Merge pull request #1402 from EnsembleUI/scroll-notifier

onScroll callback for listview

Author: snehmehta

lib/layout/helpers/list_view_core.dart

@@ -69,6 +69,7 @@ class ListViewCore extends StatefulWidget {
     this.loadingBuilder,
     this.errorBuilder,
     this.separatorBuilder,
+    this.onScroll,
   });
 
   final bool shrinkWrap;
@@ -89,20 +90,27 @@ class ListViewCore extends StatefulWidget {
   final WidgetBuilder? errorBuilder;
   final IndexedWidgetBuilder? separatorBuilder;
   final ItemBuilder itemBuilder;
+  final void Function(double)? onScroll;
 
   @override
   State<ListViewCore> createState() => _ListViewCoreState();
 }
 
 class _ListViewCoreState extends State<ListViewCore> {
   late final Debouncer debounce;
+  late final Debouncer _scrollDebouce;
+  late final ScrollController _scrollController;
 
   int? _lastFetchedIndex;
 
   @override
   void initState() {
     super.initState();
     debounce = Debouncer(widget.debounceDuration);
+    _scrollDebouce = Debouncer(const Duration(milliseconds: 15));
+    _scrollController = widget.scrollController ?? ScrollController();
+    _scrollController.addListener(_onScroll);
+
     attemptFetch();
   }
 
@@ -116,8 +124,13 @@ class _ListViewCoreState extends State<ListViewCore> {
 
   @override
   void dispose() {
-    super.dispose();
+    _scrollController.removeListener(_onScroll);
+    if (widget.scrollController == null) {
+      _scrollController.dispose();
+    }
     debounce.cancel();
+    _scrollDebouce.cancel();
+    super.dispose();
   }
 
   void attemptFetch() {
@@ -135,6 +148,14 @@ class _ListViewCoreState extends State<ListViewCore> {
     }
   }
 
+  void _onScroll() {
+    if (widget.onScroll != null) {
+      _scrollDebouce.run(() {
+        widget.onScroll?.call(_scrollController.position.pixels);
+      });
+    }
+  }
+
   WidgetBuilder get loadingBuilder =>
       widget.loadingBuilder ??
       (context) => const Center(child: flutter.CircularProgressIndicator());
@@ -162,7 +183,7 @@ class _ListViewCoreState extends State<ListViewCore> {
       scrollDirection: widget.scrollDirection,
       reverse: widget.reverse,
       shrinkWrap: widget.shrinkWrap,
-      controller: widget.scrollController,
+      controller: _scrollController,
       physics: widget.physics,
       cacheExtent: widget.cacheExtent,
       slivers: [

lib/layout/list_view.dart

@@ -1,6 +1,7 @@
 import 'package:ensemble/action/haptic_action.dart';
 import 'package:ensemble/framework/action.dart';
 import 'package:ensemble/framework/error_handling.dart';
+import 'package:ensemble/framework/event.dart';
 import 'package:ensemble/framework/scope.dart';
 import 'package:ensemble/framework/studio/studio_debugger.dart';
 import 'package:ensemble/framework/view/data_scope_widget.dart';
@@ -79,6 +80,8 @@ class ListView extends StatefulWidget
           _controller.hasReachedMax = Utils.getBool(value, fallback: false),
       'loadingWidget': (value) => _controller.loadingWidget = value,
       'data': (value) => _controller.itemTemplate?.data = value,
+      'onScroll': (value) =>
+          controller.onScroll = EnsembleAction.fromYaml(value, initiator: this),
     };
   }
 
@@ -113,6 +116,7 @@ class ListViewController extends BoxLayoutController {
   bool hasReachedMax = false;
 
   ListViewState? widgetState;
+  EnsembleAction? onScroll;
 
   void _bind(ListViewState state) {
     widgetState = state;
@@ -177,6 +181,15 @@ class ListViewState extends WidgetState<ListView>
       isLoading: showLoading,
       onFetchData: _fetchData,
       hasReachedMax: widget._controller.hasReachedMax,
+      onScroll: (pixel) {
+        if (widget._controller.onScroll != null) {
+          ScreenController().executeAction(
+            context,
+            widget._controller.onScroll!,
+            event: EnsembleEvent(null, data: {'pixel': pixel}),
+          );
+        }
+      },
       scrollController: (footerScope != null &&
               footerScope.isColumnScrollableAndRoot(context))
           ? null