task2);

            SerializeToXML(wrap);
        }

        static public void SerializeToXML(MyWrapper list)
        {
            XmlSerializer serializer = new XmlSerializer(typeof(MyWrapper));


       TextWriter textWriter = new StreamWriter(@"C:\New folder\test.xml");
        serializer.Serialize(textWriter, list);
        textWriter.Close();
    }
}

}

So my question is with the "id" for the task.

All I have is another class with this in it

[XmlAttribute("id")]
public string Id { get; set; }

How did it know to put this attribute in the task tag?

What happens if I wanted to have another property

[XmlElement()]
public string TaskName {get; set;}

Say I wanted to have an attribute with this element how would I make sure that the attribute would be with TaskName not with Task?

Answer 1

[XmlElement("task")]
public List<Tasks> TaskList { get; set; }

This part of your code told it to serialize every Tasks object in an element called "task". The serializer looks at the properties on the Tasks class and finds the Id property which you marked with [XmlAttribute("id")] so it gets serialized as an attribute to the "task" element for the object.

I'm not sure I understand your second question. You cannot add an attribute to the element because its type is a string. Instead you would have to create a new class to wrap the concept of a task name which would have a name property and whatever other properties you wanted to add to it.

Answer 2

Basically: XML elements can have two kinds of properties, attributes and elements. You defined an XML element task and an attribute on task called id, thus the serializer adds the attribute to task.

Now, suppose you want to add elements to reside within task -- this is also okay, as I said, XML elements can contain other elements, or have attributes. Simply define any elements you want to contain within task...within task.

If you want to have an attribute attached to a different element, you need to create a new XML element (here that corresponds to a class) and literally set it as an attribute type using the [XmlAttribute("id")] syntax.

Perhaps there's a disconnect for you here -- when you define the simplest form of element, we can call that a simpleType, and it can have values that are Strings or Integers or any kind of relatively primitive type (dates are valid, too). But if you want that same element to also have attributes, it suddenly needs to become a complexType, since it has complexContent -- it may contains both simple content, and properties, like, say, an attribute.

Take a look at how to write XML Schemas - w3schools have some excellent tutorials - I think that you'll gain a much better understanding of this whole mix of simple and complex content. Effectively, by defining an XML serialization for your classes you are also defining an XML schema; and you can in fact compile your code into such a schema. Understanding to construct the schemas will let you understand how to construct your code to generate the appropriate schemas, and additionally, understand your serialization output.