c# - 为什么SubscribeOn在这里不能作为扩展方法而是直接调用？

Question

我有ObserverBase类。在Start方法中，我订阅了一个可观察对象，应用了转换和过滤器。

我不明白为什么未编译SubscribeOn作为扩展方法的用法。
谁能解释这种行为？

public class ObserverBase<T1, T2> : IPeer<T1, T2>
{

    private readonly ISubject<T2> subject;

    private readonly IMapper<T1, T2> messageMapper;

    protected ObserverBase(ISubject<T2> subject, IMapper<T1, T2> messageMapper)
    {
        this.subject = subject;
        this.messageMapper = messageMapper;
    }

    public IObservable<T2> Start(IObservable<T1> observable, Func<T2, bool> predicate)
    {
        //works
        Synchronization.ObserveOn(Synchronization.SubscribeOn(observable, TaskPoolScheduler.Default),
                                  Scheduler.Immediate)
                  .Select(message => this.messageMapper.Map(message))
                  .Where(predicate)
                  .Subscribe(observation => this.subject.OnNext(observation));


        // compile error on SubscribeOn: The type arguments cannot be inferred from the usage. Try specifying the type argument explicitly.
        observable.SubscribeOn(TaskPoolScheduler.Default).ObserveOn(Scheduler.Immediate)
                  .Select(message => this.messageMapper.Map(message))
                  .Where(predicate)
                  .Subscribe(observation => this.subject.OnNext(observation));

        // compile error on TaskPoolScheduler.Default: Cannot resolve method SubscribeOn(System.Reactive.Concurrency.TaskPoolScheduler)
        observable.SubscribeOn<T1>(TaskPoolScheduler.Default).ObserveOn(Scheduler.Immediate)
                  .Select(message => this.messageMapper.Map(message))
                  .Where(predicate)
                  .Subscribe(observation => this.subject.OnNext(observation));

        return this.subject;
    }
}

Answer 1

这对我有用-您是否为using命名空间(定义了System.Reactive.Linq)包括了SubscribeOn语句？ Synchronization.ObserveOn在另一个 namespace (System.Reactive.Concurrency)中-我怀疑您已经有了using语句。