Optimize lazy column

features/messages/src/main/java/io/element/android/x/features/messages/MessagesScreen.kt

@@ -10,7 +10,7 @@ import androidx.compose.foundation.interaction.MutableInteractionSource
 import androidx.compose.foundation.layout.*
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyListState
-import androidx.compose.foundation.lazy.itemsIndexed
+import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.ExperimentalMaterialApi
@@ -230,7 +230,11 @@ fun TimelineItems(
         verticalArrangement = Arrangement.Bottom,
         reverseLayout = true
     ) {
-        itemsIndexed(timelineItems) { index, timelineItem ->
+        items(
+            items = timelineItems,
+            contentType = { timelineItem -> timelineItem.contentType() },
+            key = { timelineItem -> timelineItem.key() },
+        ) { timelineItem ->
             TimelineItemRow(
                 timelineItem = timelineItem,
                 onClick = onClick,
@@ -245,6 +249,20 @@ fun TimelineItems(
     }
 }
 
+private fun MessagesTimelineItemState.key(): String {
+    return when (this) {
+        is MessagesTimelineItemState.MessageEvent -> id
+        is MessagesTimelineItemState.Virtual -> id
+    }
+}
+
+private fun MessagesTimelineItemState.contentType(): Int {
+    return when (this) {
+        is MessagesTimelineItemState.MessageEvent -> 0
+        is MessagesTimelineItemState.Virtual -> 1
+    }
+}
+
 
 @Composable
 fun TimelineItemRow(

features/roomlist/src/main/java/io/element/android/x/features/roomlist/RoomListScreen.kt

@@ -122,7 +122,11 @@ fun RoomListContent(
                         .nestedScroll(nestedScrollConnection),
                     state = lazyListState,
                 ) {
-                    items(roomSummaries) { room ->
+                    items(
+                        items = roomSummaries,
+                        contentType = { room -> room.contentType() },
+                        key = { room -> room.key() },
+                    ) { room ->
                         RoomSummaryRow(room = room, onClick = ::onRoomClicked)
                     }
                 }
@@ -134,6 +138,9 @@ fun RoomListContent(
     }
 }
 
+private fun RoomListRoomSummary.key() = id
+private fun RoomListRoomSummary.contentType() = isPlaceholder
+
 private fun LazyListState.isScrolled(): Boolean {
     return firstVisibleItemIndex > 0 || firstVisibleItemScrollOffset > 0
 }