AutoRefreshOnObservable only works once. Why? - wpf

Question

I'm working on a small programm where i'm evaluating if reactive ui is the right framework for another project. So far so good... At the moment i'm a little bit lost in a DynamicData related function. I'm trying to execute a command in the MainViewWindow every time a combo box in a ReactiveUserControl is changed. All my Models are extending ReactiveObject and the Properties are set up with the RaiseAndSetIfChanged setter.
In my ReactiveUserControl ViewModel I invoke my Command SaveImage from the ReactiveUserControl ViewModel as it is described here:
https://reactiveui.net/docs/handbook/message-bus/#ways-to-avoid-using-messagebus
Defining the ObservableCollection
public ObservableCollection<FileViewModel> VisibleFiles { get; protected set; }
Initialize the Collection, Files is a SourceList
WatchFiles = ReactiveCommand.Create(() =>
{
VisibleFiles = new ObservableCollection<FilesViewModel>(Files.Items);
VisibleFiles.ToObservableChangeSet().AutoRefreshOnObservable(doc => doc.SaveImage).Select(_ => WhenAnyFileChanged()).Switch().Subscribe<FilesViewModel>(x => {
Console.WriteLine("HOORAY");
});
});
private IObservable<FilesViewModel> WhenAnyFileChanged()
{
return VisibleFiles.Select(x => x.SaveFile.Select(_ => x )).Merge();
}
The First time a combo box changed it gets evaluated correct. I get the "Hooray". But every time after that there is no output. If I invoke the Watch Files Command again it is again working once.
Why is this happening, and how can i solve it to print every time a file changed the "Hooray" ? I can see, that the ObservableCollection detects the change, and also the Command in the ReactiveUserControl is invoked on the change. But the WhenAnyFileChanged Method doesn't return the changed element after the first invokation.
Hopefully it is understandable what I'm trying to achieve, an what's the problem.
Update: I don't know why, but if i check the ChangeSet in the Select() i get TotalChanges 10 at initialisation, which is right. Then with my first working change TotalChanges is 0 but is evaluated right. On my next attempt on changing i still get 0 TotalChanges but also no correct evaluation in WhenAnyFileChanged().
Refreshes() is 1 on every change.
Update 2: Changing AutoRefreshOnObservable() to AutoRefresh() brings the desired functionality.

Answer 1

I copied the original message bus example and wrote a unit test to see whether the code behaves as expected. I can confirm the issue you are seeing is present in the example. The following code only fires once.
public MainViewModel()
{
OpenDocuments = new ObservableCollection<DocumentViewModel>();
OpenDocuments
.ToObservableChangeSet()
.AutoRefreshOnObservable(document => document.Close)
.Select(_ => WhenAnyDocumentClosed())
.Switch()
.Subscribe(x => OpenDocuments.Remove(x), ex=>{},()=>{});
}
IObservable<DocumentViewModel> WhenAnyDocumentClosed()
{
return OpenDocuments
.Select(x => x.Close.Select(_ => x))
.Merge();
}
And here's the test to prove it. It fails on the second attempt to remove.
[Fact]
public void MyTest()
{
//I added an id field to help with diagnostics / testing
_mainViewModel.OpenDocuments.Count.Should().Be(4);
_mainViewModel.OpenDocuments.Any(dvm => dvm.Id == "1").Should().BeTrue();
_mainViewModel.OpenDocuments[0].Close.Execute().Subscribe();
_mainViewModel.OpenDocuments.Count.Should().Be(3);
_mainViewModel.OpenDocuments.Any(dvm => dvm.Id == "1").Should().BeFalse();
_mainViewModel.OpenDocuments[0].Close.Execute().Subscribe();
_mainViewModel.OpenDocuments.Count.Should().Be(2);
_mainViewModel.OpenDocuments.Any(dvm => dvm.Id == "2").Should().BeFalse();
}
I am unsure why this fails, but the most optimal fix is to make use of Dynamic Data's MergeMany operator which is similar to Rx's Merge but automatically wires observables when items are added to the underlying list and unwires them when items are removed. The fix is:
public class MainViewModel : ReactiveObject
{
public ObservableCollection<DocumentViewModel> OpenDocuments { get;}
public MainViewModel()
{
OpenDocuments = new ObservableCollection<DocumentViewModel>();
OpenDocuments
.ToObservableChangeSet()
.MergeMany(x => x.Close.Select(_ => x))
.Subscribe(x => OpenDocuments.Remove(x));
}
}
Running the same unit tests pass.
The code with unit test is available in this gist