Bloqueo de la aplicación después de que la actividad haya muerto en segundo plano

Tengo un problema con una aplicación que usa ViewPager para mostrar fragmentos. Todo funciona bien hasta que la aplicación pasa a segundo plano y se mata desde el sistema operativo. Parece que después de la restauración tengo 2 IncidentScreenFragment que controlan los eventos, uno con un presentador nulo (MVP) que bloquea mi aplicación.

My HomeActivity se ve así:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
        presenter.onViewCreated()
        initViews(savedInstanceState)
    }

    private fun initViews(savedInstanceState: Bundle?){
        mapView.onCreate(savedInstanceState)
        mapView.getMapAsync(this)
        initFragment()
        initMenu()
    }
    private fun initFragment(){
        homeFragment = HomeScreenFragment.newInstance()
        incidentFragment = IncidentScreenFragment.newInstance()
        chatFragment = ChatFragment.newInstance()
        weatherFragment = WeatherFragment.newInstance()

        viewPager.adapter = ViewPagerAdapter(supportFragmentManager, this)
        viewPager.offscreenPageLimit = 4

        viewPager?.addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
            override fun onPageScrollStateChanged(state: Int) {}
            override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {}
            override fun onPageSelected(position: Int) {bottom_navigation.currentItem = position}
        })
    }

    override fun getFragmentByPos(pos: Int): Fragment {
        return when(pos){
            0 -> homeFragment
            1 -> incidentFragment
            2 -> chatFragment
            3 -> weatherFragment
            else -> {
                homeFragment
            }
        }
    }

Y mi adaptador:

class ViewPagerAdapter internal constructor(fm: FragmentManager, activity:infinite_software.intelligence_center.intelligencecenter.ui.home.FragmentManager) : FragmentPagerAdapter(fm) {

    private val COUNT = 4
    private val activity = activity

    override fun getItem(position: Int): Fragment{
        var fragment: Fragment? = null
        when (position) {
            0 -> fragment = activity.getFragmentByPos(0)
            1 -> fragment = activity.getFragmentByPos(1)
            2 -> fragment = activity.getFragmentByPos(2)
            3 -> fragment = activity.getFragmentByPos(3)
        }

        return fragment!!
    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        super.destroyItem(container, position, `object`)
    }

    override fun getCount(): Int {
        return COUNT
    }

    override fun getPageTitle(position: Int): CharSequence? {
        return "Section " + (position + 1)
    }
}

Cada fragmento tiene un método estático que devuelve un nuevo fragmento:

    companion object {
        fun newInstance(): HomeScreenFragment {
            return HomeScreenFragment()
        }
    }

Cuando la aplicación ha sido eliminada en segundo plano, me doy cuenta de que hay 2 objetos (Fragmento) que escuchan el evento, uno con El presentador instancia correctamente y otro sin él.

Debajo de mi clase abstracta BaseFragment:

abstract class BaseFragment<P : BasePresenter<BaseView>> : BaseView,Fragment() {
    protected lateinit var presenter: P

    override fun getContext(): Context {
        return activity as Context
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return super.onCreateView(inflater, container, savedInstanceState)
    }

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

    override fun showError(error: String) {
        (activity as BaseActivity<BasePresenter<BaseView>>).showError(error)
    }

    override fun showError(errorResId: Int) {
        (activity as BaseActivity<BasePresenter<BaseView>>).showError(errorResId)
    }

    abstract fun onBackPressed(): Boolean

    /**
     * Instantiates the presenter the Fragment is based on.
     */
    protected abstract fun instantiatePresenter(): P
    abstract val TAG: String

Código de fragmento de incidente:

class IncidentScreenFragment: BaseFragment<IncidentScreenPresenter>(), BaseView, IncidentView, AlertFilterListener, AlertItemClickListener, IncidentDetailListener {

    var rvAdapter : IncidentAdapter? = null

    var state : Int = LIST_STATE

    override fun instantiatePresenter(): IncidentScreenPresenter {
        return IncidentScreenPresenter(this)
    }

    override val TAG: String
        get() = "INCIDENT"

    override fun getContext(): Context {
        return activity as Context
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        return inflater.inflate(R.layout.fragment_incident, container, false)
    }

