Property depending on property from another class

Question

I've got a Windows Phone 8 application using Fody to inject INotifyPropertyChanged into properties. I have Class First with property A which is binded to textbox in View:

[ImplementPropertyChanged]
public class First
{
    public int A { get; set; }

    public int AA { get {return A + 1; } }
}

And class Second with property B depending on property A (also binded to textbox):

[ImplementPropertyChanged]
public class Second
{
    private First first;

    public int B { get {return first.A + 1; } }
}

Updating A and AA works fine, however B doesn't update automatically when first.A changes. Is there an easy and clean way to achieve such automatical updates using fody or do I have to create my own event to handle it?

Answer 1

I ended up using standard INotifyPropertyChanged in the way SKall suggested.

public class First : INotifyPropertyChanged
{
    public int A { get; set; }

    public int AA { get {return A + 1; } }

    (...) // INotifyPropertyChanged implementation
}

public class Second : INotifyPropertyChanged
{
    private First first;

    public Second(First first)
    {
        this.first = first;
        this.first.PropertyChanged += (s,e) => { FirstPropertyChanged(e.PropertyName);

        public int B { get {return first.A + 1; } }

        protected virtual void FirstPropertyChanged(string propertyName)
        {
            if (propertyName == "A")
                NotifyPropertyChanged("B");
        }

        (...) // INotifyPropertyChanged implementation
    }
};