Clear BottomNavigation item stack before navigate away

ExtendedBottomNavigationView.kt

// first i extends BottomNavigationView class so it can attach multiple "setOnNavigationItemSelectedListener"

class ExtendedBottomNavigationView(
        context     : Context,
        attrs       : AttributeSet?= null,
        defStyleAttr: Int = 0
    ) : BottomNavigationView(context, attrs, defStyleAttr) {

    constructor (context : Context) : this(context, null, 0)

    constructor (context : Context, attrs : AttributeSet) : this(context, attrs, 0)

    private val selectedListeners = mutableListOf<(menuItem : MenuItem) -> Boolean>()

    fun addOnNavigationItemSelectedListener(listener: (menuItem : MenuItem) -> Boolean) {
        this.selectedListeners.add(listener)
        this.setOnNavigationItemSelectedListener {
            var result = false
            for (i in 0 until this.selectedListeners.size) {
                result = this.selectedListeners[i].invoke(it)
                if (result) {
                    continue
                } else {
                    break
                }
            }
            result
        }
    }
}

NavigationExtension.kt

// modify google samples NavigationExtension.kt extension function to use our class

fun ExtendedBottomNavigationView.setupWithNavController(
    navGraphIds     : List<Int>,
    fragmentManager : FragmentManager,
    containerId     : Int,
    intent          : Intent
): LiveData<NavController> {
	...
	
  // replace "setOnNavigationItemSelectedListener" to use this
	addOnNavigationItemSelectedListener { item ->
		...
	}
	
	...
}
 

YourActivity.kt

// in your activity
private fun setupBottomNavigationBar() {
	val navGraphIds = listOf(
            ...,
            ...,
            ...,
            ...,
            ...)
            
	// attach listener to your bottom tab nav view
	this.extended_bottom_navigation_view?.addOnNavigationItemSelectedListener {
		// must return boolean, true to proceed tab changes, or false to halt it
		// depends on your app behaviour, you may want to exclude some tabs
		when (it.itemId) {
			... -> {
				true
			}
			else -> {
				this.clearBackStackBeforeMoveTab(it)
			}
		}
	}
 }
 
 private fun clearBackStackBeforeMoveTab(it: MenuItem): Boolean {
	// must return boolean, true to proceed tab changes, or false to halt it
	
	// try various methods to clean backstack, or set the startDestination / destination to root
	return if (willBeAbleToBackStack == null) {
		try {
			this.currentNavController?.value?.navigate(it.itemId, null,
				NavOptions.Builder().setPopUpTo(it.itemId, true).build())
			true
		} catch (e: Exception) {
			e.printStackTrace()
			true
		}
	} else {
		if (it.itemId == this.currentNavController?.value?.graph?.id) {
			try {
				this.currentNavController?.value?.navigate(this.currentNavController?.value?.graph?.startDestination?: 0, null,
					NavOptions.Builder().setPopUpTo(it.itemId, true).build())
				val newPosition = this.activity_post_auth__bottom_navigation_view?.postionForItem(it)
				if (newPosition != null) this.activity_post_auth__bottom_navigation_view?.checkItem(newPosition)
				true
			} catch (e: Exception) {
				e.printStackTrace()
				true
			}
		} else {
			this.currentNavController?.value?.navigateUp() != true
			true
		}
	}
}