Question

我已经实现了这个WeakEvent委托，但由于某种原因它只能工作几秒钟，之后它就会停止工作：

public class WeakEventHandler<TE>  where TE : EventArgs
{
    private readonly Action<WeakEventHandler<TE>> _unsubscriber;
    private readonly WeakReference<EventHandler<TE>> _targetRef;
    private readonly EventHandler<TE> _handler;


    public WeakEventHandler(EventHandler<TE> eventReceiver, Action<WeakEventHandler<TE>> unsubscriber)
    {
        _unsubscriber = unsubscriber;
        _targetRef = new WeakReference<EventHandler<TE>>(eventReceiver);
        _handler = Invoke;
    }

    public void Invoke(object sender, TE e)
    {
        EventHandler<TE> method;

        if (_targetRef.TryGetTarget(out method))
        {
            method(sender, e);
        }
        else
        {
            _unsubscriber(this);
        }

    }

    public static implicit operator EventHandler<TE>(WeakEventHandler<TE> weh)
    {
        return weh._handler;
    }
}

public static class EventHandlerUtils
{
    public static EventHandler<TE> MakeWeak<TE>(this EventHandler<TE> eventReceiver, Action<WeakEventHandler<TE>> unsubscriber) where TE : EventArgs
    {
        return new WeakEventHandler<TE>(eventReceiver, unsubscriber);
    }
}

用法：

    private EventHandler<MouseInteractionArgs> _mouseInteractionDelegate;

    public event EventHandler<MouseInteractionArgs> MouseAction
    {
        add
        {
            _mouseInteractionDelegate += value.MakeWeak(handler => _mouseInteractionDelegate -= handler );
        }

        remove
        {
            throw new InvalidOperationException("This is a weak Event, dont worry about unsubscribing");
        }
    }

我从不停止引用该方法的所有者，因此我不知道它为什么不起作用，委托的行为是否不同？

Answer 1

但是＆＃34; eventreceiver＆＃34;由方法实例拥有

对不起，但你有倒退了。＆＃34; eventReceiver＆＃34;是要添加到MouseAction事件的委托实例。该委托实例保留对目标对象和MethodInfo的引用，而不是相反。除了WeakReference之外，没有代码保留对委托实例的引用，当然还有设计不足以使对象保持活动状态。

Answer 2

根据你的回答，我能够修复Weakeventhandler：

public class WeakEventHandler<TE> where TE : EventArgs
{
    private delegate void OpenEventHandler(object target, object sender, TE e);

    private readonly WeakReference _targetRef;
    private readonly OpenEventHandler _openHandler;

    private readonly Action<WeakEventHandler<TE>> _unsubscriber;
    private readonly EventHandler<TE> _handler;


    public WeakEventHandler(EventHandler<TE> subscriber, Action<WeakEventHandler<TE>> unsubscriber)
    {
        _unsubscriber = unsubscriber;
        _targetRef = new WeakReference(subscriber.Target);
        _handler = Invoke;


        var target = Expression.Parameter(typeof (object), "target");
        var sender = Expression.Parameter(typeof(object), "sender");
        var args = Expression.Parameter(typeof (TE), "args");

        _openHandler =
            Expression.Lambda<OpenEventHandler>(
                Expression.Call(Expression.Convert(target, subscriber.Target.GetType()), subscriber.Method, sender,
                    args),target,sender,args).Compile();
    }

    public void Invoke(object sender, TE e)
    {
        var t = _targetRef.Target;

        if (t != null)
        {
            _openHandler(t, sender, e);
        }
        else
        {
            _unsubscriber(this);
        }

    }

    public static implicit operator EventHandler<TE>(WeakEventHandler<TE> weh)
    {
        return weh._handler;
    }
}

我正在构建一个基于组件的系统，其中Object的组件有时需要与例如鼠标事件进行交互，我不希望为每个从世界中删除的对象取消注册每个组件。

WeakReference太弱了？

2 个答案: