c# - IObservable <T> .ToTask <T>方法返回等待激活的任务

为什么task永远等待着呢？:

var task = Observable
    .FromEventPattern<MessageResponseEventArgs>(communicator, "PushMessageRecieved")
    .Where(i => i.EventArgs.GetRequestFromReceivedMessage().Name == requestName)
    .Select(i => i.EventArgs)
    .RunAsync(System.Threading.CancellationToken.None)
    .ToTask();

task.Wait();

我知道"PushMessageRecieved"被解雇了；我可以在Select lambda上设置一个断点，然后点击它。但是task.Wait()永远不会动。

更好的更新: FirstAsync()是我想要的:

    public static Task<MessageResponseEventArgs> HandlePushMessageRecievedAsync(this ICommunicator communicator, RequestName requestName)
    {
        if (communicator == null) return Task.FromResult<MessageResponseEventArgs>(null);

        var observable = GetCommunicatorObservableForPushMessageReceived(communicator);
        return observable
            .Where(i => i.GetRequestFromReceivedMessage().Name == requestName)
            .Select(i => i)
            .FirstAsync()
            .ToTask();
    }

其中GetCommunicatorObservableForPushMessageReceived()是:

    static IObservable<MessageResponseEventArgs> GetCommunicatorObservableForPushMessageReceived(ICommunicator communicator)
    {
        if (communicatorObservableForPushMessageReceived == null)
        {
            communicatorObservableForPushMessageReceived = Observable
                .FromEventPattern<MessageResponseEventArgs>(communicator, "PushMessageRecieved")
                .Where(i => !IsPreviousMessage(i.EventArgs.GetRequestFromReceivedMessage().EventId))
                .Select(i => i.EventArgs);
        }

        return communicatorObservableForPushMessageReceived;
    }

更新:这有点可怕(但它可以工作):

public static Task<MessageResponseEventArgs> HandlePushMessageRecievedAsync(this ICommunicator communicator, RequestName requestName)
{
    if (communicator == null) return Task.FromResult<MessageResponseEventArgs>(null);

    var completionSource = new TaskCompletionSource<MessageResponseEventArgs>();

    Observable
        .FromEventPattern<MessageResponseEventArgs>(communicator, "PushMessageRecieved")
        .Where(i => i.EventArgs.GetRequestFromReceivedMessage().Name == requestName)
        .Select(i => i.EventArgs)
        .ToEvent().OnNext += (args) =>
        {
            if (args.Response.Errors != null && args.Response.Errors.Any())
            {
                completionSource.TrySetException(args.Response.Errors.Select(j => new Exception(j.ErrorMessage)));
            }
            else
            {
                completionSource.TrySetResult(args);
            }
        };

    return completionSource.Task;
}

最佳答案

RunAsync和ToTask都产生可观察值中的最后一个值。因此，直到可观察结果完成，将不会产生任何值(value)。但是用FromEventPattern创建的可观察对象通常不会完成。您需要强制他们使用Take或Until之类的内容来完成操作。

我还将注意到RunAsync和ToTask本质上是多余的，不需要两者都做。

对于您的情况，我假设您对通过过滤器进行过滤的第一个值非常感兴趣:

var task = Observable
    .FromEventPattern<MessageResponseEventArgs>(communicator, "PushMessageRecieved")
    .FirstAsync(i => i.EventArgs.GetRequestFromReceivedMessage().Name == requestName)
    .Select(i => i.EventArgs)
    .ToTask();

task.Wait();