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
代码语言：javascript复制 /// 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
代码语言：javascript复制 /// <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);
}
}
}
