What's Wrong With This Code (#5)

Tuesday, September 12, 2006

Joe Developer is working on a bowling program (again). Joe wrote the following code.

using System;
using System.Collections.Generic;

[Serializable]
class Bowlers
{
    List<string> _bowlerList = new List<string>();

    public void AddBowler(string name)
    {
        _bowlerList.Add(name);

        EventHandler<BowlerAddedEventArgs> handler = BowlerAdded;
        if (handler != null)
        {
            handler(this, new BowlerAddedEventArgs(name));
        }
    }

    public event EventHandler<BowlerAddedEventArgs> BowlerAdded;

    // ...
}

[Serializable]
class BowlerAddedEventArgs : EventArgs
{
    public BowlerAddedEventArgs(string name)
    {
        Name = name;
    }

    public string Name;
} 

Joe unit tested the code to within an inch of its life, so he was surprised when another developer wrote the following program, which throws an exception.

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

class Test
{
    public static void Main()
    {
        Bowlers bowlers = new Bowlers();

        string addedMessage = "Added bowler: {0}";
        bowlers.BowlerAdded +=
            delegate(object sender, BowlerAddedEventArgs e)
            {
                Console.WriteLine(addedMessage, e.Name);
            };

        bowlers.AddBowler("Bob");
        bowlers.AddBowler("Jan");
        bowlers.AddBowler("Ann");

        using (MemoryStream stream = new MemoryStream())
        {
            BinaryFormatter formatter = new BinaryFormatter();
            formatter.Serialize(stream, bowlers);
        }
    }
}   

What's wrong?

Hint: the exception is a strange looking serialization exception.

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