CODEWITHSUNDEEP
c#wpfdata-bindingreactiveui
Funk
Funk

Reputation: 11221

ReactiveUI ObservableAsPropertyHelper performance

The code:

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);
    }
}

Is functionally equivalent to:

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;
}

Although, in the second case, there's a noticeable delay (of over a second on my machine) before counting starts. What would be the cause of this?

For completeness:

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);
            });
        }
    }
}

Upvotes: 0

Views: 413

Answers (1)

Rodney Littles
Rodney Littles

Reputation: 564

The ToProperty overload that you are using has a reflection cost. Try ToProperty(this, nameof(Score)). There may still be a performance hit as the ToProperty does a bit more than the functional equivalent you've posted.

Upvotes: 1

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