chore: linting

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/element_registry.dart

@@ -46,12 +46,12 @@ class _RegistryWidgetState extends State<RegistryWidget> {
 }
 
 class _InheritedRegistryWidget extends InheritedWidget {
-  final _RegistryWidgetState state;
-
   const _InheritedRegistryWidget(
       {Key? key, required this.state, required Widget child})
       : super(key: key, child: child);
 
+  final _RegistryWidgetState state;
+
   @override
   bool updateShouldNotify(InheritedWidget oldWidget) => true;
 }

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/indexed_key.dart

@@ -2,10 +2,13 @@ import 'dart:ui' show hashValues;
 
 import 'package:flutter/foundation.dart';
 
+/// {@template indexed_key}
+/// Creates an indexed key that delegates its [operator==] to the given key.
+///
+/// It contains an index used in [ScrollablePositionedList].
+/// {@endtemplate}
 class IndexedKey extends LocalKey {
-  /// Creates an indexed key that delegates its [operator==] to the given key.
+  /// {@macro indexed_key}
-  ///
-  /// It contains an index used in [ScrollablePositionedList].
   const IndexedKey(this.key, this.index);
 
   /// The key to which this this delegates its [operator==].
@@ -24,7 +27,5 @@ class IndexedKey extends LocalKey {
   int get hashCode => hashValues(runtimeType, key);
 
   @override
-  String toString() {
+  String toString() => '(IndexedKey) index: $index, key: $key';
-    return '(IndexedKey) index: $index, key: $key';
-  }
 }

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/item_positions_listener.dart

@@ -4,8 +4,8 @@
 
 import 'package:flutter/foundation.dart';
 
-import 'item_positions_notifier.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_notifier.dart';
-import 'scrollable_positioned_list.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/scrollable_positioned_list.dart';
 
 /// Provides a listenable iterable of [itemPositions] of items that are on
 /// screen and their locations.
@@ -57,5 +57,5 @@ class ItemPosition {
 
   @override
   String toString() =>
-      'ItemPosition(index: $index, itemLeadingEdge: $itemLeadingEdge, itemTrailingEdge: $itemTrailingEdge)';
+      '''ItemPosition(index: $index, itemLeadingEdge: $itemLeadingEdge, itemTrailingEdge: $itemTrailingEdge)''';
 }

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/item_positions_notifier.dart

@@ -4,7 +4,7 @@
 
 import 'package:flutter/foundation.dart';
 
-import 'item_positions_listener.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_listener.dart';
 
 /// Internal implementation of [ItemPositionsListener].
 class ItemPositionsNotifier implements ItemPositionsListener {

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/positioned_list.dart

@@ -8,11 +8,11 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 
-import 'element_registry.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/element_registry.dart';
-import 'indexed_key.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/indexed_key.dart';
-import 'item_positions_listener.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_listener.dart';
-import 'item_positions_notifier.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_notifier.dart';
-import 'scroll_view.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/scroll_view.dart';
 
 /// A list of widgets similar to [ListView], except scroll control
 /// and position reporting is based on index rather than pixel offset.
@@ -27,6 +27,7 @@ import 'scroll_view.dart';
 class PositionedList extends StatefulWidget {
   /// Create a [PositionedList].
   const PositionedList({
+    Key? key,
     required this.itemCount,
     required this.itemBuilder,
     this.separatorBuilder,
@@ -44,11 +45,12 @@ class PositionedList extends StatefulWidget {
     this.addSemanticIndexes = true,
     this.addRepaintBoundaries = true,
     this.addAutomaticKeepAlives = true,
-  })  : assert(itemCount != null),
+  })  : assert((positionedIndex == 0) || (positionedIndex < itemCount),
-        assert(itemBuilder != null),
+            'positionedIndex cannot be 0 and must be smaller than itemCount'),
-        assert((positionedIndex == 0) || (positionedIndex < itemCount));
+        super(key: key);
 
