Notification tab cleanups (#3692)

- Use NO_POSITION instead of hardcoding 0.
- Don't set a state restoration policy, PagingDataAdapter already does that
- Return the closest item, not just the closest page, in getRefreshKey

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationsFragment.kt

@@ -41,6 +41,7 @@ import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.DividerItemDecoration
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import androidx.recyclerview.widget.RecyclerView.NO_POSITION
 import androidx.recyclerview.widget.RecyclerView.SCROLL_STATE_IDLE
 import androidx.recyclerview.widget.SimpleItemAnimator
 import androidx.swiperefreshlayout.widget.SwipeRefreshLayout.OnRefreshListener
@@ -201,7 +202,7 @@ class NotificationsFragment :
 
                 // Save the ID of the first notification visible in the list, so the user's
                 // reading position is always restorable.
-                layoutManager.findFirstVisibleItemPosition().takeIf { it >= 0 }?.let { position ->
+                layoutManager.findFirstVisibleItemPosition().takeIf { it != NO_POSITION }?.let { position ->
                     adapter.snapshot().getOrNull(position)?.id?.let { id ->
                         viewModel.accept(InfallibleUiAction.SaveVisibleId(visibleId = id))
                     }

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationsPagingAdapter.kt

@@ -117,10 +117,6 @@ class NotificationsPagingAdapter(
         )
     }
 
-    init {
-        stateRestorationPolicy = StateRestorationPolicy.PREVENT_WHEN_EMPTY
-    }
-
     override fun getItemViewType(position: Int): Int {
         return NotificationViewKind.from(getItem(position)?.type).ordinal
     }

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationsPagingSource.kt

@@ -204,8 +204,9 @@ class NotificationsPagingSource @Inject constructor(
 
     override fun getRefreshKey(state: PagingState<String, Notification>): String? {
         return state.anchorPosition?.let { anchorPosition ->
-            val anchorPage = state.closestPageToPosition(anchorPosition)
-            anchorPage?.prevKey ?: anchorPage?.nextKey
+            val id = state.closestItemToPosition(anchorPosition)?.id
+            Log.d(TAG, "  getRefreshKey returning $id")
+            return id
         }
     }