Stop fragment refresh in bottom nav using navhost

Question

This problem has been asked a few times now, but we are in 2020 now, did anyone find a good usable solution to this yet?

I want to be able to navigate using the bott

Answer 1

If you are using Jetpack, the easiest way to solve this is using ViewModel

You have to save all valuable data and not make unnecessary database loads or network calls everytime you go to a fragment from another.

UI controllers such as activities and fragments are primarily intended to display UI data, react to user actions, or handle operating system communication, such as permission requests.

Here is when we use ViewModels

ViewModel objects are automatically retained during configuration changes so that data they hold is immediately available to the next activity or fragment instance.

So if the fragment is recreated, all your data will be there instantly instead of make another call to database or network. Its important to know that if the activity or fragment that holds the ViewModel is reacreated, you will receive the same ViewModel instance created before.

But in this case you have to specify the ViewModel to have activity scope instead of fragment scope, independently if you are using a shared ViewModel for all the fragments, or a different ViewModel for every fragment.

Here is a little example using LiveData too:

//Using KTX
val model by activityViewModels()
model.getData().observe(viewLifecycleOwner, Observer{ data ->
        // update UI
    })

//Not using KTX
val model by lazy {ViewModelProvider(activity as ViewModelStoreOwner)[MyViewModel::class.java]}
model.getData().observe(viewLifecycleOwner, Observer{ data ->
        // update UI
    })

And that's it! Google is actively working on multiple back stack support for bottom tab Navigation and claim that it'll arrive on Navigation 2.4.0 as said here and on this issue tracker if you want and/or your problem is more related to multiple back stack, you can check out those links

Remember fragments still be recreated, usually you don't change component behavior, instead, you adapt your data to them!

I leave you some useful links:

ViewModel Overview Android Developers

How to communicate between fragments and activities with ViewModels - on Medium

Restoring UI State using ViewModels - on Medium