-  /// Called to find the new index of a child based on its key in case of reordering.
+  /// Called to find the new index of a child based on its key in case of
+  /// reordering.
   ///
   /// If not provided, a child widget may not map to its existing [RenderObject]
   /// when the order in which children are returned from [builder] changes.
@@ -263,7 +265,7 @@ class _PositionedListState extends State<PositionedList> {
           : widget.reverse
               ? widget.padding?.copyWith(left: 0)
               : widget.padding?.copyWith(right: 0)) ??
-      EdgeInsets.all(0);
+      const EdgeInsets.all(0);
 
   EdgeInsets get _centerSliverPadding => widget.scrollDirection == Axis.vertical
       ? widget.reverse
@@ -274,13 +276,13 @@ class _PositionedListState extends State<PositionedList> {
                   bottom: widget.positionedIndex == 0
                       ? widget.padding!.bottom
                       : 0) ??
-              EdgeInsets.all(0)
+              const EdgeInsets.all(0)
           : widget.padding?.copyWith(
                   top: widget.positionedIndex == 0 ? widget.padding!.top : 0,
                   bottom: widget.positionedIndex == widget.itemCount - 1
                       ? widget.padding!.bottom
                       : 0) ??
-              EdgeInsets.all(0)
+              const EdgeInsets.all(0)
       : widget.reverse
           ? widget.padding?.copyWith(
                   left: widget.positionedIndex == widget.itemCount - 1
@@ -289,23 +291,23 @@ class _PositionedListState extends State<PositionedList> {
                   right: widget.positionedIndex == 0
                       ? widget.padding!.right
                       : 0) ??
-              EdgeInsets.all(0)
+              const EdgeInsets.all(0)
           : widget.padding?.copyWith(
                 left: widget.positionedIndex == 0 ? widget.padding!.left : 0,
                 right: widget.positionedIndex == widget.itemCount - 1
                     ? widget.padding!.right
                     : 0,
               ) ??
-              EdgeInsets.all(0);
+              const EdgeInsets.all(0);
 
   EdgeInsets get _trailingSliverPadding =>
       widget.scrollDirection == Axis.vertical
           ? widget.reverse
-              ? widget.padding?.copyWith(bottom: 0) ?? EdgeInsets.all(0)
+              ? widget.padding?.copyWith(bottom: 0) ?? const EdgeInsets.all(0)
-              : widget.padding?.copyWith(top: 0) ?? EdgeInsets.all(0)
+              : widget.padding?.copyWith(top: 0) ?? const EdgeInsets.all(0)
           : widget.reverse
-              ? widget.padding?.copyWith(right: 0) ?? EdgeInsets.all(0)
+              ? widget.padding?.copyWith(right: 0) ?? const EdgeInsets.all(0)
-              : widget.padding?.copyWith(left: 0) ?? EdgeInsets.all(0);
+              : widget.padding?.copyWith(left: 0) ?? const EdgeInsets.all(0);
 
   void _schedulePositionNotificationUpdate() {
     if (!updateScheduled) {
@@ -317,10 +319,10 @@ class _PositionedListState extends State<PositionedList> {
         }
         final positions = <ItemPosition>[];
         RenderViewport? viewport;
-        for (var element in registeredElements.value!) {
+        for (final element in registeredElements.value!) {
-          final RenderBox box = element.renderObject as RenderBox;
+          final box = element.renderObject as RenderBox;
           viewport ??= RenderAbstractViewport.of(box) as RenderViewport?;
-          final IndexedKey key = element.widget.key as IndexedKey;
+          final key = element.widget.key as IndexedKey;
           if (widget.scrollDirection == Axis.vertical) {
             final reveal = viewport!.getOffsetToReveal(box, 0).offset;
             final itemOffset = reveal -

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/post_mount_callback.dart

@@ -29,7 +29,7 @@ class _PostMountCallbackElement extends StatelessElement {
   @override
   void mount(Element? parent, dynamic newSlot) {
     super.mount(parent, newSlot);
-    final PostMountCallback postMountCallback = widget as PostMountCallback;
+    final postMountCallback = widget as PostMountCallback;
     postMountCallback.callback?.call();
   }
 }

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/scroll_view.dart

@@ -6,11 +6,14 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
-import 'viewport.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/viewport.dart';
 
