youngam

class NavigationActivity : AppCompatActivity() {
    private lateinit var fragmentContainer: ViewGroup
    private lateinit var navigationDelegate: NavigationDelegate


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        fragmentContainer = findViewById(R.id.fragment_container) as ViewGroup
        navigationDelegate = NavigationDelegate(supportFragmentManager, fragmentContainer.id)

youngam

class NavigationDelegate(private val fragmentManager: FragmentManager,
                         private val containerId: Int) {
    
    init {
        fragmentManager.addOnBackStackChangedListener {
            val currentFragment = fragmentManager.findFragmentById(containerId)
            currentFragment.userVisibleHint = true
        }
    }

youngam

override fun setUserVisibleHint(isVisibleToUser: Boolean) {
   isVisibleToUser = isVisibleToUser
   awaitingRunnable?.let {awaitingRunnable.run()}
 }

youngam

public fun initBackStackListener() {
   supportFragmentManager.addOnBackStackChangedListener {
   val currentFragment = supportFragmentManager.findFragmentById(fragmentContainer.id)
   currentFragment.userVisibleHint = true 
}

youngam

public class MasterFragment : Fragment() {  
  public fun navigateToSlave() {
    (activity as MainActivity).navigate(from = this, to = SlaveFragment.newInstance())
  }
}

youngam

class MainActivity : AppCompatActivity() {
    private lateinit var fragmentContainer: ViewGroup


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        fragmentContainer = findViewById(R.id.fragment_container) as ViewGroup
    }

youngam

public class DetectingVisibilityFragment extends Fragment {
      // will talk about this flag later
    private var isVisibleToUser: Boolean = true
    private var awaitingRunnable: Runnable? = null

    // triggered when notification from Server or client EventBus came
    override fun onNotification(newName: String) {
        if(isVisibleToUser) show(newName) 
        else awaitingRunnable = () -> show(newName)
    }

youngam

public class DetectingVisibilityFragment extends Fragment {
      // will talk about this flag later
    private var isVisibleToUser: Boolean = true
    private var awaitingRunnable: Runnable? = null

    // triggered when notification from Server or client EventBus came
    override fun onNotification(newName: String) {
        if(isVisibleToUser) show(newName) 
        else awaitingRunnable = () -> show(newName)
    }