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..

Link moved again: http://george.softumus.com/inotifypropertychanged-and-magic-strings/ — CAD bloke, Apr 25 '16 at 02:35

score 6 · Accepted Answer · answered Jan 31 '12 at 09:23

6

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).

answered Jan 31 '12 at 09:23

H.B.

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1

@eMi: I said you should use the method, making it `protected` is just the necessary step to do so. Do not try to raise the event. – H.B. Jan 31 '12 at 09:27

score 3 · Answer 2 · answered Jan 31 '12 at 09:33

Change derived class as follow:

public class SchemaDifferenceViewModel : BaseViewModel
{
    private string firstSchemaToCompare;

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

score 0 · Answer 3 · answered Jan 31 '12 at 09:49

Making a base class for INPC is bad design in my opinion.

This is the textbook place where you could use a mixin

In short, it allows you to provide a default implementation of an interface's members. You would still be able to inherit from an actually interesting class =)

Inheriting from one baseclass that implements INotifyPropertyChanged?

3 Answers3