-/// A version of [CustomScrollView] that allows does not constrict the extents
+/// {@template custom_scroll_view}
+/// A version of [CustomScrollView] that does not constrict the extents
 /// to be within 0 and 1. See [CustomScrollView] for more information.
+/// {@endtemplate}
 class UnboundedCustomScrollView extends CustomScrollView {
+  /// {@macro custom_scroll_view}
   const UnboundedCustomScrollView({
     Key? key,
     Axis scrollDirection = Axis.vertical,

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/scrollable_positioned_list.dart

@@ -10,10 +10,10 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 
-import 'item_positions_listener.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_listener.dart';
-import 'item_positions_notifier.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/item_positions_notifier.dart';
-import 'positioned_list.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/positioned_list.dart';
-import 'post_mount_callback.dart';
+import 'package:stream_chat_flutter/src/scrollable_positioned_list/src/post_mount_callback.dart';
 
 /// Number of screens to scroll when scrolling a long distance.
 const int _screenScrollCount = 2;
@@ -52,9 +52,7 @@ class ScrollablePositionedList extends StatefulWidget {
     this.addRepaintBoundaries = true,
     this.minCacheExtent,
     this.findChildIndexCallback,
-  })  : assert(itemCount != null),
+  })  : itemPositionsNotifier = itemPositionsListener as ItemPositionsNotifier?,
-        assert(itemBuilder != null),
-        itemPositionsNotifier = itemPositionsListener as ItemPositionsNotifier?,
         separatorBuilder = null,
         super(key: key);
 
@@ -79,13 +77,12 @@ class ScrollablePositionedList extends StatefulWidget {
     this.addRepaintBoundaries = true,
     this.minCacheExtent,
     this.findChildIndexCallback,
-  })  : assert(itemCount != null),
+  })  : assert(separatorBuilder != null, 'seperatorBuilder cannot be null'),
-        assert(itemBuilder != null),
-        assert(separatorBuilder != null),
         itemPositionsNotifier = itemPositionsListener as ItemPositionsNotifier?,
         super(key: key);
 
-  /// Called to find the new index of a child based on its key in case of reordering.
+  /// Called to find the new index of a child based on its key in case of
+  /// reordering.
   ///
   /// If not provided, a child widget may not map to its existing [RenderObject]
   /// when the order in which children are returned from [builder] changes.
@@ -235,9 +232,11 @@ class ItemScrollController {
     Curve curve = Curves.linear,
     List<double> opacityAnimationWeights = const [40, 20, 40],
   }) {
-    assert(_scrollableListState != null);
+    assert(_scrollableListState != null, '_scrollableListState cannot be null');
-    assert(opacityAnimationWeights.length == 3);
+    assert(opacityAnimationWeights.length == 3,
-    assert(duration > Duration.zero);
+        'opacityAnimationWeights.length is not equal to 3');
+    assert(duration > Duration.zero,
+        'duration needs to be bigger than Duration.zero');
     return _scrollableListState!._scrollTo(
       index: index,
       alignment: alignment,
@@ -248,7 +247,8 @@ class ItemScrollController {
   }
 
   void _attach(_ScrollablePositionedListState scrollableListState) {
-    assert(_scrollableListState == null);
+    assert(
+        _scrollableListState == null, '_scrollableListState needs to be null');
     _scrollableListState = scrollableListState;
   }
 
@@ -260,11 +260,11 @@ class ItemScrollController {
 class _ScrollablePositionedListState extends State<ScrollablePositionedList>
     with TickerProviderStateMixin {
   /// Details for the primary (active) [ListView].
-  var primary = _ListDisplayDetails(const ValueKey('Ping'));
+  _ListDisplayDetails primary = _ListDisplayDetails(const ValueKey('Ping'));
 
   /// Details for the secondary (transitional) [ListView] that is temporarily
   /// shown when scrolling a long distance.
-  var secondary = _ListDisplayDetails(const ValueKey('Pong'));
+  _ListDisplayDetails secondary = _ListDisplayDetails(const ValueKey('Pong'));
 
   final opacity = ProxyAnimation(const AlwaysStoppedAnimation<double>(0));
 
