Bottom space bar: always try to center the selected space

Change-Id: Ia9820869d27b409da50900ab9819cec9e5e4691b

vector/src/main/java/im/vector/app/features/home/HomeDetailFragment.kt

@@ -171,10 +171,10 @@ class HomeDetailFragment :
 
         checkNotificationTabStatus()
 
+        views.spaceBarRecyclerView.layoutManager = LinearLayoutManager(context)
         val spaceBarAdapter = spaceBarController.also { controller ->
             controller.spaceRoomListener = spaceBarListener
         }.adapter
-        views.spaceBarRecyclerView.layoutManager = LinearLayoutManager(context)
         views.spaceBarRecyclerView.adapter = spaceBarAdapter
 
         // Reduce sensitivity of viewpager to avoid scrolling horizontally by accident too easily

vector/src/main/java/im/vector/app/features/home/room/list/home/spacebar/SpaceBarController.kt

@@ -69,8 +69,10 @@ class SpaceBarController @Inject constructor(
             )
             onBind { _, view, _ ->
                 host.carousel = view
+                view.post {
                     host.scrollToSpace(selectedSpace?.roomId)
                 }
+            }
 
             onUnbind { _, _ ->
                 host.carousel = null
@@ -137,12 +139,17 @@ class SpaceBarController @Inject constructor(
         var effectivePosition = position
         val lm = safeCarousel.layoutManager as? LinearLayoutManager
         if (lm != null) {
-            // Look-ahead of 1
-            if (lm.findFirstCompletelyVisibleItemPosition() >= position) {
-                effectivePosition--
-            } else if (lm.findLastVisibleItemPosition() <= position) {
-                effectivePosition++
+            // Scroll to an element such that the new selection is roughly in the middle
+            val firstVisible = lm.findFirstCompletelyVisibleItemPosition()
+            val visibleRange = lm.findLastCompletelyVisibleItemPosition() - firstVisible + 1
+            val overshoot = visibleRange/2
+            val currentMiddle = firstVisible + overshoot
+            if (currentMiddle < position) {
+                effectivePosition = position + overshoot
+            } else if (currentMiddle > position) {
+                effectivePosition = position - overshoot
             }
+            // List limits
             effectivePosition = max(0, min(effectivePosition, lm.itemCount-1))
         }
         safeCarousel.smoothScrollToPosition(effectivePosition)