Why is BinaryFormatter trying to serialize an Event on a Serializable class?

Question

I have a simple class that is marked as Serializable, and it happens to have an event. I tried to mark the event member as NonSerialized, however the compiler complains. Yet when I go to serialize the class instance, the BinaryFormatter throws an exception that the event is non serializable. Does that mean you can't serialize classes that have events? If so, then the compiler should say so up front.

Stream file = File.Open("f", FileMode.Open);
BinaryFormatter bf = new BinaryFormatter();

object obj = null;
try
{
    obj = bf.Deserialize(file);
}
catch (System.Runtime.Serialization.SerializationException e)
{
    MessageBox.Show("De-Serialization failed : {0}", e.Message);
}
file.Close();

System.Collections.ArrayList nodeList = obj as System.Collections.ArrayList;

foreach (TreeNode node in nodeList)
{
    treeView.Nodes.Add(node);
}

Fails to work on the following class:

[Serializable()]
class Simple
{
    private int myInt;
    private string myString;
    public event SomeOtherEventDefinedElsewhere TheEvent;

}

Can you explain a little more about what you are trying to do and possibly give us a little code snippet? — IAbstract
Sure. I just have this class that has mostly string and int properties. But it has a few events to notify consumers when the instances of it change. I am storing instances of this class in the Tag property of a .NET TreeView class, or more specifically, in each Tag property of each TreeNode that corresponds to the object. When I try to serialize the TreeView to disk (storing each node in an ArrayList and then writing out the list), I get an exception: "Type 'MyEventSubscriber' in Assembly 'MyAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable." — Rhubarb
cont... MyEventSubscriber happens to be the class instance of the subscriber to the event on the class I'm trying to serialize (the one that is in the Tag property of the TreeNode). — Rhubarb
Please edit the original question (then you can use formating) also, we really need to see some code, please make a simple case that shows the problem. — Hogan
"I tried to mark the event member as NonSerialized, however the compiler complains". What error do you get? — Foole

Asad Asad · Accepted Answer · 2010-02-22T03:30:59

"In the case of events, you must also add the field attribute qualifier when applying the NonSerialized attribute so that the attribute is applied to the underlying delegate rather than to the event itself" Advanced Serialization - MSDN

Prefix the NonSerializedAttribute with field

[field:NonSerialized]
public event MyEventHandler MyEvent;

Why is BinaryFormatter trying to serialize an Event on a Serializable class?

3 Answers