@@ -275,10 +275,11 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
   @override
   void initState() {
     super.initState();
-    ItemPosition? initialPosition = PageStorage.of(context)!.readState(context);
+    final ItemPosition? initialPosition =
-    primary.target = initialPosition?.index ?? widget.initialScrollIndex;
+        PageStorage.of(context)!.readState(context);
-    primary.alignment =
+    primary
-        initialPosition?.itemLeadingEdge ?? widget.initialAlignment;
+      ..target = initialPosition?.index ?? widget.initialScrollIndex
+      ..alignment = initialPosition?.itemLeadingEdge ?? widget.initialAlignment;
     if (widget.itemCount > 0 && primary.target > widget.itemCount - 1) {
       primary.target = widget.itemCount - 1;
     }
@@ -333,79 +334,78 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
   }
 
   @override
-  Widget build(BuildContext context) {
+  Widget build(BuildContext context) => LayoutBuilder(
-    return LayoutBuilder(
+        builder: (context, constraints) {
-      builder: (context, constraints) {
+          final cacheExtent = _cacheExtent(constraints);
-        final cacheExtent = _cacheExtent(constraints);
+          return GestureDetector(
-        return GestureDetector(
+            onPanDown: (_) => _stopScroll(canceled: true),
-          onPanDown: (_) => _stopScroll(canceled: true),
+            excludeFromSemantics: true,
-          excludeFromSemantics: true,
+            child: Stack(
-          child: Stack(
+              children: <Widget>[
-            children: <Widget>[
-              PostMountCallback(
-                key: primary.key,
-                callback: startAnimationCallback,
-                child: FadeTransition(
-                  opacity: ReverseAnimation(opacity),
-                  child: NotificationListener<ScrollNotification>(
-                    onNotification: (_) => _isTransitioning,
-                    child: PositionedList(
-                      itemBuilder: widget.itemBuilder,
-                      separatorBuilder: widget.separatorBuilder,
-                      itemCount: widget.itemCount,
-                      positionedIndex: primary.target,
-                      controller: primary.scrollController,
-                      itemPositionsNotifier: primary.itemPositionsNotifier,
-                      scrollDirection: widget.scrollDirection,
-                      reverse: widget.reverse,
-                      cacheExtent: cacheExtent,
-                      alignment: primary.alignment,
-                      physics: widget.physics,
-                      addSemanticIndexes: widget.addSemanticIndexes,
-                      semanticChildCount: widget.semanticChildCount,
-                      padding: widget.padding,
-                      addAutomaticKeepAlives: widget.addAutomaticKeepAlives,
-                      addRepaintBoundaries: widget.addRepaintBoundaries,
-                      findChildIndexCallback: widget.findChildIndexCallback,
-                    ),
-                  ),
-                ),
-              ),
-              if (_isTransitioning)
                 PostMountCallback(
-                  key: secondary.key,
+                  key: primary.key,
                   callback: startAnimationCallback,
                   child: FadeTransition(
-                    opacity: opacity,
+                    opacity: ReverseAnimation(opacity),
                     child: NotificationListener<ScrollNotification>(
-                      onNotification: (_) => false,
+                      onNotification: (_) => _isTransitioning,
                       child: PositionedList(
                         itemBuilder: widget.itemBuilder,
                         separatorBuilder: widget.separatorBuilder,
                         itemCount: widget.itemCount,
-                        itemPositionsNotifier: secondary.itemPositionsNotifier,
+                        positionedIndex: primary.target,
-                        positionedIndex: secondary.target,
+                        controller: primary.scrollController,
-                        controller: secondary.scrollController,
+                        itemPositionsNotifier: primary.itemPositionsNotifier,
                         scrollDirection: widget.scrollDirection,
                         reverse: widget.reverse,
                         cacheExtent: cacheExtent,
-                        alignment: secondary.alignment,
+                        alignment: primary.alignment,
                         physics: widget.physics,
                         addSemanticIndexes: widget.addSemanticIndexes,
                         semanticChildCount: widget.semanticChildCount,
                         padding: widget.padding,
                         addAutomaticKeepAlives: widget.addAutomaticKeepAlives,
                         addRepaintBoundaries: widget.addRepaintBoundaries,
+                        findChildIndexCallback: widget.findChildIndexCallback,
                       ),
                     ),
                   ),
                 ),
-            ],
+                if (_isTransitioning)
-          ),
+                  PostMountCallback(
-        );
+                    key: secondary.key,
-      },
+                    callback: startAnimationCallback,
-    );
+                    child: FadeTransition(
-  }
+                      opacity: opacity,
+                      child: NotificationListener<ScrollNotification>(
+                        onNotification: (_) => false,
+                        child: PositionedList(
+                          itemBuilder: widget.itemBuilder,
+                          separatorBuilder: widget.separatorBuilder,
+                          itemCount: widget.itemCount,
+                          itemPositionsNotifier:
+                              secondary.itemPositionsNotifier,
+                          positionedIndex: secondary.target,
+                          controller: secondary.scrollController,
+                          scrollDirection: widget.scrollDirection,
+                          reverse: widget.reverse,
+                          cacheExtent: cacheExtent,
+                          alignment: secondary.alignment,
+                          physics: widget.physics,
+                          addSemanticIndexes: widget.addSemanticIndexes,
+                          semanticChildCount: widget.semanticChildCount,
+                          padding: widget.padding,
+                          addAutomaticKeepAlives: widget.addAutomaticKeepAlives,
+                          addRepaintBoundaries: widget.addRepaintBoundaries,
+                        ),
+                      ),
+                    ),
+                  ),
+              ],
+            ),
+          );
+        },
+      );
 
