[UserListView] Use LazyLoadScrollView for pagination rather than listening scroll controller

lib/src/lazy_load_scroll_view.dart

@@ -0,0 +1,81 @@
+import 'package:flutter/widgets.dart';
+
+enum LoadingStatus { LOADING, STABLE }
+
+/// Signature for EndOfPageListeners
+typedef EndOfPageListenerCallback = void Function();
+
+/// A widget that wraps a [Widget] and will trigger [onEndOfPage] when it
+/// reaches the bottom of the list
+class LazyLoadScrollView extends StatefulWidget {
+  /// The [Widget] that this widget watches for changes on
+  final Widget child;
+
+  /// Called when the [child] reaches the end of the list
+  final EndOfPageListenerCallback onEndOfPage;
+
+  /// The offset to take into account when triggering [onEndOfPage] in pixels
+  final int scrollOffset;
+
+  /// Used to determine if loading of new data has finished. You should use set this if you aren't using a FutureBuilder or StreamBuilder
+  final bool isLoading;
+
+  LazyLoadScrollView({
+    Key key,
+    @required this.child,
+    @required this.onEndOfPage,
+    this.isLoading = false,
+    this.scrollOffset = 100,
+  })  : assert(onEndOfPage != null),
+        assert(child != null),
+        super(key: key);
+
+  @override
+  State<StatefulWidget> createState() => _LazyLoadScrollViewState();
+}
+
+class _LazyLoadScrollViewState extends State<LazyLoadScrollView> {
+  LoadingStatus _loadMoreStatus = LoadingStatus.STABLE;
+
+  @override
+  void didUpdateWidget(LazyLoadScrollView oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (!widget.isLoading) {
+      _loadMoreStatus = LoadingStatus.STABLE;
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return NotificationListener(
+      child: widget.child,
+      onNotification: _onNotification,
+    );
+  }
+
+  bool _onNotification(Notification notification) {
+    if (notification is ScrollUpdateNotification) {
+      if (notification.metrics.maxScrollExtent > notification.metrics.pixels &&
+          notification.metrics.maxScrollExtent - notification.metrics.pixels <=
+              widget.scrollOffset) {
+        if (_loadMoreStatus != null &&
+            _loadMoreStatus == LoadingStatus.STABLE) {
+          _loadMoreStatus = LoadingStatus.LOADING;
+          widget.onEndOfPage();
+        }
+      }
+      return true;
+    }
+    if (notification is OverscrollNotification) {
+      if (notification.overscroll > 0) {
+        if (_loadMoreStatus != null &&
+            _loadMoreStatus == LoadingStatus.STABLE) {
+          _loadMoreStatus = LoadingStatus.LOADING;
+          widget.onEndOfPage();
+        }
+      }
+      return true;
+    }
+    return false;
+  }
+}

lib/src/user_list_view.dart

@@ -2,6 +2,7 @@ import 'dart:convert';
 
 import 'package:flutter/material.dart';
 import 'package:stream_chat/stream_chat.dart';
+import 'package:stream_chat_flutter/src/lazy_load_scroll_view.dart';
 import 'package:stream_chat_flutter/src/users_bloc.dart';
 import 'package:stream_chat_flutter/stream_chat_flutter.dart';
 
@@ -144,8 +145,6 @@ class UserListView extends StatefulWidget {
 
 class _UserListViewState extends State<UserListView>
     with WidgetsBindingObserver {
-  final ScrollController _scrollController = ScrollController();
-
   bool get _isListView => widget.crossAxisCount == 1;
 
   @override
@@ -158,14 +157,6 @@ class _UserListViewState extends State<UserListView>
       pagination: widget.pagination,
       options: widget.options,
     );
-
-    _scrollController.addListener(() {
-      usersBloc.queryUsersLoading.first.then((loading) {
-        if (!loading) {
-          _listenUserPagination(usersBloc);
-        }
-      });
-    });
   }
 
   @override
@@ -327,32 +318,35 @@ class _UserListViewState extends State<UserListView>
           );
         }
 
-        if (_isListView) {
+        final child = _isListView
-          return ListView.separated(
+            ? ListView.separated(
-            physics: AlwaysScrollableScrollPhysics(),
+                physics: AlwaysScrollableScrollPhysics(),
-            controller: _scrollController,
+                // controller: _scrollController,
-            itemCount: items.isNotEmpty ? items.length + 1 : items.length,
+                itemCount: items.isNotEmpty ? items.length + 1 : items.length,
-            separatorBuilder: (_, index) {
+                separatorBuilder: (_, index) {
-              if (widget.separatorBuilder != null) {
+                  if (widget.separatorBuilder != null) {
-                return widget.separatorBuilder(context, index);
+                    return widget.separatorBuilder(context, index);
-              }
+                  }
-              return _separatorBuilder(context, index);
+                  return _separatorBuilder(context, index);
-            },
+                },
-            itemBuilder: (context, index) {
+                itemBuilder: (context, index) {
-              return _listItemBuilder(context, index, items);
+                  return _listItemBuilder(context, index, items);
-            },
+                },
-          );
+              )
-        }
+            : GridView.builder(
-        return GridView.builder(
+                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
-          gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
+                  crossAxisCount: widget.crossAxisCount,
-            crossAxisCount: widget.crossAxisCount,
+                ),
-          ),
+                itemCount: items.isNotEmpty ? items.length + 1 : items.length,
-          itemCount: items.isNotEmpty ? items.length + 1 : items.length,
+                physics: AlwaysScrollableScrollPhysics(),
-          physics: AlwaysScrollableScrollPhysics(),
+                itemBuilder: (context, index) {
-          controller: _scrollController,
+                  return _gridItemBuilder(context, index, items);
-          itemBuilder: (context, index) {
+                },
-            return _gridItemBuilder(context, index, items);
+              );
-          },
+
+        return LazyLoadScrollView(
+          onEndOfPage: () => _listenUserPagination(usersBlocState),
+          child: child,
         );
       },
     );
@@ -488,18 +482,14 @@ class _UserListViewState extends State<UserListView>
   }
 
   void _listenUserPagination(UsersBlocState usersProvider) {
-    if (_scrollController.position.maxScrollExtent ==
+    usersProvider.queryUsers(
-            _scrollController.offset &&
+      filter: widget.filter,
-        _scrollController.offset != 0) {
+      sort: widget.sort,
-      usersProvider.queryUsers(
+      pagination: widget.pagination.copyWith(
-        filter: widget.filter,
+        offset: usersProvider.users?.length ?? 0,
-        sort: widget.sort,
+      ),
-        pagination: widget.pagination.copyWith(
+      options: widget.options,
-          offset: usersProvider.users?.length ?? 0,
+    );
-        ),
-        options: widget.options,
-      );
-    }
   }
 
   @override