So I decided to implement XmlSerializer “again”

Reinventing the wheel T_T

ref = CXuesong/XSerializer/

Pull is welcomed T_T if you’d like to

Recently I’ve been considering the following problems:

When serializing using `XmlSerializer` to get more control on what the XML should look like,

  1. How to serialize members with type `Nullable<T>`, persisting it as XML attribute (rather than element)?
  2. How to serialize references, avoiding it persisted as multiple identical copies of one object?
  3. How to achieve the these two things above, without introducting public auxiliary properties?
    (e.g. for case 1, an auxiliary property can be introduced to do the conversions between `Nullable<T>` and `string`, the latter of which can be persisted as XML attribute.)

It seems that case 2 can be solved using `DataContractSeriallizer`. However, `DataContractSeriallizer` generates Id by itself, and represent Id and its references with `z:Id` and`z:Ref`. As I’ve mentioned in previously (在 XmlSerializer 与 DataContractSerializer 之间抉择), `DataContractSeriallizer` is rather rigid when you want to control the appearance of XML tree it generates.

Then, how to solve these problems?

Maybe, I’ll reinvent the wheel.

See Also

c# – Is there any way for my class to support serialisation as an XML attribute? – Stack Overflow

The exapmle provided in section “Serializing Derived Classes”(with XmlArrayItemAttribute) may be not the case

cite=https://msdn.microsoft.com/EN-US/library/vstudio/2baksw0z.aspx

Another use of the XmlArrayItemAttribute is to allow the serialization of derived classes. For example, another class named Manager that derives from Employee can be added to the previous example. If you do not apply the XmlArrayItemAttribute, the code will fail at run time because the derived class type will not be recognized. To remedy this, apply the attribute twice, each time setting the Type property for each acceptable type (base and derived).

public class Group{
    [XmlArrayItem(Type = typeof(Employee)),
    XmlArrayItem(Type = typeof(Manager))]
    public Employee[] Employees;
}
public class Employee{
    public string Name;
}
public class Manager:Employee{
    public int Level;
}

A serialized instance might resemble the following.

<Group>
<Employees>
    <Employee>
        <Name>Haley</Name>
    </Employee>
    <Employee xsi:type = "Manager">
        <Name>Ann</Name>
        <Level>3</Level>
    <Employee>
</Employees>
</Group>

However, this is not the case.
I used the following test case:

using System;
using System.IO;
using System.Xml.Serialization;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            var f = new XmlSerializer(typeof (Group));
            using (var sw = new StringWriter())
            {
                f.Serialize(sw, new Group()
                {
                    Employees =
                    new [] {
                        new Employee {Name = "Jerry"},
                        new Manager {Name = "Tom", Level = 20}
                    }
                });
                Console.WriteLine(sw.ToString());
            }
        }
    }

    public class Group
    {
        [XmlArrayItem(Type = typeof (Employee)),
         XmlArrayItem(Type = typeof (Manager))] public Employee[] Employees;
    }

    public class Employee
    {
        public string Name;
    }

    public class Manager : Employee
    {
        public int Level;
    }
}

which yields the result:

<?xml version="1.0" encoding="utf-16"?>
<Group xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Employees>
    <Employee>
      <Name>Jerry</Name>
    </Employee>
    <Manager>
      <Name>Tom</Name>
      <Level>20</Level>
    </Manager>
  </Employees>
</Group>

As you can see, `xsi:type` attribute didn’t appeared in the XML document containing the serialized `Group` instance. Instead, the element name of derived `Manager` class is employed.
If I modify the definition of `Group` class to

    [XmlInclude(typeof(Manager))]
    public class Group
    {
        [XmlArrayItem(Type = typeof (Employee))] public Employee[] Employees;
    }

Then I get the following result

<?xml version="1.0" encoding="utf-16"?>
<Group xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Employees>
    <Employee>
      <Name>Jerry</Name>
    </Employee>
    <Employee xsi:type="Manager">
      <Name>Tom</Name>
      <Level>20</Level>
    </Employee>
  </Employees>
</Group>

which coincides with the example output stated on MSDN.
p.s. I tested the code above in VS 2013.

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