   double _cacheExtent(BoxConstraints constraints) => max(
         constraints.maxHeight * _screenScrollCount,
@@ -419,8 +419,9 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
     }
     setState(() {
       primary.scrollController.jumpTo(0);
-      primary.target = index;
+      primary
-      primary.alignment = alignment;
+        ..target = index
+        ..alignment = alignment;
     });
   }
 
@@ -505,8 +506,9 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
       setState(() {
         // TODO: _startScroll can be re-entrant, which invalidates this assert.
         // assert(!_isTransitioning);
-        secondary.target = index;
+        secondary
-        secondary.alignment = alignment;
+          ..target = index
+          ..alignment = alignment;
         _isTransitioning = true;
       });
       await Future.wait<void>([startCompleter.future, endCompleter.future]);
@@ -532,7 +534,7 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
       if (opacity.value >= 0.5) {
         // Secondary [ListView] is more visible than the primary; make it the
         // new primary.
-        var temp = primary;
+        final temp = primary;
         primary = secondary;
         secondary = temp;
       }
@@ -542,8 +544,8 @@ class _ScrollablePositionedListState extends State<ScrollablePositionedList>
   }
 
   Animatable<double> _opacityAnimation(List<double> opacityAnimationWeights) {
-    final startOpacity = 0.0;
+    const startOpacity = 0.0;
-    final endOpacity = 1.0;
+    const endOpacity = 1.0;
     return TweenSequence<double>(<TweenSequenceItem<double>>[
       TweenSequenceItem<double>(
           tween: ConstantTween<double>(startOpacity),

packages/stream_chat_flutter/lib/src/scrollable_positioned_list/src/viewport.dart

@@ -2,17 +2,22 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// ignore_for_file: lines_longer_than_80_chars
+
 import 'dart:math' as math;
 
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
+/// {@template unbounded_viewport}
 /// A render object that is bigger on the inside.
 ///
 /// Version of [Viewport] with some modifications to how extents are
 /// computed to allow scroll extents outside 0 to 1.  See [Viewport]
 /// for more information.
+/// description
 class UnboundedViewport extends Viewport {
+  /// {@macro unbounded_viewport}
   UnboundedViewport({
     Key? key,
     AxisDirection axisDirection = AxisDirection.down,
@@ -40,16 +45,15 @@ class UnboundedViewport extends Viewport {
   double get anchor => _anchor;
 
