Manually clearing an Android ViewModel?

Question

Edit: This question is a bit out of date now that Google has given us the ability to scope ViewModel to navigation graphs. The better approach (rather

Answer 1

In my case, most of the things I observe are related to the Views, so I don't need to clear it in case the View gets destroyed (but not the Fragment).

In the case I need things like a LiveData that takes me to another Fragment (or that does the thing only once), I create a "consuming observer".

It can be done by extending MutableLiveData:

fun  MutableLiveData.observeConsuming(viewLifecycleOwner: LifecycleOwner, function: (T) -> Unit) {
    observe(viewLifecycleOwner, Observer {
        function(it ?: return@Observer)
        value = null
    })
}

and as soon as it's observed, it will clear from the LiveData.

Now you can call it like:

viewModel.navigation.observeConsuming(viewLifecycleOwner) { 
    startActivity(Intent(this, LoginActivity::class.java))
}