带有列表视图的 ReactiveUI 6 未更新

Question

一直在修改响应式用户界面，并尝试让一个简单的示例在通用应用程序中运行并有一些差异。

我的视图模型为：

public class Rooms : ReactiveObject
{
    private RoomsService roomService;
    private IReactiveCommand<IList<Room>> fetchRooms;

    private ObservableAsPropertyHelper<IList<Room>> myRooms;
    public IList<Room> MyRooms
    {
        get { return myRooms.Value; }
    }

    public Rooms(RoomsService roomsService)
    {
        this.RoomService = roomsService;
        fetchRooms = ReactiveCommand.CreateAsyncTask<IList<Room>>(Observable.Return<bool>(true), async x => await RoomService.Rooms);
        fetchRooms.Subscribe(_ => LogMessage("Cool, it was invoked!"));
        fetchRooms.ToProperty(this, x => x.MyRooms, out myRooms);

    }

    public RoomsService RoomService
    {
        get { return roomService; }
        set { roomService = value; }
    }
}

正在获取信息的服务是：

public class RoomsService
{
    private FakeRoomService service = new FakeRoomService();

    public IObservable<IList<Room>> Rooms
    {
        get
        {
            LogMessage("RoomsService - Rooms property called.");
            return Observable
                .Interval(TimeSpan.FromSeconds(1))
                .Select(_ => service.GetRoomsForUser());
        }
    }
}

后面有基本代码：

public sealed partial class HubPage : Page
{
    private NavigationHelper navigationHelper;
    private Rooms rooms = new Rooms(new RoomsService());

    /// <summary>
    /// Gets the NavigationHelper used to aid in navigation and process lifetime management.
    /// </summary>
    public NavigationHelper NavigationHelper
    {
        get { return this.navigationHelper; }
    }

    /// <summary>
    /// Gets the rooms view model.
    /// </summary>
    public Rooms Rooms
    {
        get { return this.rooms; }
    }

    public HubPage()
    {
        this.InitializeComponent();
        this.navigationHelper = new NavigationHelper(this);
        this.navigationHelper.LoadState += this.NavigationHelper_LoadState;
    }

以及最终的 xaml：

<Page
x:Name="pageRoot"
x:Class="HubPage"
DataContext="{Binding Rooms, RelativeSource={RelativeSource Self}}"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Hub"
xmlns:data="using:Hub.Data"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Hub SectionHeaderClick="Hub_SectionHeaderClick">
        <HubSection Width="500" x:Uid="Section1Header" Header="Section 1">
            <DataTemplate>
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="300" />
                    </Grid.RowDefinitions>

                    <ListView Name="RoomListView" Grid.Row="1" ItemsSource="{Binding MyRooms}">
                        <ListView.ItemTemplate>
                            <DataTemplate>
                                <TextBlock Text="{Binding Name}" FontWeight="Bold" />
                            </DataTemplate>
                        </ListView.ItemTemplate>
                    </ListView>
                </Grid>
            </DataTemplate>
        </HubSection>         
    </Hub>
</Grid>

我显然在视图模型中遗漏了一些明显的东西，但我不确定它是什么。任务似乎结束了，但属性永远不会更新......或者如果更新了，它不会传播到视图？

任何建议或是否有任何地方的 v6 的非常简单的工作示例？

Answer 1

如果你await 和Observable，大致相当于在 Rx 中：

someObservable.TakeLast(1).Publish(new AsyncSubject<T>()).Subscribe();

这就是问题所在，请查看您的 Observable：

return Observable
    .Interval(TimeSpan.FromSeconds(1))
    .Select(_ => service.GetRoomsForUser());

它永远不会终止，所以TakeLast 永远不会返回！

做什么？

相反，我们应该写：

fetchRooms = ReactiveCommand.CreateAsyncTask<IList<Room>>(_ => Task.Run(service.GetRoomsForUser());

然后在 View 代码隐藏中，我们可以设置计时器来调用命令：

Observable.Interval(TimeSpan.FromSeconds(5), RxApp.MainThreadScheduler)
    .InvokeCommand(this, x => x.ViewModel.FetchRooms);

为什么是 View 代码隐藏？

在 ViewModel 构造函数中设置计时器并调用 Do Stuff 的命令使得测试变得困难，因为您必须部署 3032x 模拟来阻止一堆事情的发生。

相反，View 构造函数应该进入 VM 以启动这些操作，并且 VM 测试可以在他们想要显式测试它们时调用它们。