this.WhenAnyValue(...).InvokeCommand not always invoked in main thread

[Atle]

Hi!

I have a Reactive command which reads a bunch of data and tries to create SciChart renderable series. The SciChart classes must be created in the UI thread. I invoke the command using:

this.WhenAnyValue(x => x.SelectedAnalysis)

     .Throttle(TimeSpan.FromSeconds(1), RxApp.MainThreadScheduler)

     .ObserveOn(RxApp.MainThreadScheduler)

     .InvokeCommand(this, x => x.CreateSeries);

However, the command is not always invoked on the main thread. Especially if the SelectedAnalysis property is changed multiple times within a second:

CreateSeries = ReactiveCommand.CreateAsyncTask(

                async _ =>

                {

                    IScoreAnalysisSetup setup = ActiveSetup;

                    Tuple<ScoreAnalysisIdentifier, ScoreAnalysisProperty> selectedAnalysis = SelectedAnalysis;

                    if (setup == null || selectedAnalysis == null)

                        return;

                    PlotData truthData = await CreateTruthSeriesAsync(setup, selectedAnalysis);

                    IList<PlotData> plotDatas = new List<PlotData>();

                    plotDatas.Add(truthData);

STA crash-->var chartViewModels = plotDatas.Select(CreateIncludedTruthSeries).ToList();

                    SetSeriesCollection(chartViewModels);

                });

What am I doing wrong? I have tried returning the PlotData list from the command and subscribe like this:

            CreateSeries.ObserveOn(RxApp.MainThreadScheduler)

                        .Subscribe(x =>

            {

                if (x == null)

                {

                    SetSeriesCollection();

                    return;

                }

                var chartViewModels = x.Select(CreateIncludedTruthSeries).ToList();

                SetSeriesCollection(chartViewModels);

            });

However, this does not help at all. Still things are being invoked on a background thread.

Sincerely

Atle

[paul....@gmail.com]

Hey Atle,

What thread this ends up on depends on the implementation of CreateTruthSeriesAsync. In that async block though, you need to not touch any UI elements or things bound to UI elements. Subscribe to the command and mutate UI elements there

Paul

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[Atle]

Hi Paul,

CreateTruthSeriesAsync is only reading data and putting it in that PlotData class. Then, below the call to that function, i expect to be back on the UI thread, however, this is not always the case. The line "var chartViewModels = plotDatas.Select(CreateIncludedTruthSeries).ToList();" must be run on the UI thread, but throws an exception when not. There seems to be something wrong with the RxApp.MainThreadScheduler. When setting it manually things are working better. 

            RxApp.MainThreadScheduler = DispatcherScheduler.Current;

            RxApp.TaskpoolScheduler = TaskPoolScheduler.Default;

It might be worth to mention that I have compiled ReactiveUI from source and strong-named the dlls due to my application being a plug-in to another. Maybe I have forgotten something here? This is a Windows WPF application by the way.

- Atle