ReactiveUI CombineLatest not trigger Func - wpf

Question

I am using ReactiveUI in WPF. I bind one ListBox.ItemSource to my ViewModel.FileList.
The below Observable.CombinedLatest() doesn't trigger the Func.
But the above single Observable trigger its Func.
The reason I want to use combined observable is:
I would like to display a list of data on the first time load - this is triggered by the ConvertedMessage property value changed.
Then I also need display different list when user enter the words on the search textbox, both of them actually update the same DataBinding Source List.
I also tried two different individual observables, two separate Methods in the Observable.SelectMany(MyMethod), but seems the second observable override the previous one - because only the last observable.MyMethod called.
Is there any idea or suggestion regarding the ReactiveUI CombinedLatest(), is it only trigger the function when all observables produce the element?
this.WhenAnyValue(x => x.ConvertedMessage).Where(x=>x!=null).Subscribe(x => { var msg = x.Message; });
var initial =
this
.WhenAnyValue(x => x.ConvertedMessage)
.Where(x=>x!=null);
var searchObjs =
this
.WhenAnyValue(x => x.SearchText)
.Throttle(TimeSpan.FromMilliseconds(800))
.Select(term => term)
.DistinctUntilChanged()
.Where(term => !string.IsNullOrEmpty(term));
reviewFiles = Observable.CombineLatest(initial, searchObjs, (message, term) => {
ObservableCollection<PrecedentFile> loadedFiles = new ObservableCollection<PrecedentFile>();
var start = 0;
CurrentPage = 1;
if (!string.IsNullOrEmpty(term))
{
//some logic
return searchedResults;
}
else
{
//other logic
return loadedFiles.AsEnumerable<PrecedentFile>();
}
}).Select(x=>x)
.ObserveOn(RxApp.MainThreadScheduler)
.ToProperty(this, x => x.ReviewFiles);

Answer 1

I believe the problem you are facing is the CombineLatest needs all observables passed into it to have at least had event/signals occurred at least once.
In your example above if initial has a trigger but searchObs does not, then the CombineLatest won't fire.
Eg you've had the ConvertedMessage be changed 3 times, but SearchText has never been changed, then the CombineLatest will not fire.
One thing you could do is remove the .Where(x => x != null) and Where(term => !string.IsNullOrEmpty(term)) statements and handle those conditions in your CombineLatest lambda. WhenAnyValue() will be default signal with the initial value of your properties (which is often null). That way both sides have already had a value signalled.