Serialization of a class with events

Question

I have a Class like this:

public delegate void ChangedEventHandler(object sender, EventArgs e);
[Serializable]
public class valueDouble
{
    public event ChangedEventHandler Changed;
    public double value
    {
        get { return _value; }
        set 
        {
            _value = value;
            if (Changed != null)
            {
                Changed(this, EventArgs.Empty);
            }
        }
    }
    private double _value = 0;
}

I also have another Class (StepPulseblaster) which is not serializable and adds an Event Handler

valDouble.Changed += new ChangedEventHandler(sc_PropertyChanged);

When i try to serialize the valueDouble Class, there will be an error:

The Type StepPulseblaster is not marked as serializable

When i comment the line

valDouble.Changed += ...

there will be no error any more.

How can i serialize a class which has some events connected?

Samothrace

Do you want the events to still be there when you deserialize it, or do you want to serialize the data without the events? – Lindholm

I use the Event to update a GUI, so i need the event after I deserialize it. I have about 1000 duplicates of this Class so I do not really want to delete the event before serialization and create it again. – Samothrace

Okay, next question: why are you serializing the object? Are you storing it somewhere and reloading it later, or are you making it accessible to a different context (e.g. a different AppDomain or a different process)? You won't be able to serialize the reference to your GUI, but depending on what you need, there may be easy ways to accomplish what you're after. – Lindholm

I want to save it to disk and be able to restore it later. – Samothrace

Answer 1

You should do:

[field: NonSerialized]
public event ChangedEventHandler Changed;

As described in the MSDN:

To apply the NonSerializedAttribute class to an event, set the attribute location to field.

Pinkie

Thats interesting, never knew you could do that. – Wagoner

That link to the docs does not seem to go anywhere useful. Has there been some link rot? – Hyunhz

Answer 2

The NonSerialized attribute is only available for fields, so to use it you have to adjust your code to use fields.

Try creating your event like this:

[NonSerialized]
private ChangedEventHandler _changed;
public event ChangedEventHandler Changed
{
    add { _changed += value; }
    remove { _changed -= value; }
}

Then in the value property use the field, not the property:

public double value
{
    get { return _value; }
    set 
    {
        _value = value;
        if (_changed != null)
        {
            _changed(this, EventArgs.Empty);
        }
    }
}
private double _value = 0;

Obedient

Answer 3

Use the [NonSerialized] attribute to avoid serialization of the event.

Spectroscope

In VS2010, applying [NonSerialized] to an event gives an error: "Error 2 Attribute 'NonSerialized' is not valid on this declaration type. It is only valid on 'field' declarations." – Greenbelt

Answer 4

Either mark StepPulseBlaster as serializable or use the XmlIgnore attribute to prevent Changed from being serialized.

Defaulter