ReactiveUI 6 异步命令未在 WPF 应用中的后台线程上运行

ViewModel

public class MyViewModel:ReactiveObject, IRoutableViewModel{
        private ReactiveList<string> _appExtensions; 
        public MyViewModel(IScreen screen){
            HostScreen = screen;
            AppExtensions = new ReactiveList<string>();
            GetApplicationExtensions =
                ReactiveCommand.CreateAsyncTask(x => _schemaService.GetApplicationExtensions()); // returns a Task<IEnumerable<string>>
            GetApplicationExtensions
                .ObserveOn(RxApp.MainThreadScheduler)
                .SubscribeOn(RxApp.TaskpoolScheduler)
                .Subscribe(p =>
                {
                    using (_appExtensions.SuppressChangeNotifications())
                    {
                        _appExtensions.Clear();
                        _appExtensions.AddRange(p);
                    }
                });
            GetApplicationExtensions.ThrownExceptions.Subscribe(
                ex => Console.WriteLine("Error during fetching of application extensions! Err: {0}", ex.Message));
        }
        // bound to a ListBox 
        public ReactiveList<string> AppExtensions
        {
            get { return _appExtensions; }
            set { this.RaiseAndSetIfChanged(ref _appExtensions, value); }
        } 
       public ReactiveCommand<IEnumerable<string>> GetApplicationExtensions { get; protected set; }
}

并且视图有一个<Button Command="{Binding GetApplicationExtensions}"></Button>.

GetApplicationExtensions的内涵

    public async Task<IEnumerable<string>> GetApplicationExtensions()
    {
        IEnumerable<string> extensions = null;
        using (var client = new HttpClient())
        {
            client.BaseAddress = BaseAddress;
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", _accessToken);
            var response = await client.GetAsync("applications");
            if (response.IsSuccessStatusCode)
            {
                var json = await response.Content.ReadAsStringAsync();
                extensions = JsonConvert.DeserializeObject<IEnumerable<string>>(json);
            }
        }
        return extensions;
    }

从我读到的关于 ReactiveUI 的所有内容和我看到的所有示例(尽管新的 6.0+ 版本很少(，这应该使我的异步调用(通过 HttpClient 发出异步 HTTP 请求(在后台线程上运行，并在返回结果时更新我视图中的ListBox。但是，情况并非如此 - UI 在异步调用期间被锁定。我做错了什么？

更新

如果我将我的 HTTP 调用包装在Task那么一切都按预期工作 - UI 根本没有挂起。所以我的服务调用的新实现是这样的：

    public Task<IEnumerable<string>> GetApplicationExtensions()
    {
        var extensionsTask = Task.Factory.StartNew(async () =>
        {
             IEnumerable<string> extensions = null;
             using (var client = new HttpClient())
             {
                 client.BaseAddress = BaseAddress;
                 client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", _accessToken);
                 var response = await client.GetAsync("applications");
                 if (response.IsSuccessStatusCode)
                 {
                     var json = await response.Content.ReadAsStringAsync();
                     extensions = JsonConvert.DeserializeObject<IEnumerable<string>>(json);
                 }
             }
             return extensions;
        }
        return extensionsTask.Result;
    }

此外，通过对异步服务调用的更改，我可以像@PaulBetts一样从ReactiveCommand中删除ObserveOn和SubscribeOn。所以我在视图模型的构造函数中的ReactiveCommand实现变成了这样：

            GetApplicationExtensions =
                ReactiveCommand.CreateAsyncTask(x => _schemaService.GetApplicationExtensions()); // returns a Task<IEnumerable<string>>
            GetApplicationExtensions
                .Subscribe(p =>
                {
                    using (_appExtensions.SuppressChangeNotifications())
                    {
                        _appExtensions.Clear();
                        _appExtensions.AddRange(p);
                    }
                });