Fix crash reported by the PlayStore.

NullPointerException: at im.vector.riotx.features.home.room.detail.RoomDetailFragment.updateJumpToReadMarkerViewVisibility (RoomDetailFragment.kt:524)
Also properly cleanup model build listener

vector/src/main/java/im/vector/riotx/features/home/room/detail/RoomDetailFragment.kt

@@ -46,6 +46,7 @@ import androidx.recyclerview.widget.RecyclerView
 import butterknife.BindView
 import com.airbnb.epoxy.EpoxyModel
 import com.airbnb.epoxy.EpoxyVisibilityTracker
+import com.airbnb.epoxy.OnModelBuildFinishedListener
 import com.airbnb.mvrx.*
 import com.github.piasy.biv.BigImageViewer
 import com.github.piasy.biv.loader.ImageLoader
@@ -193,6 +194,8 @@ class RoomDetailFragment @Inject constructor(
 
     private lateinit var sharedActionViewModel: MessageSharedActionViewModel
     private lateinit var layoutManager: LinearLayoutManager
+    private lateinit var modelBuildListener: OnModelBuildFinishedListener
+
     private lateinit var attachmentsHelper: AttachmentsHelper
     private lateinit var keyboardStateUtils: KeyboardStateUtils
 
@@ -286,8 +289,9 @@ class RoomDetailFragment @Inject constructor(
     }
 
     override fun onDestroyView() {
-        super.onDestroyView()
+        timelineEventController.removeModelBuildListener(modelBuildListener)
         recyclerView.adapter = null
+        super.onDestroyView()
     }
 
     override fun onDestroy() {
@@ -470,13 +474,14 @@ class RoomDetailFragment @Inject constructor(
         recyclerView.layoutManager = layoutManager
         recyclerView.itemAnimator = null
         recyclerView.setHasFixedSize(true)
-        timelineEventController.addModelBuildListener {
+        modelBuildListener = OnModelBuildFinishedListener {
             it.dispatchTo(stateRestorer)
             it.dispatchTo(scrollOnNewMessageCallback)
             it.dispatchTo(scrollOnHighlightedEventCallback)
             updateJumpToReadMarkerViewVisibility()
             updateJumpToBottomViewVisibility()
         }
+        timelineEventController.addModelBuildListener { modelBuildListener }
         recyclerView.adapter = timelineEventController.adapter
 
         recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
@@ -521,37 +526,41 @@ class RoomDetailFragment @Inject constructor(
         }
     }
 
-    private fun updateJumpToReadMarkerViewVisibility() = jumpToReadMarkerView.post {
-        withState(roomDetailViewModel) {
-            val showJumpToUnreadBanner = when (it.unreadState) {
-                UnreadState.Unknown,
-                UnreadState.HasNoUnread            -> false
-                is UnreadState.ReadMarkerNotLoaded -> true
-                is UnreadState.HasUnread           -> {
-                    if (it.canShowJumpToReadMarker) {
-                        val lastVisibleItem = layoutManager.findLastVisibleItemPosition()
-                        val positionOfReadMarker = timelineEventController.getPositionOfReadMarker()
-                        if (positionOfReadMarker == null) {
-                            false
+    private fun updateJumpToReadMarkerViewVisibility() {
+        jumpToReadMarkerView?.post {
+            withState(roomDetailViewModel) {
+                val showJumpToUnreadBanner = when (it.unreadState) {
+                    UnreadState.Unknown,
+                    UnreadState.HasNoUnread            -> false
+                    is UnreadState.ReadMarkerNotLoaded -> true
+                    is UnreadState.HasUnread           -> {
+                        if (it.canShowJumpToReadMarker) {
+                            val lastVisibleItem = layoutManager.findLastVisibleItemPosition()
+                            val positionOfReadMarker = timelineEventController.getPositionOfReadMarker()
+                            if (positionOfReadMarker == null) {
+                                false
+                            } else {
+                                positionOfReadMarker > lastVisibleItem
+                            }
                         } else {
-                            positionOfReadMarker > lastVisibleItem
+                            false
                         }
-                    } else {
-                        false
                     }
                 }
+                jumpToReadMarkerView.isVisible = showJumpToUnreadBanner
             }
-            jumpToReadMarkerView.isVisible = showJumpToUnreadBanner
         }
     }
 
