Inheriting from one baseclass that implements INotifyPropertyChanged?

Question

I have this BaseClass:

public class BaseViewModel : INotifyPropertyChanged
{
    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

and a other class:

public class SchemaDifferenceViewModel : BaseViewModel
{
    private string firstSchemaToCompare;

    public string FirstSchemaToCompare
    {
        get { return firstSchemaToCompare; }
        set
        {
            firstSchemaToCompare = value;
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs("FirstSchemaToCompare"));
                //StartCommand.RaiseCanExecuteChanged();
            }
        }
    }

PropertyChanged is here ( 2Times ), red underlined, it says:

Error   1   The event BaseViewModel.PropertyChanged' can only appear on the left hand side of += or -= (except when used from within the type 'SchemaDifferenceFinder.ViewModel.BaseViewModel')

What I'm doing wrong? I only swept the PropertyChangedEvent to a new class: BaseViewModel..

Answer 1

You cannot raise the event outside the class it is declared in, use the method in the base class to raise it (make OnPropertyChanged protected).

Answer 2

Change derived class as follow:

public class SchemaDifferenceViewModel : BaseViewModel
{
    private string firstSchemaToCompare;

    public string FirstSchemaToCompare
    {
        get { return firstSchemaToCompare; }
        set
        {
            firstSchemaToCompare = value;
            OnPropertyChanged("FirstSchemaToCompare");
        }
    }