silverlight属性改变事件通知

工作中遇到silverlight本身没有提供的某些属性改变事件，但又需要在属性改变时得到通知，Google搬运stack overflow，原地址

 /// Listen for change of the dependency property
    public void RegisterForNotification(string propertyName, FrameworkElement element, PropertyChangedCallback callback)
    {

        //Bind to a depedency property
        Binding b = new Binding(propertyName) { Source = element };
        var prop = System.Windows.DependencyProperty.RegisterAttached(
            "ListenAttached"+propertyName,
            typeof(object),
            typeof(UserControl),
            new System.Windows.PropertyMetadata(callback));

        element.SetBinding(prop, b);
    }

RegisterForNotification("Text", this.txtMain,(d,e)=>MessageBox.Show("Text changed"));
RegisterForNotification("Value", this.sliderMain, (d, e) => MessageBox.Show("Value changed"));

 更正：以上方法可能会造成回调方法callback内存泄漏，改为封装一个方法再调用callback

        /// <summary>
        /// 监听任意依赖属性值改变事件的辅助方法
        /// </summary>
        /// <param name="element"></param>
        /// <param name="propertyName"></param>
        /// <param name="callback"></param>
        public static void ListenForChange(FrameworkElement element, string propertyName, PropertyChangedCallback callback)
        {
            var b = new Binding(propertyName) { Source = element };
            var prop = DependencyProperty.RegisterAttached("ListenAttached" + propertyName, typeof(object), typeof(FrameworkElement), new PropertyMetadata(new WeakPropertyChangedCallback(callback).PropertyChangedCallback));
            element.SetBinding(prop, b);
        }

        /// <summary>
        /// 解决ListenForChange导致的内存泄漏：
        /// 避免DependencyProperty.RegisterAttached中元数据对PropertyChangedCallback的引用导致的内存泄漏
        /// 但会导致WeakPropertyChangedCallback对象本身的泄漏，WeakPropertyChangedCallback对象本身不大，可以忽略
        /// 即：以WeakPropertyChangedCallback对象的内存泄漏（很小） >>>===>>> 替代PropertyChangedCallback所在对象的内存泄漏（可能很大）
        /// 
        /// TODO:暂时未找到其他的方式, DependencyProperty.RegisterAttached、PropertyMetadata缺少相关的清除方法
        /// silverlight缺少BindingOperations.ClearBinding方法
        /// </summary>
        class WeakPropertyChangedCallback
        {
            private WeakReference callback;
            public WeakPropertyChangedCallback(PropertyChangedCallback callback)
            {

                this.callback = new WeakReference(callback);
            }

            /// <summary>
            /// 转发到callback
            /// </summary>
            /// <param name="d"></param>
            /// <param name="e"></param>
            public void PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
            {
                if (callback.IsAlive)
                {
                    var cb = callback.Target as PropertyChangedCallback;
                    if (cb != null)
                        cb(d, e);
                }
            }
        }