I don't know why my class cannot be serialized

Question

I completed coding my application. But when I click start button, my app raised a exceptions.. :'(

A first chance exception of type 'System.Runtime.Serialization.InvalidDataContractException' occurred in System.Runtime.Serialization.dll
A first chance exception of type 'System.Reflection.TargetInvocationException' occurred in mscorlib.dll
A first chance exception of type 'System.Runtime.Serialization.InvalidDataContractException' occurred in System.Runtime.Serialization.dll

So I saw argument e of 'Application_UnhandledException', and I could know the reason. "'Type 'GPACalculator.Subject' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute."

I just make my class using default data types..

public class Subject : INotifyPropertyChanged
{
    private string name;
    private GradePoint gradePoint;
    private int credit;

    public Subject(string name)
    {
        Name = name;
        GradePoint = new GradePoint();
    }

    public string Name
    {
        get { return name; }
        set
        {
            Debug.WriteLine("Name: " + value);
            if (name != value)
            {
                name = value;
                OnPropertyChanged("Name");
            }
        }

    }

    public GradePoint GradePoint
    {
        get { return gradePoint; }
        set
        {
            if (gradePoint != value)
            {
                gradePoint = value;
                OnPropertyChanged("GradePoint");
            }
        }
    }

    public int Credit
    {
        get { return credit; }
        set
        {
            if (credit != value)
            {
                credit = value;
                OnPropertyChanged("Credit");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}


public class GradePoint : INotifyPropertyChanged
{
    private string mainGradePoint;
    private string subGradePoint;
    private int credit;

    public int Credit
    {
        get { return credit; }
        set
        {
            if (credit != value)
            {
                credit = value;
                OnPropertyChanged("Credit");
            }
        }
    }

    public string MainGradePoint
    {
        get { return mainGradePoint; }
        set
        {
            value = value.ToUpper();
            if (mainGradePoint != value)
            {
                mainGradePoint = value;
                OnPropertyChanged("MainGradePoint");
            }
        }
    }

    public string SubGradePoint
    {
        get { return subGradePoint; }
        set
        {
            if (subGradePoint != value)
            {
                subGradePoint = value;
                OnPropertyChanged("SubGradePoint");
            }
        }
    }

    public override string ToString()
    {
        return string.Format("{0}{1}", mainGradePoint, subGradePoint);
    }

    public double ToDouble(double perfectScore = 4.5F)
    {
        double gap = perfectScore - Math.Floor(perfectScore);
        double value;


        switch (mainGradePoint)
        {
            case "A":
                value = 4.0;
                break;
            case "B":
                value = 3.0;
                break;
            case "C":
                value = 2.0;
                break;
            case "D":
                value = 1.0;
                break;
            default:
                value = 0.0;
                return value;
        }

        switch (subGradePoint)
        {
            case "+":
                value += gap;
                break;
            case "-":
                value -= gap;
                break;
        }

        return value;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

The above is my class..

please help me

Answer 1

Start by decorating your classes with the appropriate attributes for the serializer you want to use, e.g. [Serializable] for BinaryFormatter, or [DataContract] for contract based formatters.

Note: If you use the [Serializable] attribute, remember to mark the event fields with [field:NonSerialized] otherwise all the listeners of those events will be serialized as well.