silverlight属性改变事件通知

• 2019 年 10 月 10 日
• 笔记

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);                  }              }          }