How to implement INotifyPropertyChanged for derived classes?

Question

I have a base class:

public class PersonBaseClass : INotifyPropertyChanged
{
    private string name;
    public string Name
    {
        get { return name; }
        set
        {
            if (value != name)
            {
                name = value;
                NotifyPropertyChanged("Name");
            }
        }
    }
}

and a derived class

public class TeacherClass : PersonBaseClass, INotifyPropertyChanged
{
    private string id;
    public string Id
    {
        get { return id; }
        set
        {
            if (value != id)
            {
                id = value;
                NotifyPropertyChanged("Id");
            }
        }
    }
}

and this magic code at the end of each one above!

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

Then I show a list of Teachers collection in a list in xaml. Now if I change Id, changes will appear for user, but changes in Name which is a property in base class doesn't appear. In debug, I see after setting Name value, the handler inside NotifyPropertyChanged method is null which seems it is the problem.

How can I solve it to changes of base class also appear in the list?

Answer 1

Have only PersonBaseClass implementing INotifyPropertyChanged and make NotifyPropertyChange as protected so you can call it from child classes. There is not need to implement it twice. That should fix the problem as well.

Answer 2

Your "magic code" section should only be in PersonBaseClass. You can make the NotifyPropertyChanged function protected so that the same function can be called from TeacherClass as well.