Question

是否可以使用WeakEventManager在静态事件上创建弱事件侦听器？

我想在静态CompositionTarget.Rendering事件上创建一个弱事件侦听器，以避免在我不知道WPF / Silverlight源元素的生命周期时发生内存泄漏。

我通过weak event pattern实现了渲染事件管理器：

public class RenderingEventManager : WeakEventManager
{
    public static void AddListener(IWeakEventListener listener)
    {
        CurrentManager.ProtectedAddListener(null, listener);
    }

    public static void RemoveListener(IWeakEventListener listener)
    {
        CurrentManager.ProtectedRemoveListener(null, listener);
    }

    private static RenderingEventManager CurrentManager
    {
        get
        {
            var managerType = typeof(RenderingEventManager);
            var manager = (RenderingEventManager)GetCurrentManager(managerType);
            if (manager == null)
            {
                manager = new RenderingEventManager();
                SetCurrentManager(managerType, manager);
            }
            return manager;
        }
    }

    protected sealed override void StartListening(object source)
    {
        CompositionTarget.Rendering += this.OnCompositionTargetRendering;
    }

    protected sealed override void StopListening(object source)
    {
        CompositionTarget.Rendering -= this.OnCompositionTargetRendering;
    }

    void OnCompositionTargetRendering(object sender, EventArgs e)
    {
        this.DeliverEvent(sender, e);
    }
}

并在一个简单的窗口中测试了经理：

public partial class Window1 : Window, IWeakEventListener
{
    public Window1()
    {
        InitializeComponent();
        RenderingEventManager.AddListener(this);
    }

    bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
    {
        return true;
    }
}

未调用ReceiveWeakEvent方法。调用OnCompositionTargetRendering，但似乎DeliverEvent不能像我预期的那样工作。将侦听器添加到Button.Click等实例事件中工作正常... 测试项目在.NET 4.0 Client Profile上。

A post on Microsoft Connect from 2009表示不支持静态事件，但我检查了WeakEventManager源代码，它看起来没问题：

    protected void ProtectedAddListener(object source, IWeakEventListener listener) 
    { 
        Debug.Assert(listener != null, "Listener cannot be null");

        object sourceKey = (source != null) ? source : StaticSource;
        ...
    }

Answer 1

自己弄清楚：将DeliverEvent方法的 sender 参数更改为null：

void OnCompositionTargetRendering(object sender, EventArgs e)
{
    this.DeliverEvent(null, e);
}

将WeakEventManager与静态事件一起使用

1 个答案: