Sample.cs

public class Machine : INotifyPropertyChanged
{
    private Tool _tool;
    
    public event PropertyChangedEventHandler PropertyChanged;
    
    public event EventHandler<ToolChangedEventArgs> ToolChanged;

    public Tool Tool
    {
        get { return _tool; }
        set
        {
            if (Equals(value, _tool))
            {
                return;
            }
            _tool = value;
            OnPropertyChanged();
        }
    }
    protected virtual void OnToolChanged(ToolChangedEventArgs e)
    {
        var handler = ToolChanged;
        if (handler != null)
        {
            handler(this, e);
        }
    }

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}