Fragments destroyed / recreated with Jetpack's Android Navigation components

Ian Lake from google replied me that we can store the view in a variable and instead of inflating a new layout, just return the instance of pre-stored view on onCreateView()

Source: https://twitter.com/ianhlake/status/1103522856535638016

Leakcanary may show this as leak but its false positive..

You can have a persistent view for your fragment through below implementation

BaseFragment

open class BaseFragment : Fragment(){

        var hasInitializedRootView = false
        private var rootView: View? = null

        fun getPersistentView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?, layout: Int): View? {
            if (rootView == null) {
                // Inflate the layout for this fragment
                rootView = inflater?.inflate(layout,container,false)
            } else {
                // Do not inflate the layout again.
                // The returned View of onCreateView will be added into the fragment.
                // However it is not allowed to be added twice even if the parent is same.
                // So we must remove rootView from the existing parent view group
                // (it will be added back).
                (rootView?.getParent() as? ViewGroup)?.removeView(rootView)
            }

            return rootView
        }
    }

MainFragment

class MainFragment : BaseFragment() {


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return getPersistentView(inflater, container, savedInstanceState, R.layout.content_main)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        if (!hasInitializedRootView) {
            hasInitializedRootView = true
            setListeners()
            loadViews()
        }
    }
}

Source

I tried like this, and it works for me.

• Init ViewModel by navGraphViewModels (Live on Navigation scope)
• Store any to-restore state in ViewModel

// fragment.kt
private val vm by navGraphViewModels<VM>(R.id.nav_graph) { vmFactory }

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    // Restore state
    vm.state?.let {
        (recycler.layoutManager as GridLayoutManager).onRestoreInstanceState(it)
    }
}

override fun onPause() {
    super.onPause()
    // Store state
    vm.state = (recycler.layoutManager as GridLayoutManager).onSaveInstanceState()
}

// vm.kt
var state:Parcelable? = null