[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;
+  }
+}