Question

我想创建一个可附加的Panel事件，在调用Panel.OnVisualChildrenChanged时触发：

public class PanelObserver {
    public static readonly RoutedEvent VisualChildrenChangedEvent;

    static PanelObserver( ) {
        VisualChildrenChangedEvent = EventManager.RegisterRoutedEvent(
            "VisualChildrenChanged",
            RoutingStrategy.Bubble,
            typeof( RoutedEventHandler ),
            typeof( Panel ) );
    }

    public static void AddVisualChildrenChangedHandler(
        DependencyObject d, RoutedEventHandler handler ) {
        //Something needs to be done to d so that when OnVisualChildrenChanged is called,
        //it will fire handler.
        ( d as Panel )?.AddHandler( VisualChildrenChangedEvent, handler );
    }

    public static void RemoveVisualChildrenChangedHandler(
        DependencyObject d, RoutedEventHandler handler ) {
        //Something will likely need to be done to d here as well...
        ( d as Panel )?.RemoveHandler( VisualChildrenChangedEvent, handler );
    }
}

用例非常简单

<Grid myns:PanelObserver.VisualChildrenChanged = "SomeEventHandler" />

理想情况下，每次调用Panel.OnVisualChildrenChanged时都会引发事件。如果有可能，我需要在AddVisualChildrenChanged方法（以及它的对映体）中添加什么来实现这一目标？如果这不是如何实现这一点，那么实现这一目标的正确方法是什么？

Answer 1

我无法想出通过可附加的Panel事件触发Panel.OnVisualChildrenChanged的方法。相反，您可以从任何Panel类派生并覆盖OnVisualChildrenChanged，然后声明另一个事件。

例如：

public class ObservablePanel : Panel
{
    protected override void OnVisualChildrenChanged(DependencyObject visualAdded, DependencyObject visualRemoved)
    {
        base.OnVisualChildrenChanged(visualAdded, visualRemoved);
        VisualChildrenChanged?.Invoke(this, EventArgs.Empty);
    }
    public event EventHandler VisualChildrenChanged;
}

您无法通过可附加的面板活动进行此操作的原因：
1. Panel.Children属性是UIElementCollection，如果事件发生变化，则不会公开任何事件。＃34;。
2. Panel.Children属性是只读的，因此您无法将其设置为UIElementCollection的自定义派生实现，该实现将公开＆＃34;已更改＆＃34;事件。
3. Panel.OnVisualChildrenChanged为protected，因此您只能在Panel派生类上访问它。

如何引发附加的事件处理程序？

1 个答案: