WPF

class MyObject {
    public string Value { get; set; }
}

<Button Content="{my:CustomBinding Value}">

public MainWindow()
{
	InitializeComponent();
	this.DataContext = MyObject;
}

<Rectangle Fill="{TemplateBinding Foreground}"
Height="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Width}"
Width="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Value}"
Margin="0,0" ></Rectangle>

public static readonly DependencyProperty RatingValueProperty =
            DependencyProperty.Register("RatingValue", typeof(int), typeof(RatingControl),
            new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(RatingValueChanged)));

public int RatingValue
        {
            get { return (int)GetValue(RatingValueProperty); }
            set
            {               
                SetValue(RatingValueProperty, value);                
            }
        }

private static void RatingValueChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
         //... change the rating value
        }