Question

在rx中你可以写：

var oe = Observable.FromEventPattern<SqlNotificationEventArgs>(sqlDep, "OnChange");

然后订阅observable以将sqlDep对象上的OnChange事件转换为observable。

类似地，如何使用任务并行库从C＃事件创建任务？

编辑：澄清 Drew指向的解决方案然后由user375487明确地书写，适用于单个事件。任务一完成......好了就完了。

可观察事件可以随时再次触发。它可以被视为一个可观察的流。 TPL数据流中的一种ISourceBlock。但是在文档http://msdn.microsoft.com/en-us/library/hh228603(v=vs.110).aspx中没有ISourceBlock的例子。

我最终找到了一篇论坛帖子，解释了如何做到这一点：http://social.msdn.microsoft.com/Forums/en/tpldataflow/thread/a10c4cb6-868e-41c5-b8cf-d122b514db0e

public static ISourceBlock CreateSourceBlock（动作，行动，行动，ISourceBlock＆GT;执行人） { var bb = new BufferBlock（）; 执行者（t =＆gt; bb.Post（t），（）=＆gt; bb.Complete（），e =＆gt; bb.Fault（e），bb）; 返回bb; }

//Remark the async delegate which defers the subscription to the hot source. var sourceBlock = CreateSourceBlock<SomeArgs>(async (post, complete, fault, bb) => { var eventHandlerToSource = (s,args) => post(args); publisher.OnEvent += eventHandlerToSource; bb.Complete.ContinueWith(_ => publisher.OnEvent -= eventHandlerToSource); });

~~我没试过上面的代码。异步委托和CreateSourceBlock的定义之间可能存在不匹配。~~

Answer 1

没有与TPL中的事件异步模式（EAP）直接等效。你需要做的是使用你在事件处理程序中发出信号的TaskCompletionSource<T>。 Check out this section on MSDN示例使用WebClient :: DownloadStringAsync来演示模式。

Answer 2

您可以使用TaskCompletionSource。

public static class TaskFromEvent
{
    public static Task<TArgs> Create<TArgs>(object obj, string eventName)
        where TArgs : EventArgs
    {
        var completionSource = new TaskCompletionSource<TArgs>();
        EventHandler<TArgs> handler = null;

        handler = new EventHandler<TArgs>((sender, args) =>
        {
            completionSource.SetResult(args);
            obj.GetType().GetEvent(eventName).RemoveEventHandler(obj, handler);
        });

        obj.GetType().GetEvent(eventName).AddEventHandler(obj, handler);
        return completionSource.Task;
    }
}

使用示例：

public class Publisher
{
    public event EventHandler<EventArgs> Event;

    public void FireEvent()
    {
        if (this.Event != null)
            Event(this, new EventArgs());
    }
}

class Program
{
    static void Main(string[] args)
    {
        Publisher publisher = new Publisher();
        var task = TaskFromEvent.Create<EventArgs>(publisher, "Event").ContinueWith(e => Console.WriteLine("The event has fired."));
        publisher.FireEvent();
        Console.ReadKey();
    }
}

编辑根据您的说明，以下是如何使用TPL DataFlow实现目标的示例。

public class EventSource
{
    public static ISourceBlock<TArgs> Create<TArgs>(object obj, string eventName)
        where TArgs : EventArgs
    {
        BufferBlock<TArgs> buffer = new BufferBlock<TArgs>();
        EventHandler<TArgs> handler = null;

        handler = new EventHandler<TArgs>((sender, args) =>
        {
            buffer.Post(args);
        });

        buffer.Completion.ContinueWith(c =>
            {
                Console.WriteLine("Unsubscribed from event");
                obj.GetType().GetEvent(eventName).RemoveEventHandler(obj, handler);
            });

        obj.GetType().GetEvent(eventName).AddEventHandler(obj, handler);
        return buffer;
    }
}

public class Publisher
{
    public event EventHandler<EventArgs> Event;

    public void FireEvent()
    {
        if (this.Event != null)
            Event(this, new EventArgs());
    }
}

class Program
{
    static void Main(string[] args)
    {
        var publisher = new Publisher();
        var source = EventSource.Create<EventArgs>(publisher, "Event");
        source.LinkTo(new ActionBlock<EventArgs>(e => Console.WriteLine("New event!")));
        Console.WriteLine("Type 'q' to exit");
        char key = (char)0;
        while (true)
        {
            key = Console.ReadKey().KeyChar;             
            Console.WriteLine();
            if (key == 'q') break;
            publisher.FireEvent();
        }

        source.Complete();
        Console.ReadKey();
    }
}

什么是rx的Observable.FromEventPattern的TPL等价物？

2 个答案: