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

Question

为什么要task永远等待？:

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上设置一个断点并点击它.但task.Wait()永远不会动.

更好的更新: FirstAsync()我正在寻找:

    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();
    }

在哪里GetCommunicatorObservableForPushMessageReceived():

    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(但它确实有效):

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;
}

Answer 1

无论RunAsync和ToTask产生的最后的值中观察到.因此,在观察完成之前不会产生任何价值.但是创建的可观察量FromEventPattern通常不会完成.你需要强迫他们喜欢的东西来完成Take或Until.

我还会注意到这一点RunAsync并且ToTask本质上是多余的,并且不需要同时执行这两项操作.

在你的情况下,我假设你真的对通过你的过滤器的第一个值感兴趣:

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

task.Wait();