   @override
-  RenderViewport createRenderObject(BuildContext context) {
+  RenderViewport createRenderObject(BuildContext context) =>
-    return UnboundedRenderViewport(
+      UnboundedRenderViewport(
-      axisDirection: axisDirection,
+        axisDirection: axisDirection,
-      crossAxisDirection: crossAxisDirection ??
+        crossAxisDirection: crossAxisDirection ??
-          Viewport.getDefaultCrossAxisDirection(context, axisDirection),
+            Viewport.getDefaultCrossAxisDirection(context, axisDirection),
-      anchor: anchor,
+        anchor: anchor,
-      offset: offset,
+        offset: offset,
-      cacheExtent: cacheExtent,
+        cacheExtent: cacheExtent,
-    );
+      );
-  }
 }
 
 /// A render object that is bigger on the inside.
@@ -100,7 +104,6 @@ class UnboundedRenderViewport extends RenderViewport {
 
   @override
   set anchor(double value) {
-    assert(value != null);
     if (value == _anchor) return;
     _anchor = value;
     markNeedsLayout();
@@ -124,8 +127,6 @@ class UnboundedRenderViewport extends RenderViewport {
 
   @override
   Rect describeSemanticsClip(RenderSliver? child) {
-    assert(axis != null);
-
     if (_calculatedCacheExtent == null) {
       return semanticBounds;
     }
@@ -151,14 +152,14 @@ class UnboundedRenderViewport extends RenderViewport {
   @override
   void performLayout() {
     if (center == null) {
-      assert(firstChild == null);
+      assert(firstChild == null, 'firstChild cannot be null');
       _minScrollExtent = 0.0;
       _maxScrollExtent = 0.0;
       _hasVisualOverflow = false;
-      offset.applyContentDimensions(0.0, 0.0);
+      offset.applyContentDimensions(0, 0);
       return;
     }
-    assert(center!.parent == this);
+    assert(center!.parent == this, 'center.parent cannot be equal to this');
 
     late double mainAxisExtent;
     late double crossAxisExtent;
@@ -178,7 +179,6 @@ class UnboundedRenderViewport extends RenderViewport {
     double correction;
     var count = 0;
     do {
-      assert(offset.pixels != null);
       correction = _attemptLayout(mainAxisExtent, crossAxisExtent,
           offset.pixels + centerOffsetAdjustment);
       if (correction != 0.0) {
@@ -187,17 +187,18 @@ class UnboundedRenderViewport extends RenderViewport {
         // *** Difference from [RenderViewport].
         final top = _minScrollExtent + mainAxisExtent * anchor;
         final bottom = _maxScrollExtent - mainAxisExtent * (1.0 - anchor);
-        final maxScrollOffset = math.max(math.min(0.0, top), bottom);
+        final maxScrollOffset = math.max<double>(math.min(0, top), bottom);
-        final minScrollOffset = math.min(top, maxScrollOffset);
+        final minScrollOffset = math.min<double>(top, maxScrollOffset);
-        if (offset.applyContentDimensions(minScrollOffset, maxScrollOffset))
+        if (offset.applyContentDimensions(minScrollOffset, maxScrollOffset)) {
           break;
+        }
         // *** End of difference from [RenderViewport].
       }
       count += 1;
     } while (count < _maxLayoutCycles);
     assert(() {
       if (count >= _maxLayoutCycles) {
-        assert(count != 1);
+        assert(count != 1, 'count not equal to 1');
         throw FlutterError(
             'A RenderViewport exceeded its maximum number of layout cycles.\n'
             'RenderViewport render objects, during layout, can retry if either their '
@@ -217,16 +218,16 @@ class UnboundedRenderViewport extends RenderViewport {
             ' layout passes.');
       }
       return true;
-    }());
+    }(), 'count needs to be bigger than _maxLayoutCycles');
   }
 
