Fix #33

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## 3.0.1
 
-- fix: docs not loading after the first sroll
+- fix: docs not loading after the first scroll
 
 ## 3.0.0
 

lib/src/realtime_db_pagination.dart

@@ -45,6 +45,7 @@ class RealtimeDBPagination extends StatefulWidget {
     required this.itemBuilder,
     required this.orderBy,
     super.key,
+    this.descending = false,
     this.separatorBuilder,
     this.limit = 10,
     this.viewType = ViewType.list,
@@ -69,6 +70,8 @@ class RealtimeDBPagination extends StatefulWidget {
   /// ### Note:
   /// - The query must **NOT** contain a `limitToFirst` or `limitToLast` itself.
   /// - The `limit` must be set using the [limit] property of this widget.
+  /// - The query must **NOT** contain `orderBy` itself. The field to order the
+  /// data by must be set using the [orderBy] property of this widget.
   final Query query;
 
   /// The builder to use to build the items in the list.
@@ -90,6 +93,11 @@ class RealtimeDBPagination extends StatefulWidget {
   /// If null, the data will be sorted by the key.
   final String? orderBy;
 
+  /// Fetches data is decending order for the given [orderBy] field.
+  ///
+  /// Default value is `false`.
+  final bool descending;
+
   /// The builder to use to render the separator.
   ///
   /// Only used if [viewType] is [ViewType.list].
@@ -202,14 +210,37 @@ class _RealtimeDBPaginationState extends State<RealtimeDBPagination> {
 
     if (getMore) setState(() => _isFetching = true);
 
+    // Sets limit of nodes to fetch.
+    // If currently 15 items are loaded, and limit is 5 then total 20 items
+    // will be fetched including the ones already present.
     final docsLimit = _data.length + (getMore ? widget.limit : 0);
-    var docsQuery = widget.query.limitToFirst(docsLimit);
+    var docsQuery = widget.descending
+        ? widget.query.limitToLast(docsLimit)
+        : widget.query.limitToFirst(docsLimit);
+
     if (_data.isNotEmpty) {
-      docsQuery = docsQuery.startAt(
-        Map<String, dynamic>.from(
-          _data.first.value! as Map<Object?, Object?>,
-        )[widget.orderBy],
-      );
+      if (widget.descending) {
+        // Sets ending point from where before data should be fetched.
+        // If currently 15 items are loaded, and limit is 5 then total 20 items
+        // will be fetched where below mentioned value will be the largest and
+        // last in the fetched array (But first in callback array as using
+        // reversed in build method)
+        docsQuery = docsQuery.endAt(
+          Map<String, dynamic>.from(
+            _data.last.value! as Map<Object?, Object?>,
+          )[widget.orderBy],
+        );
+      } else {
+        // Sets starting point from where after data should be fetched.
+        // If currently 15 items are loaded, and limit is 5 then total 20 items
+        // will be fetched where below mentioned value will be the smallest and
+        // first in array
+        docsQuery = docsQuery.startAt(
+          Map<String, dynamic>.from(
+            _data.first.value! as Map<Object?, Object?>,
+          )[widget.orderBy],
+        );
+      }
     }
 
     _streamSub = docsQuery.onValue.listen((DatabaseEvent snapshot) async {
@@ -260,21 +291,39 @@ class _RealtimeDBPaginationState extends State<RealtimeDBPagination> {
     // To cancel previous live listener when new one is set.
     final tempSub = _liveStreamSub;
 
-    var latestDocQuery = widget.query.limitToFirst(1);
+    var latestDocQuery = widget.descending
+        ? widget.query.limitToLast(1)
+        : widget.query.limitToFirst(1);
+
     if (_data.isNotEmpty) {
-      latestDocQuery = latestDocQuery.endBefore(
-        Map<String, dynamic>.from(
-          _data.first.value! as Map<Object?, Object?>,
-        )[widget.orderBy],
-      );
+      if (widget.descending) {
+        // Sets query to fetch data after the last element in the array,
+        // which is the largest value.
+        latestDocQuery = latestDocQuery.startAfter(
+          Map<String, dynamic>.from(
+            _data.last.value! as Map<Object?, Object?>,
+          )[widget.orderBy],
+        );
+      } else {
+        // Sets query to fetch data before the first element in the array,
+        // whch is the smallest value
+        latestDocQuery = latestDocQuery.endBefore(
+          Map<String, dynamic>.from(
+            _data.first.value! as Map<Object?, Object?>,
+          )[widget.orderBy],
+        );
+      }
     }
 
     _liveStreamSub = latestDocQuery.onValue.listen(
       (DatabaseEvent snapshot) async {
         await tempSub?.cancel();
         if (snapshot.snapshot.children.isEmpty) return;
 
-        _data.insert(0, snapshot.snapshot.children.first);
+        _data.insert(
+          widget.descending ? _data.length : 0,
+          snapshot.snapshot.children.first,
+        );
 
         // To handle newly added data after this curently loaded data.
         await _setLiveListener();
@@ -319,7 +368,7 @@ class _RealtimeDBPaginationState extends State<RealtimeDBPagination> {
         : _data.isEmpty
             ? widget.onEmpty
             : BuildPagination(
-                items: _data,
+                items: widget.descending ? _data.reversed.toList() : _data,
                 itemBuilder: widget.itemBuilder,
                 separatorBuilder: widget.separatorBuilder ?? separatorBuilder,
                 isLoading: _isFetching,