How to implement INotifyPropertyChanged with nameof rather than magic strings?

Question

I was reading about the new nameof keyword in C# 6. I want to know how can I implement INotifyPropertyChanged using this keyword, what are the prerequisites (of course other than C# 6) and how it will effect the performance of my MVVM application?

Answer 1

It would look like this:

public string Foo
{
   get
   {
      return this.foo;
   }
   set
   {
       if (value != this.foo)
       {
          this.foo = value;
          OnPropertyChanged(nameof(Foo));
       }
   }
}

The nameof(Foo) will be substituted with the "Foo" string at compile time, so it should be very performant. This is not reflection.

Answer 2

Here's a complete code sample of a class using the new C# 6.0 sugar:

public class ServerViewModel : INotifyPropertyChanged {
    private string _server;
    public string Server {
        get { return _server; }
        set {
            _server = value;
            OnPropertyChanged(nameof(Server));
        }
    }

    private int _port;
    public int Port {
        get { return _port; }
        set {
            _port = value;
            OnPropertyChanged(nameof(Port));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName) => 
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

With this, you get the nameof() operator, the null-conditional operator ?., and an expression-bodied function (the OnPropertyChanged definition).

Answer 3

It's just a matter of using nameof() instead of the magic string. The example below is from my blog article on the subject:

private string currentTime;

public string CurrentTime
{
    get
    {
        return this.currentTime;
    }
    set
    {
        this.currentTime = value;
        this.OnPropertyChanged(nameof(CurrentTime));
    }
}

Since it is evaluated at compile-time, it is more performant than any of the current alternatives (which are also mentioned in the blog article).