How to use XmlInclude to serialize IEnumerable

Question

I've run into an issue with serializing an IEnumerable with the XmlSerializer . Since IEnumerable represents a list of object , XmlSerializer doesn't know ahead of time what types it needs to serialize. But because it needs to know, it throws an InvalidOperationException when it encounters a type other than object .

The type Foo.Bar was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.

The XmlIncludeAttribute is intended to be applied to a method to indicate that the return value can be a certain type. However, IEnumerable has no method that I could put the attribute on.

I tried applying them to GetEnumerator :

public class Bar : IEnumerable
{
    private List<object> list;

    public Bar()
    {
    }

    [XmlInclude(typeof(Bar))]
    [XmlInclude(typeof(ChildBar))]
    public IEnumerator GetEnumerator()
    {
        return list.GetEnumerator();
    }

    public void Add(Bar bar)
    {
        list.Add(bar);
    }

    public void Add(ChildBar childBar)
    {
        list.Add(childBar);
    }

    // used for deserialization
    public void Add(object o)
    {
        if (o is Bar || o is ChildBar)
        {
            list.Add(o);
        }
    }

    // more irrelevant stuff
}

public class ChildBar
{
    public ChildBar()
    {
    }

    // more irrelevant stuff
}

That didn't solve it, and I have no idea where else to use the attributes.

Where should I put them? Can I work around it without them? Can I avoid writing my own enumerator?

Answer 1

EDIT: Since their were a couple flaws with my previous answer -didn't have bar containing more bars and didn't use xmlAttributes here is my new solution: This does not implement however...

EDIT: Well I've gone back and reviewed some things and this is my final solution by implementing ICollection, hope this helps anyone trying to find a solution to serializing Collections.

public class Program
{
    static void Main(string[] args)
    {
        var program = new Program();

        program.SerializeObject();
    }

    private int tierIndex = 1;

    public void SerializeObject()
    {
        var barCollection = new BarCollection();
            var bar1 = new Bar() { Name = "bar1" };
            barCollection.Add(bar1);
            var bar2 = new Bar() { Name = "bar2" };
            barCollection.Add(bar2);
                var bar3 = new Bar() { Name = "bar3" };
                bar2.BarCollection.Add(bar3);
                var bar4 = new Bar() { Name = "bar4" };
                bar2.BarCollection.Add(bar4);
            var bar5 = new Bar() { Name = "bar 5" };
            barCollection.Add(bar5);
            var bar6 = new Bar() { Name = "bar 6" };
            barCollection.Add(bar6);
                var bar7 = new Bar() { Name = "bar 7" };
                bar6.BarCollection.Add(bar7);
                    var bar8 = new Bar() { Name = "bar 8" };
                    bar7.BarCollection.Add(bar8);



        var x = new XmlSerializer(typeof(BarCollection));
        x.Serialize(Console.Out, barCollection);

        Console.WriteLine("\n");

        WriteCollection(barCollection);

        Console.ReadLine();
    }

    public void WriteCollection(BarCollection barCollection)
    {
        tierIndex++;

        foreach (Bar bar in barCollection)
        {
            Console.Write(new StringBuilder().Insert(0, "--", tierIndex) + "> ");
            Console.Write(bar.Name + "\n");

            WriteCollection(bar.BarCollection);
        }

        tierIndex--;
    }
}

public class BarCollection : ICollection
{
    private readonly ArrayList barNodes = new ArrayList();

    public Bar this[int index]
    {
        get { return (Bar) barNodes[index]; }
    }

    public void CopyTo(Array a, int index)
    {
        barNodes.CopyTo(a, index);
    }

    public int Count
    {
        get { return barNodes.Count; }
    }

    public object SyncRoot
    {
        get { return this; }
    }

    public bool IsSynchronized
    {
        get { return false; }
    }

    public IEnumerator GetEnumerator()
    {
        return barNodes.GetEnumerator();
    }

    public void Add(Bar bar)
    {
        barNodes.Add(bar);
    }

    public void Add(Object bar)
    {
        barNodes.Add((Bar) bar);
    }
}

public class Bar
{
    [XmlAttribute(AttributeName = "Name")]
    public string Name;

    [XmlArray(ElementName = "BarNodes", IsNullable = true)]
    public BarCollection BarCollection = new BarCollection();
}

Heres the output:

<?xml version="1.0" encoding="IBM437"?>
<ArrayOfBar xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <Bar Name="bar1">
    <BarNodes />
  </Bar>

  <Bar Name="bar2">
    <BarNodes>
      <Bar Name="bar3">
        <BarNodes />
      </Bar>

      <Bar Name="bar4">
        <BarNodes />
      </Bar>

    </BarNodes>
  </Bar>

  <Bar Name="bar 5">
    <BarNodes />
  </Bar>

  <Bar Name="bar 6">
    <BarNodes>
      <Bar Name="bar 7">
        <BarNodes>
          <Bar Name="bar 8">
            <BarNodes />
          </Bar>

        </BarNodes>
      </Bar>

    </BarNodes>
  </Bar>

</ArrayOfBar>

----> bar1
----> bar2
------> bar3
------> bar4
----> bar 5
----> bar 6
------> bar 7
--------> bar 8

Another Stack Reference: XmlSerializer won't serialize IEnumerable