     private fun updateJumpToBottomViewVisibility() {
         debouncer.debounce("jump_to_bottom_visibility", 250, Runnable {
-            Timber.v("First visible: ${layoutManager.findFirstCompletelyVisibleItemPosition()}")
-            if (layoutManager.findFirstVisibleItemPosition() != 0) {
-                jumpToBottomView.show()
-            } else {
-                jumpToBottomView.hide()
+            if (isAdded) {
+                Timber.v("First visible: ${layoutManager.findFirstCompletelyVisibleItemPosition()}")
+                if (layoutManager.findFirstVisibleItemPosition() != 0) {
+                    jumpToBottomView.show()
+                } else {
+                    jumpToBottomView.hide()
+                }
             }
         })
     }

vector/src/main/java/im/vector/riotx/features/home/room/list/RoomListFragment.kt

@@ -26,6 +26,7 @@ import androidx.core.content.ContextCompat
 import androidx.core.view.isVisible
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import com.airbnb.epoxy.OnModelBuildFinishedListener
 import com.airbnb.mvrx.*
 import com.google.android.material.snackbar.Snackbar
 import im.vector.matrix.android.api.failure.Failure
@@ -38,10 +39,9 @@ import im.vector.riotx.core.error.ErrorFormatter
 import im.vector.riotx.core.platform.OnBackPressed
 import im.vector.riotx.core.platform.StateView
 import im.vector.riotx.core.platform.VectorBaseFragment
-
 import im.vector.riotx.features.home.RoomListDisplayMode
-import im.vector.riotx.features.home.room.list.actions.RoomListQuickActionsSharedAction
 import im.vector.riotx.features.home.room.list.actions.RoomListQuickActionsBottomSheet
+import im.vector.riotx.features.home.room.list.actions.RoomListQuickActionsSharedAction
 import im.vector.riotx.features.home.room.list.actions.RoomListQuickActionsSharedActionViewModel
 import im.vector.riotx.features.home.room.list.widget.FabMenuView
 import im.vector.riotx.features.notifications.NotificationDrawerManager
@@ -65,6 +65,7 @@ class RoomListFragment @Inject constructor(
 
 ) : VectorBaseFragment(), RoomSummaryController.Listener, OnBackPressed, FabMenuView.Listener {
 
+    private lateinit var modelBuildListener: OnModelBuildFinishedListener
     private lateinit var sharedActionViewModel: RoomListQuickActionsSharedActionViewModel
     private val roomListParams: RoomListParams by args()
     private val roomListViewModel: RoomListViewModel by fragmentViewModel()
@@ -118,8 +119,9 @@ class RoomListFragment @Inject constructor(
     }
 
     override fun onDestroyView() {
-        super.onDestroyView()
+        roomController.removeModelBuildListener(modelBuildListener)
         roomListView.adapter = null
+        super.onDestroyView()
     }
 
     private fun openSelectedRoom(event: RoomListViewEvents.SelectRoom) {
@@ -198,7 +200,8 @@ class RoomListFragment @Inject constructor(
         roomListView.layoutManager = layoutManager
         roomListView.itemAnimator = RoomListAnimator()
         roomController.listener = this
-        roomController.addModelBuildListener { it.dispatchTo(stateRestorer) }
+        modelBuildListener = OnModelBuildFinishedListener { it.dispatchTo(stateRestorer) }
+        roomController.addModelBuildListener(modelBuildListener)
         roomListView.adapter = roomController.adapter
         stateView.contentView = roomListView
     }