Hey guys, I am using `MutableStateFlow` in my project. When we initialise the `MutableStateFlow` obj...

# flow

[Vivek Modi]

Hey guys, I am using MutableStateFlow in my project. When we initialise the MutableStateFlow object we need to give default value.

val topics = MutableStateFlow<List<String>>(emptyList())

when I collect this value

[null, "Hello", "world"]

I want to pass this list in adapter . So is there a way we can remove the null object before passing in adapter or Is there any better way ?

viewModel.topics.collect { topicsList ->
    println(topicsList)         // [null, "Hello", "world"]
    adapter.submitList(topicsList)
}

[Desmond Teo]

is this what you want?

adapter.submitList(topicsList.filterNotNull())

[Vivek Modi]

Yes but if I add this line is do again check in whole list ?

[Vivek Modi]

So does it impact on performance?

[Erick Sumargo]

I think you always need to filter those null value manually because it came from the data source (I suppose?).

Also if you concern with the performance, perhaps you can move the filter computation to other dispatcher first. Something like this:

viewModel.topics
    .filter { ... }
    .flowOn(Dispatcher.Default)
    .collect { ... }

[Vivek Modi]

Okk great. Thanka

[DALDEI]

I would be interested in how this turns out.
My guess is that adding flowOn() actually takes longer (in terms of CPU time used on main thread)
due to the overhead of having to dispatch in and out of another thread each time vs simply comparing for nulls
It would depend on how big topicList is. My 'guess' is that it would take a list > several 1000's long before it was
less time (cpu time used in main thread) to switch threads and back vs filtering inline .