Serialize a custom generic type implementing IEnumerable in c#

Question

I have a generic type Foo1 which is basically a container with some metadata and a generic list. When I serialize that type, it gets the name "Foo1Of" + TypeParameterName.

public class Foo1<T>
{
    public string Name { get; set; } = string.Empty;

    public List<T> List { get; set; } = new List<T>();
}

[TestMethod]
public void SerializeFoo1()
{
    Foo1<string> foo = new Foo1<string>
    {
        Name = "Foo1",
        List =
        {
            "Bar",
            "Baz"
        }
    };

    XmlSerializer s = new XmlSerializer(foo.GetType());
    StringBuilder sb = new StringBuilder();
    XmlWriter w = XmlWriter.Create(sb);

    s.Serialize(w, foo);

    Console.WriteLine(sb.ToString());
}

This is the old version and returns:

<?xml version="1.0" encoding="utf-16"?>
<Foo1OfString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Name>Foo1</Name>
    <List><string>Bar</string><string>Baz</string></List>
</Foo1OfString>

To access the internal list more directly I implemented IEnumerable, IEnumerable and an Add(...) method.

public class Foo2<T> : IEnumerable<T>, IEnumerable
{
    public string Name { get; set; } = string.Empty;

    public List<T> List { get; set; } = new List<T>();

    public void Add(T item)
    {
        List.Add(item);
    }

    public IEnumerator<T> GetEnumerator()
    {
        return List.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return List.GetEnumerator();
    }
}

[TestMethod]
public void SerializeFoo2()
{
    Foo2<string> foo = new Foo2<string>
    {
        Name = "Foo2",
        List =
        {
            "Bar",
            "Baz"
        }
    };

    XmlSerializer s = new XmlSerializer(foo.GetType());
    StringBuilder sb = new StringBuilder();
    XmlWriter w = XmlWriter.Create(sb);

    s.Serialize(w, foo);

    Console.WriteLine(sb.ToString());
}

After doing that, XML Serialization behaves very strange:

<?xml version="1.0" encoding="utf-16"?>
<ArrayOfString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <string>Bar</string><string>Baz</string>
</ArrayOfString>

The name becomes "ArrayOf" + TypeParameterName and the property "Name" vanishes. The XmlSerializer seems to think, that my custom type is an array. Is there a way to change this behaviour which means to be able to implement the interfaces and Add(...) but get the old XML serialization?

Answer 1

This is default behavior of XmlSerializer as you are implementing IEnumerable<T> interface. Due to IEnumerable<string> type, XmlSerializer thinks it is a collection/array of string.

If you must implemented IEnumerable<T>, then one way to overcome this default behavior is to implement custom serialization. Implement IXmlSerializable for your Foo1<T>. You can then customize the Xml graph as you wish, and return your desired Name and List. XmlSerializer will then your custom implementation.