fix: fix big prefetch index not working for prepending (#12)

* fix: fix prepend load when `prefetchIndex` is far from the items visible on the screen. Signed-off-by: Sahil Kumar <xdsahil@gmail.com> * chore: update CHANGELOG.md Signed-off-by: Sahil Kumar <xdsahil@gmail.com> --------- Signed-off-by: Sahil Kumar <xdsahil@gmail.com>
xsahil03x · Dec 1, 2024 · 39bb3be · 39bb3be
1 parent 72ab5dc
commit 39bb3be
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Upcoming
 
+- [[#11]](https://github.com/xsahil03x/super_paging/issues/11) Fix generating prepend load trigger notification when `prefetchIndex` is bigger than the items visible on the screen.
 - [[#7](https://github.com/xsahil03x/super_paging/issues/7)] Fix generating load trigger notification when `itemCount` is less than `prefetchIndex`.
 - Added support for the `Pager.refresh` method to accept an optional `refreshKey` parameter.
 

diff --git a/lib/src/page_fetcher.dart b/lib/src/page_fetcher.dart
@@ -94,6 +94,9 @@ class PageFetcher<Key, Value> extends ValueNotifier<PagingState<Key, Value>> {
         log.fine('Initial load cancelled');
       },
       () async {
+        // Skip load if already in a loading state.
+        if (value.getLoadState(LoadType.refresh) case Loading()) return;
+
         // Update load state to loading.
         value = value.setLoading(LoadType.refresh);
 
@@ -145,6 +148,9 @@ class PageFetcher<Key, Value> extends ValueNotifier<PagingState<Key, Value>> {
           'Use doInitialLoad for LoadType == refresh',
         );
 
+        // Skip load if already in a loading state.
+        if (value.getLoadState(loadType) case Loading()) return;
+
         final loadKey = _nextLoadKeyOrNull(loadType);
         if (loadKey == null) return;
 

diff --git a/lib/src/widget/bidirectional_paging_list_view.dart b/lib/src/widget/bidirectional_paging_list_view.dart
@@ -348,34 +348,20 @@ class _BidirectionalPagingListViewState<Key, Value>
                 topPages,
                 reverse: true,
                 onBuildingPrependLoadTriggerItem: () {
-                  final canMakeRequest = prependLoadState.maybeMap(
-                    notLoading: (it) => !it.endOfPaginationReached,
-                    orElse: () => false,
-                  );
-
-                  if (canMakeRequest) {
-                    // Schedules the request for the end of this frame.
-                    WidgetsBinding.instance.addPostFrameCallback((_) {
-                      pager.load(LoadType.prepend);
-                    });
-                  }
+                  // Schedules the request for the end of this frame.
+                  WidgetsBinding.instance.addPostFrameCallback((_) {
+                    pager.load(LoadType.prepend);
+                  });
                 },
                 onBuildingAppendLoadTriggerItem: () {
                   // If the bottom list contain items, we don't need to handle
                   // append here.
                   if (!bottomPages.isListEmpty) return;
 
-                  final canMakeRequest = appendLoadState.maybeMap(
-                    notLoading: (it) => !it.endOfPaginationReached,
-                    orElse: () => false,
-                  );
-
-                  if (canMakeRequest) {
-                    // Schedules the request for the end of this frame.
-                    WidgetsBinding.instance.addPostFrameCallback((_) {
-                      pager.load(LoadType.append);
-                    });
-                  }
+                  // Schedules the request for the end of this frame.
+                  WidgetsBinding.instance.addPostFrameCallback((_) {
+                    pager.load(LoadType.append);
+                  });
                 },
               ),
             ),
@@ -392,30 +378,16 @@ class _BidirectionalPagingListViewState<Key, Value>
                   // prepend here.
                   if (!topPages.isListEmpty) return;
 
-                  final canMakeRequest = prependLoadState.maybeMap(
-                    notLoading: (it) => !it.endOfPaginationReached,
-                    orElse: () => false,
-                  );
-
-                  if (canMakeRequest) {
-                    // Schedules the request for the end of this frame.
-                    WidgetsBinding.instance.addPostFrameCallback((_) {
-                      pager.load(LoadType.prepend);
-                    });
-                  }
+                  // Schedules the request for the end of this frame.
+                  WidgetsBinding.instance.addPostFrameCallback((_) {
+                    pager.load(LoadType.prepend);
+                  });
                 },
                 onBuildingAppendLoadTriggerItem: () {
-                  final canMakeRequest = appendLoadState.maybeMap(
-                    notLoading: (it) => !it.endOfPaginationReached,
-                    orElse: () => false,
-                  );
-
-                  if (canMakeRequest) {
-                    // Schedules the request for the end of this frame.
-                    WidgetsBinding.instance.addPostFrameCallback((_) {
-                      pager.load(LoadType.append);
-                    });
-                  }
+                  // Schedules the request for the end of this frame.
+                  WidgetsBinding.instance.addPostFrameCallback((_) {
+                    pager.load(LoadType.append);
+                  });
                 },
               ),
             ),
@@ -471,24 +443,16 @@ class _BidirectionalPagingListViewState<Key, Value>
       // notifications.
       if (prefetchIndex == null) return;
 
