Fragment re-created on bottom navigation view item selected

Question

Following is my code for bottom navigation view item selected

bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationI         


        

Answer 1

I've improved @Viven's answers and written it with Kotlin. My version instantiates fragment only for the first time, hides/shows. I'm new at Kotlin so tell me if I can improve anything.

We need to hold a id to tag map:

private val fragmentTags = hashMapOf(
        R.id.action_home to "home_fragment",
        R.id.action_profile to "profile_fragment"
)

The listener code:

bottomNavigation.run {
    setOnNavigationItemSelectedListener { menuItem ->
        supportFragmentManager.beginTransaction()
                .let { transaction ->
                    // hide current fragment
                    supportFragmentManager.primaryNavigationFragment?.let {
                        // if selected fragment's tag is same, do nothing.
                        if (it.tag == fragmentTags[menuItem.itemId]) {
                            return@setOnNavigationItemSelectedListener true
                        }

                        transaction.hide(it)
                    }

                    var fragment  = supportFragmentManager.findFragmentByTag(fragmentTags[menuItem.itemId])

                    if (fragment == null) {
                        // instantiate fragment for the first time
                        fragment = when(menuItem.itemId) {
                            R.id.action_home -> HomeFragment()
                            R.id.action_profile -> ProfileFragment()
                            else -> null
                        }?.also {
                            // and add it 
                            transaction.add(R.id.frame, it, fragmentTags[menuItem.itemId])
                        }
                    } else {
                        // if it's found show it 
                        transaction.show(fragment)
                    }


                    transaction
                            .setPrimaryNavigationFragment(fragment)
                            .setReorderingAllowed(true)
                }.commitNowAllowingStateLoss()

        return@setOnNavigationItemSelectedListener true
    }

    //bottomNavigation things
    itemIconTintList = null
    selectedItemId = R.id.action_home
}