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I've been searching on this topic for a while now, without any success. Since the last update of Navigation Component 2.5.0 in combination with BottomNavigationView the nav controller retain the stack state for each tab of BottomNavView.

Now, I am asking if there is any way to exclude a graph or some fragments from this rule ?

More in details:

  • I have 1 activity and the rest are fragments
  • I have BottomNavigationView with 4 tabs
  • it is setup with nav controller
  • each tab starts a separate graph (no confusions) - seems clean, especially in a bigger application
  • besides this, I have 2 icons on the toolbar (let's say help and settings)
  • these two icons, are Global Actions because are started from activity, not from a fragment, and can be accessed from almost any point

Why do I want to exclude some fragments (help and settings) from this rule to retain their state? Well, because navigating to one of them and then changing the BottomNavigationView tabs back and forth, I can end up having these fragments over all of my 4 tabs (or those 4 main graphs)

What I have tried?

  1. A tricky solution to add settings and faq into the BottomNavigationView but without being visible, and just link the global action to that tab (manually setting the current item of the BottomNavView) - failed, because I've ended up with 6 items in the BNV and it will cause a crash, as more than 5 items is a design concern.
  2. I tried using two controllers for this activity, 1 to be linked with BNV and the other to take care of the global actions, of course I ended up with a bit of a mess.

Maybe I am asking too much from Android, but I would like to be able to keep this default behaviour added in 2.5.0 for Navigation but at the same time write some exceptions from it. I wouldn't mind manually handling the navigations for each BNV tabs, but my issue is with the global actions.

Any suggestions would be highly appreciated.

Ionut J. Bejan
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1 Answers1

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Now, I am asking if there is any way to exclude a graph or some fragments from this rule ?

You can exclude the entirety of the NavigationBarView from the state preservation by using an overload of setupWithNavController with saveState set to false. However, you cannot exclude certain fragments/routes as you like. It's either all or none, as far as NavigationUI is concerned.

As I see it, you have three viable options:

  • Locally modify the NavigationUI source to implement exclusions
  • Using nested NavHostFragments, as in your 2nd attempt
  • Prevent the user from navigating to another tab while help or settings fragments are active (hide the BNV with NavController#addOnDestinationChangedListener?)

I'd say the second option is by far the ideal one here, as it is also what actually makes sense hierarchically from the way you've defined your app behavior: The global actions need not be coupled to your BNV tabs.

This answer nicely demonstrates how you would obtain the NavController references. It is actually not too bad to work with once you've gotten a grasp of what NavController needs to be doing what. In fact, it's arguably the least hacky design you could go for.

Ved
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