Should I share my ViewModel across two fragments?

Question

I'm attempting to follow Android best practices and use the latest recommended architecture components. You can see my attempt so far here: https://github.com/randroid88/TodayILearned

Right now the app's features are very limited.

It has a Room db for locally storing journal entries.
One fragment, HomeFragment, that lists all the entries
Another fragment, EntryEditorFragment, that creates new entries.
A ViewModel, EntryViewModel, that updates the data via a repository.

The problem is that only HomeFragment has access to EntryViewModel right now.

So in my current design, I pass the new entry text from EntryEditorFragment to HomeFragment via an argument bundle (using SafeArgs from the new Navigation Architecture Component), then HomeFragment creates the new entry via the EntryViewModel:

val safeArgs = HomeFragmentArgs.fromBundle(arguments!!)
    savePossibleNewEntry(safeArgs.entryText)

private fun savePossibleNewEntry(entryText: String) {
    entryViewModel!!.insert(EntryCreator().create(entryText))
}

This doesn't feel right.

Would it be better if EntryViewModel also had access to EntryEditorFragment?

In order to accomplish this, would I have to scope the ViewModel to the Activity as explained here on this blog?

What is the best practice here?

It does look like the official documentation recommends sharing the ViewModel: https://developer.android.com/topic/libraries/architecture/viewmodel#sharing_data_between_fragments — Randy, Dec 31 '18 at 23:13

score 2 · Accepted Answer · answered Jan 01 '19 at 04:47

The Android documentation suggested sharing a ViewModel for "a common case of master-detail fragments" so I decided to do the same for my case.

As suggested, I scoped the ViewModel to the Activity in both fragments:

entryViewModel = activity?.run {
        ViewModelProviders.of(this, EntryViewModelFactory(this.application, EntryRepository(this.application))).get(EntryViewModel::class.java)
    } ?: throw Exception("Invalid Activity")

Here's the commit where I made the change: https://github.com/randroid88/TodayILearned/commit/e307bd3f238e68a399a2a1619438770d908a606d

Should I share my ViewModel across two fragments?

1 Answers1