public class Sale : INotifyPropertyChanged
{
    private string _product;
    private double _value;
    private double _discount;
 
    public Sale(string product, double value, double discount)
    {
        Product = product;
        Value = value;
        Discount = discount;
    }
 
    public string Product
    {
        get { return _product; }
        set
        {
            if (_product != value)
            {
                _product = value;
                OnPropertyChanged("Product");
            }
        }
    }
 
    public double Value
    {
        get { return _value; }
        set
        {
            if (_value != value)
            {
                _value = value;
                OnPropertyChanged("Value");
            }
        }
    }
 
    public double Discount
    {
        get { return _discount; }
        set
        {
            if (_discount != value)
            {
                _discount = value;
                OnPropertyChanged("Discount");
            }
        }
    }
 
    public event PropertyChangedEventHandler PropertyChanged;
 
    void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}