DepedencyProperty_MultiplyByTwo.cs

public class MultiplyByTwo : DependencyObject
{
    private static readonly DependencyPropertyKey ResultPropertyKey =
        DependencyProperty.RegisterReadOnly(nameof(Result), typeof(int), typeof(MultiplyByTwo),
            new PropertyMetadata(0));

    public static readonly DependencyProperty NumberProperty =
        DependencyProperty.Register(nameof(Number), typeof(int), typeof(MultiplyByTwo),
            new PropertyMetadata(0, CalculateResult));

    public static readonly DependencyProperty ResultProperty = ResultPropertyKey.DependencyProperty;


    public int Number
    {
        get { return (int)GetValue(NumberProperty); }
        set { SetValue(NumberProperty, value); }
    }

    public int Result
    {
        get { return (int)GetValue(ResultProperty); }
    }


    private static void CalculateResult(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        d.SetValue(ResultPropertyKey, (int)e.NewValue * 2);
    }
}