feat: add scrollNotificationPredicate

Author: LinXunFeng

lib/src/common/observer_widget.dart

@@ -48,6 +48,16 @@ class ObserverWidget<C extends ObserverController, M extends ObserveModel,
   /// child widget.
   final double toNextOverPercent;
 
+  /// A predicate for [ScrollNotification], used to determine whether
+  /// observation can be triggered.
+  ///
+  /// Generally combined with [defaultScrollNotificationPredicate] to check
+  /// whether `notification.depth == 0`, which means that the notification did
+  /// not bubble through any intervening scrolling widgets.
+  /// This can avoid the unnecessary observation calculations caused by
+  /// intervening scrolling widgets, which in turn improves performance.
+  final ScrollNotificationPredicate? scrollNotificationPredicate;
+
   /// Used to set types those can trigger observe automatically.
   ///
   /// Defaults to [.scrollStart, .scrollUpdate, .scrollEnd]
@@ -78,6 +88,7 @@ class ObserverWidget<C extends ObserverController, M extends ObserveModel,
     this.leadingOffset = 0,
     this.dynamicLeadingOffset,
     this.toNextOverPercent = 1,
+    this.scrollNotificationPredicate,
     this.autoTriggerObserveTypes,
     this.triggerOnObserveType =
         ObserverTriggerOnObserveType.displayingItemsChange,
@@ -152,6 +163,15 @@ class ObserverWidgetState<
       },
       child: NotificationListener<ScrollNotification>(
         onNotification: (notification) {
+          // If the scrollNotificationPredicate returns false, the notification
+          // will be ignored.
+          if (!(widget.scrollNotificationPredicate?.call(notification) ??
+              true)) {
+            return false;
+          }
+          // If the notification.runtimeType is not in the list of
+          // innerAutoTriggerObserveScrollNotifications that can trigger
+          // observation, the notification will be ignored.
           if (innerAutoTriggerObserveScrollNotifications
               .contains(notification.runtimeType)) {
             final isIgnoreInnerCanHandleObserve =

lib/src/gridview/grid_observer_view.dart

@@ -31,6 +31,7 @@ class GridViewObserver extends ObserverWidget<GridObserverController,
     double leadingOffset = 0,
     double Function()? dynamicLeadingOffset,
     double toNextOverPercent = 1,
+    ScrollNotificationPredicate? scrollNotificationPredicate,
     List<ObserverAutoTriggerObserveType>? autoTriggerObserveTypes,
     ObserverTriggerOnObserveType triggerOnObserveType =
         ObserverTriggerOnObserveType.displayingItemsChange,
@@ -46,6 +47,7 @@ class GridViewObserver extends ObserverWidget<GridObserverController,
           leadingOffset: leadingOffset,
           dynamicLeadingOffset: dynamicLeadingOffset,
           toNextOverPercent: toNextOverPercent,
+          scrollNotificationPredicate: scrollNotificationPredicate,
           autoTriggerObserveTypes: autoTriggerObserveTypes,
           triggerOnObserveType: triggerOnObserveType,
           customHandleObserve: customHandleObserve,

lib/src/listview/list_observer_view.dart

@@ -31,6 +31,7 @@ class ListViewObserver extends ObserverWidget<ListObserverController,
     double leadingOffset = 0,
     double Function()? dynamicLeadingOffset,
     double toNextOverPercent = 1,
+    ScrollNotificationPredicate? scrollNotificationPredicate,
     List<ObserverAutoTriggerObserveType>? autoTriggerObserveTypes,
     ObserverTriggerOnObserveType triggerOnObserveType =
         ObserverTriggerOnObserveType.displayingItemsChange,
@@ -46,6 +47,7 @@ class ListViewObserver extends ObserverWidget<ListObserverController,
           leadingOffset: leadingOffset,
           dynamicLeadingOffset: dynamicLeadingOffset,
           toNextOverPercent: toNextOverPercent,
+          scrollNotificationPredicate: scrollNotificationPredicate,
           autoTriggerObserveTypes: autoTriggerObserveTypes,
           triggerOnObserveType: triggerOnObserveType,
           customHandleObserve: customHandleObserve,

lib/src/sliver/sliver_observer_view.dart

@@ -51,6 +51,7 @@ class SliverViewObserver extends ObserverWidget<SliverObserverController,
     double Function()? dynamicLeadingOffset,
     this.customOverlap,
     double toNextOverPercent = 1,
+    ScrollNotificationPredicate? scrollNotificationPredicate,
     List<ObserverAutoTriggerObserveType>? autoTriggerObserveTypes,
     ObserverTriggerOnObserveType triggerOnObserveType =
         ObserverTriggerOnObserveType.displayingItemsChange,
@@ -66,6 +67,7 @@ class SliverViewObserver extends ObserverWidget<SliverObserverController,
           leadingOffset: leadingOffset,
           dynamicLeadingOffset: dynamicLeadingOffset,
           toNextOverPercent: toNextOverPercent,
+          scrollNotificationPredicate: scrollNotificationPredicate,
           autoTriggerObserveTypes: autoTriggerObserveTypes,
           triggerOnObserveType: triggerOnObserveType,
           customHandleObserve: customHandleObserve,