wp8和wpf里监听控件自带属性的变化

在wpf里，有DependencyPropertyDescriptor类可以轻松实现监听控件自带属性的变化，如下：

 DependencyPropertyDescriptor dpd = DependencyPropertyDescriptor.FromProperty(TextBlock.FontSizeProperty, typeof(TextBlock));
 if (dpd != null)
 {
     dpd.AddValueChanged(textBlockTitle, OnFontSizeChanged);
 }

但是wp8里没有这个类，我们使用DependencyProperty.RegisterAttached来间接实现：

 public static void RegisterForNotification(string propertyName, FrameworkElement element, PropertyChangedCallback callback)
 {
     //Bind to a depedency property
     Binding bind = new Binding(propertyName) { Source = element };
     DependencyProperty dp = System.Windows.DependencyProperty.RegisterAttached(
         "ListenAttached" + propertyName,
         typeof(object),
         typeof(UserControl),
         new System.Windows.PropertyMetadata(callback));
     element.SetBinding(dp, bind);
 }