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

    private fun initViews(){
        //Reclycler view
        alertRV.layoutManager = LinearLayoutManager(context)
        rvAdapter = IncidentAdapter(ArrayList(), context, this)
        alertRV.adapter = rvAdapter

        //Apply Listeners
        headerBox.setFilterListener(this)
        incidentDetailView.setListener(this)
    }

    override fun initObserve() {
        //Init observe presenter model
        val alertObserver = Observer<ArrayList<AlertModel>> { alerts ->
            Timber.d("Data received from Presenter [$alerts]")
            showAlertList(alerts)
        }
        presenter.filteredAlertList.observe(context as BaseActivity<BasePresenter<BaseView>>,alertObserver)
    }

    override fun updateThisFilters(boxState: Boolean, level: Int) {
        presenter.updateFilterList(boxState,level)
    }

    fun showOnlyThisLevel(level:Int){
        presenter.showOnlyThisLevel(level)
        headerBox.disableBoxExcept(level)
    }

    fun showAlertList(list: ArrayList<AlertModel>){
        rvAdapter?.updateData(list)
    }

    override fun onItemClick(model: AlertModel) {
        presenter.loadAlertDetail(model)
    }

    override fun showAlertDetail(model: AlertModel) {
        incidentDetailView.setUpFromModel(model)
        WhiteWizard.slideLeftEffect(incidentDetailView,incidentListRootElement)
        state = DETAIL_STATE
    }

    override fun onbackFromDetailPressed() {
        WhiteWizard.slideRightEffect(incidentListRootElement,incidentDetailView)
        state = LIST_STATE
    }

    override fun showLoader() {
        loaderIncident.visibility = View.VISIBLE
    }

    override fun hideLoader() {
        loaderIncident.visibility = View.INVISIBLE
    }

    override fun onBackPressed(): Boolean {
        when(state){
            LIST_STATE -> return false
            DETAIL_STATE -> {
                onbackFromDetailPressed()
                return true
            }
            else -> return false
        }
    }

    fun newInstance(): IncidentScreenFragment {
            return  IncidentScreenFragment()
    }

}

Cuando hago clic en el botón en homePage para mostrar el contenido del fragmento, obtuve:

 Process: XXXXXX, PID: 3192
    kotlin.UninitializedPropertyAccessException: lateinit property presenter has not been initialized
        at infinite_software.intelligence_center.intelligencecenter.base.BaseFragment.getPresenter(BaseFragment.kt:11)
        at XXXXXX.ui.home.incidentScreen.IncidentScreenFragment.showOnlyThisLevel(IncidentScreenFragment.kt:78)
        at XXXXXX.ui.home.HomeActivity.filterDataWithSeverity(HomeActivity.kt:110)
        at XXXXXX.ui.home.homeScreen.HomeScreenFragment.filterBy(HomeScreenFragment.kt:76)
        at XXXXXX.ui.home.homeScreen.HomeScreenFragment$initViews$5.onClick(HomeScreenFragment.kt:56)

Si intento imprimir el identificador de Fragment, obtengo 2 identificadores diferentes de la llamada al método showOnlyThisLevel() y onBackPressed(). ¿Qué echo de menos?

Solución

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    setContentView(R.layout.activity_main)
    ...
    homeFragment = HomeScreenFragment.newInstance()
    incidentFragment = IncidentScreenFragment.newInstance()
}

override fun getItem(position: Int): Fragment = when(position) {
     ...
     1 -> activity.incidentFragment
     ...
}

    // Do we already have this fragment?
    String name = makeFragmentName(container.getId(), itemId);
    Fragment fragment = mFragmentManager.findFragmentByTag(name);
    if (fragment != null) {
        if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
        mCurTransaction.attach(fragment);
    } else {
        fragment = getItem(position);
        if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
        mCurTransaction.add(container.getId(), fragment,
                makeFragmentName(container.getId(), itemId));

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