-      // Generate notifications at the beginning and end of the list if the
-      // [itemCount] is less than [prefetchIndex].
-      if (prefetchIndex > itemCount) {
-        if (index == 0) onBuildingPrependLoadTriggerItem?.call();
-        if (index == itemCount - 1) onBuildingAppendLoadTriggerItem?.call();
-        return;
-      }
-
-      // Check if the index corresponds to near the top or bottom of the list
-      // based on the [reverse] flag.
-      final (nearTop, nearBottom) = switch (reverse) {
-        true => (index == itemCount - prefetchIndex, index == prefetchIndex),
-        false => (index == prefetchIndex, index == itemCount - prefetchIndex),
+      // Check if the index is near the edge of the list based on the prefetch
+      // index and the direction of the list.
+      final (shouldPrependItems, shouldAppendItems) = switch (reverse) {
+        true => (index >= itemCount - prefetchIndex, index <= prefetchIndex),
+        false => (index <= prefetchIndex, index >= itemCount - prefetchIndex),
       };
 
       // Generate notifications.
-      if (nearTop) onBuildingPrependLoadTriggerItem?.call();
-      if (nearBottom) onBuildingAppendLoadTriggerItem?.call();
+      if (shouldPrependItems) onBuildingPrependLoadTriggerItem?.call();
+      if (shouldAppendItems) onBuildingAppendLoadTriggerItem?.call();
     }
 
     final separatorBuilder = widget.separatorBuilder;

diff --git a/lib/src/widget/paging_sliver_list.dart b/lib/src/widget/paging_sliver_list.dart
@@ -210,31 +210,11 @@ class _PagingSliverListState<Key, Value>
           SliverList(
             delegate: _createDelegate(
               pages,
-              onBuildingPrependLoadTriggerItem: () {
-                final canMakeRequest = prependLoadState.maybeMap(
-                  notLoading: (it) => !it.endOfPaginationReached,
-                  orElse: () => false,
-                );
-
-                if (canMakeRequest) {
-                  // Schedules the request for the end of this frame.
-                  WidgetsBinding.instance.addPostFrameCallback((_) {
-                    pager.load(LoadType.prepend);
-                  });
-                }
-              },
               onBuildingAppendLoadTriggerItem: () {
-                final canMakeRequest = appendLoadState.maybeMap(
-                  notLoading: (it) => !it.endOfPaginationReached,
-                  orElse: () => false,
-                );
-
-                if (canMakeRequest) {
-                  // Schedules the request for the end of this frame.
-                  WidgetsBinding.instance.addPostFrameCallback((_) {
-                    pager.load(LoadType.append);
-                  });
-                }
+                // Schedules the request for the end of this frame.
+                WidgetsBinding.instance.addPostFrameCallback((_) {
+                  pager.load(LoadType.append);
+                });
               },
             ),
           ),
@@ -258,36 +238,24 @@ class _PagingSliverListState<Key, Value>
 
   SliverChildDelegate _createDelegate(
     List<LoadResultPage<Key, Value>> pages, {
-    VoidCallback? onBuildingPrependLoadTriggerItem,
     VoidCallback? onBuildingAppendLoadTriggerItem,
   }) {
     final items = pages.items;
     final itemCount = items.length;
     final prefetchIndex = pager.config.prefetchIndex;
 
     // Helper function to generate prepend and append load trigger notifications
-    void generatePrependAppendLoadTriggerNotification(int index) {
+    void generateAppendLoadTriggerNotification(int index) {
       // If there is no prefetch index, we don't have to generate any
       // notification.
       if (prefetchIndex == null) return;
 
-      // Generate notifications at the beginning and end of the list if the
-      // [itemCount] is less than [prefetchIndex].
-      if (prefetchIndex > itemCount) {
-        if (index == 0) onBuildingPrependLoadTriggerItem?.call();
-        if (index == itemCount - 1) onBuildingAppendLoadTriggerItem?.call();
-        return;
-      }
-
-      // Check if the index corresponds to near the top or bottom of the list.
-      final (nearTop, nearBottom) = (
-        index == prefetchIndex,
-        index == itemCount - prefetchIndex,
-      );
+      // Check if the index is close to the end of the list based on the
+      // prefetch index.
+      final shouldAppendItems = index >= itemCount - prefetchIndex;
 
-      // Generate notifications.
-      if (nearTop) onBuildingPrependLoadTriggerItem?.call();
-      if (nearBottom) onBuildingAppendLoadTriggerItem?.call();
+      // Generate notification.
+      if (shouldAppendItems) onBuildingAppendLoadTriggerItem?.call();
     }
 
     final itemBuilder = widget.itemBuilder;
@@ -297,8 +265,8 @@ class _PagingSliverListState<Key, Value>
         (BuildContext context, int index) {
           final int itemIndex = index ~/ 2;
           if (index.isEven) {
-            // Generate prepend and append notification.
-            generatePrependAppendLoadTriggerNotification(itemIndex);
+            // Generate append notification.
+            generateAppendLoadTriggerNotification(itemIndex);
 
             // Build items.
             return itemBuilder(context, itemIndex);
@@ -319,8 +287,8 @@ class _PagingSliverListState<Key, Value>
 
     return SliverChildBuilderDelegate(
       (BuildContext context, int index) {
-        // Generate prepend and append notification.
-        generatePrependAppendLoadTriggerNotification(index);
+        // Generate append notification.
+        generateAppendLoadTriggerNotification(index);
 
         // Build items.
         return itemBuilder(context, index);