ReactiveUI ObservableAsPropertyHelper性能

Question

代码：

public class AppViewModel : ReactiveObject
{
    public AppViewModel()
    {
        Observable.Timer(TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(1), RxApp.MainThreadScheduler)
        .Do(_ => Score++)
        .Subscribe();
    }

    private long _score;
    public long Score
    {
        get => _score;
        set => this.RaiseAndSetIfChanged(ref _score, value);
    }
}

在功能上等同于：

public class AppViewModel : ReactiveObject
{
    private readonly ObservableAsPropertyHelper<long> _score;

    public AppViewModel()
    {
        _score =
            Observable
            .Timer(TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(1), RxApp.MainThreadScheduler)
            .ToProperty(this, x => x.Score);
    }

    public long Score => _score.Value;
}

虽然，在第二种情况下，在开始计数之前有一个明显的延迟(在我的机器上超过一秒)。导致这种情况的原因是什么？

为了完整性：

MainWindow.xaml

<reactiveui:ReactiveWindow 
    x:Class="ReactiveDemo.MainWindow"
    x:TypeArguments="reactivedemo:AppViewModel"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:reactivedemo="clr-namespace:ReactiveDemo"
    xmlns:reactiveui="http://reactiveui.net"
    Title="Rx" Height="450" Width="800"
    mc:Ignorable="d">
    <Viewbox>
        <Label x:Name="ScoreLabel" ContentStringFormat="D2" FontFamily="Lucida Console" />
    </Viewbox>
</reactiveui:ReactiveWindow>

MainWindow.xaml.cs

using ReactiveUI;
using System.Reactive.Disposables;

namespace ReactiveDemo
{
    public partial class MainWindow : ReactiveWindow<AppViewModel>
    {
        public MainWindow()
        {
            InitializeComponent();

            ViewModel = new AppViewModel();

            this.WhenActivated(disposableRegistration =>
            {
                this.OneWayBind(ViewModel,
                    viewModel => viewModel.Score,
                    view => view.ScoreLabel.Content)
                    .DisposeWith(disposableRegistration);
            });
        }
    }
}

Answer 1

您正在使用的ToProperty重载具有反射开销。试试ToProperty(this, nameof(Score))。可能仍然会影响性能，因为ToProperty所做的比您发布的功能等价的功能要多一点。