using System;

using System.ComponentModel;

using System.Runtime.CompilerServices;

​

Someclass a = new Someclass();

BikeStore b = new BikeStore(a);

Shopper c = new Shopper(a);

​

a.SelectedItem = default;

​

public class Someclass : INotifyPropertyChanged

{

    private static object _selectedItem;

​

    public object SelectedItem

    {

        get => _selectedItem ?? new object();

        set

        {

            _selectedItem = value;

            OnPropertyChange(nameof(SelectedItem)); 

        }

    }

​

    private void OnPropertyChange([CallerMemberName] string propertyName = null)

    {

        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

    }

​

    public event PropertyChangedEventHandler PropertyChanged;

}

​

public class BikeStore

{

    public BikeStore(Someclass someClass)

    {

        someClass.PropertyChanged += BikeStore_PropertyChanged;

    }

​

    private void BikeStore_PropertyChanged(object sender, PropertyChangedEventArgs e)

    {

        Console.WriteLine(nameof(BikeStore_PropertyChanged));

    }

}

​

public class Shopper

{

    public Shopper(Someclass someClass)

    {

        someClass.PropertyChanged += Shopper_PropertyChanged;

    }

​

    private void Shopper_PropertyChanged(object sender, PropertyChangedEventArgs e)

    {

        Console.WriteLine(nameof(Shopper_PropertyChanged));

    }

}