CODEWITHSUNDEEP
androidkotlin
test
test

Reputation: 467

kotlin android nav graph go back causes recreate a old fragment

I Have huge probleme in my project when I go back from fragment B to fragment A just like this :

findNavController().navigateUp()

or

activity?.onBackPressed()

causes that a old fragment is recreated And I do not why

this is my action:

<action
            android:id="@+id/action_fragmentA_to_fragmentB"
            app:destination="@id/fragmentB" />






 val action = ScanningFragmentDirections.action_fragmentA_to_fragmentB(
            scanningViewModel.containerLevel,
            container
        )
        NavHostFragment.findNavController(this).navigate(action)



override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
     binding =
        DataBindingUtil.inflate(inflater, R.layout.scanning_fragment, container, false)
    binding!!.viewmodel = scanningViewModel
    binding!!.lifecycleOwner = this
    return binding!!.root
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    init()
}

Upvotes: 1

Views: 3153

Answers (2)

Xid
Xid

Reputation: 4951

When you navigate from one fragment to another your fragment view is destroyed(onDestroyView is called). When you navigate back to a fragment you previously were in the view is recreated (onCreateView is called).

There may be scenarios wherein you do not want your fragment to be recreated (Some time ago I had a fragment with a MapView and I didn't want to have to add all the different markers and polygons again). You can try something like this:

Create a field in your fragment class to save your view:

private lateinit var contentView: View

In the onCreateView function only inflate the view if your variable has not been intialised.

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    if (!::contentView.isInitialized) {
        contentView = inflater.inflate(R.layout.fragment_home, container, false)
    } 

    return contentView
}

Upvotes: 4

i30mb1
i30mb1

Reputation: 4776

When you calling findNavController().navigate(...) under the hood system calling :

FragmentTransaction ft = mFragmentManager.beginTransaction();
ft.replace(mContainerId, frag);

That mean that your fragment will be fully destroyed and recreate again when you return to him via backstack.

Upvotes: 0

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