Fix scroll-to-bottom jumping back to initial event

Change-Id: I4d5ad6e2b2c2e47d79f5da2fd596de69a04c687a

matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/session/room/timeline/Timeline.kt

@@ -59,22 +59,22 @@ interface Timeline {
     /**
      * Event that should be displayed first, before the user scrolls.
      */
-    fun getInitialEventId(): String?
+    fun getTargetEventId(): String?
 
     /**
-     * Change initial event id
+     * The event id we want to display first when showing the timeline
      */
-    fun setInitialEventId(eventId: String?)
+    fun setTargetEventId(eventId: String?)
 
     /**
-     * Offset for the initial event, e.g. if we want to load the event just below said id
+     * Offset for the target event, e.g. if we want to load the event just below said id
      */
-    fun getInitialEventIdOffset(): Int
+    fun getTargetEventOffset(): Int
 
     /**
-     * Set the offset for the initial event, e.g. if we want to load the event just below said id
+     * Set the offset for the target event, e.g. if we want to load the event just below said id
      */
-    fun setInitialEventIdOffset(offset: Int)
+    fun getTargetEventOffset(offset: Int)
 
     /**
      * Check if the timeline can be enriched by paginating.

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/timeline/DefaultTimeline.kt

@@ -53,7 +53,7 @@ import java.util.concurrent.atomic.AtomicReference
 
 internal class DefaultTimeline(private val roomId: String,
                                private val initialEventId: String?,
-                               private var initialEventIdOffset: Int = 0,
+                               private var targetEventOffset: Int = 0,
                                private val realmConfiguration: RealmConfiguration,
                                private val loadRoomMembersTask: LoadRoomMembersTask,
                                private val readReceiptHandler: ReadReceiptHandler,
@@ -88,6 +88,7 @@ internal class DefaultTimeline(private val roomId: String,
     private var isFromThreadTimeline = false
     private var rootThreadEventId: String? = null
 
+    private var targetEventId = initialEventId
     private val dimber = Dimber("TimelineChunks", DbgUtil.DBG_TIMELINE_CHUNKS)
 
     private val strategyDependencies = LoadTimelineStrategy.Dependencies(
@@ -252,6 +253,8 @@ internal class DefaultTimeline(private val roomId: String,
         }
         strategy.onStop()
 
+        setTargetEventId(eventId)
+
         strategy = when {
             rootThreadEventId != null -> buildStrategy(LoadTimelineStrategy.Mode.Thread(rootThreadEventId))
             eventId == null           -> buildStrategy(LoadTimelineStrategy.Mode.Live)
@@ -393,21 +396,20 @@ internal class DefaultTimeline(private val roomId: String,
                 }
     }
 
-    override fun getInitialEventId(): String? {
-        return initialEventId
+    override fun getTargetEventId(): String? {
+        return targetEventId
     }
 
-    override fun setInitialEventId(eventId: String?) {
-        // SC-TODO?? -- just changing initialEventId to var is not enough, we get duplicated timelines :O
-        //initialEventId = eventId
+    override fun setTargetEventId(eventId: String?) {
+        targetEventId = eventId
     }
 
-    override fun getInitialEventIdOffset(): Int {
-        return initialEventIdOffset
+    override fun getTargetEventOffset(): Int {
+        return targetEventOffset
     }
 
-    override fun setInitialEventIdOffset(offset: Int) {
-        initialEventIdOffset = offset
+    override fun getTargetEventOffset(offset: Int) {
+        targetEventOffset = offset
     }
 }
 

vector/src/main/java/im/vector/app/features/home/room/detail/ScrollOnNewMessageCallback.kt

@@ -65,8 +65,8 @@ class ScrollOnNewMessageCallback(private val layoutManager: BetterLinearLayoutMa
             var scrollToEvent = initialForceScrollEventId
             var scrollOffset = 0
             if (initialForceScrollEventId == null) {
-                scrollToEvent = timelineEventController.timeline?.getInitialEventId()
-                scrollOffset = timelineEventController.timeline?.getInitialEventIdOffset() ?: 0
+                scrollToEvent = timelineEventController.timeline?.getTargetEventId()
+                scrollOffset = timelineEventController.timeline?.getTargetEventOffset() ?: 0
             }
             if (scrollToEvent == null) {
                 layoutManager.scrollToPositionWithOffset(0, 0)

vector/src/main/java/im/vector/app/features/home/room/detail/TimelineFragment.kt

@@ -959,7 +959,7 @@ class TimelineFragment @Inject constructor(
             scrollOnNewMessageCallback.forceScrollOnNextUpdate()
             timelineViewModel.timeline.restartWithEventId(null)
         } else {
-            timelineViewModel.timeline.setInitialEventId(null)
+            timelineViewModel.timeline.setTargetEventId(null)
             layoutManager.scrollToPositionWithOffset(0, 0)
         }
     }

vector/src/main/java/im/vector/app/features/home/room/detail/TimelineViewModel.kt

@@ -141,7 +141,7 @@ class TimelineViewModel @AssistedInject constructor(
     val timeline = timelineFactory.createTimeline(viewModelScope, room, eventId, initialState.rootThreadEventId).apply {
         // Target the event just below $eventId in case that it is the readMarkerId
         if (initialState.eventId == null && eventId != null) {
-            setInitialEventIdOffset(-1)
+            getTargetEventOffset(-1)
         }
     }