   double _attemptLayout(
       double mainAxisExtent, double crossAxisExtent, double correctedOffset) {
-    assert(!mainAxisExtent.isNaN);
+    assert(!mainAxisExtent.isNaN, 'assert mainAxisExtent.isNaN');
-    assert(mainAxisExtent >= 0.0);
+    assert(mainAxisExtent >= 0.0, 'assert mainAxisExtent >= 0.0');
-    assert(crossAxisExtent.isFinite);
+    assert(crossAxisExtent.isFinite, 'assert crossAxisExtent.isFinite');
-    assert(crossAxisExtent >= 0.0);
+    assert(crossAxisExtent >= 0.0, 'assert crossAxisExtent >= 0.0');
-    assert(correctedOffset.isFinite);
+    assert(correctedOffset.isFinite, 'assert correctedOffset.isFinite');
     _minScrollExtent = 0.0;
     _maxScrollExtent = 0.0;
     _hasVisualOverflow = false;
@@ -234,10 +235,10 @@ class UnboundedRenderViewport extends RenderViewport {
     // centerOffset is the offset from the leading edge of the RenderViewport
     // to the zero scroll offset (the line between the forward slivers and the
     // reverse slivers).
-    final double centerOffset = mainAxisExtent * anchor - correctedOffset;
+    final centerOffset = mainAxisExtent * anchor - correctedOffset;
-    final double reverseDirectionRemainingPaintExtent =
+    final reverseDirectionRemainingPaintExtent =
         centerOffset.clamp(0.0, mainAxisExtent);
-    final double forwardDirectionRemainingPaintExtent =
+    final forwardDirectionRemainingPaintExtent =
         (mainAxisExtent - centerOffset).clamp(0.0, mainAxisExtent);
 
     switch (cacheExtentStyle) {
@@ -249,21 +250,21 @@ class UnboundedRenderViewport extends RenderViewport {
         break;
     }
 
-    final double fullCacheExtent = mainAxisExtent + 2 * _calculatedCacheExtent!;
+    final fullCacheExtent = mainAxisExtent + 2 * _calculatedCacheExtent!;
-    final double centerCacheOffset = centerOffset + _calculatedCacheExtent!;
+    final centerCacheOffset = centerOffset + _calculatedCacheExtent!;
-    final double reverseDirectionRemainingCacheExtent =
+    final reverseDirectionRemainingCacheExtent =
         centerCacheOffset.clamp(0.0, fullCacheExtent);
-    final double forwardDirectionRemainingCacheExtent =
+    final forwardDirectionRemainingCacheExtent =
         (fullCacheExtent - centerCacheOffset).clamp(0.0, fullCacheExtent);
 
-    final RenderSliver? leadingNegativeChild = childBefore(center!);
+    final leadingNegativeChild = childBefore(center!);
 
     if (leadingNegativeChild != null) {
       // negative scroll offsets
-      final double result = layoutChildSequence(
+      final result = layoutChildSequence(
         child: leadingNegativeChild,
         scrollOffset: math.max(mainAxisExtent, centerOffset) - mainAxisExtent,
-        overlap: 0.0,
+        overlap: 0,
         layoutOffset: forwardDirectionRemainingPaintExtent,
         remainingPaintExtent: reverseDirectionRemainingPaintExtent,
         mainAxisExtent: mainAxisExtent,
@@ -280,9 +281,8 @@ class UnboundedRenderViewport extends RenderViewport {
     // positive scroll offsets
     return layoutChildSequence(
       child: center,
-      scrollOffset: math.max(0.0, -centerOffset),
+      scrollOffset: math.max(0, -centerOffset),
-      overlap:
+      overlap: leadingNegativeChild == null ? math.min(0, -centerOffset) : 0.0,
-          leadingNegativeChild == null ? math.min(0.0, -centerOffset) : 0.0,
       layoutOffset: centerOffset >= mainAxisExtent
           ? centerOffset
           : reverseDirectionRemainingPaintExtent,

packages/stream_chat_flutter/test/src/scrollable_positioned_list/reversed_positioned_list_test.dart

@@ -117,7 +117,7 @@ void main() {
   });
 
   testWidgets('List positioned with 15 at bottom', (WidgetTester tester) async {
-    await setUpWidgetTest(tester, topItem: 15, anchor: 0);
+    await setUpWidgetTest(tester, topItem: 15);
     await tester.pump();
 
     expect(find.text('Item 14'), findsNothing);

packages/stream_chat_flutter/test/src/scrollable_positioned_list/scrollable_positioned_list_test.dart

@@ -50,7 +50,8 @@ void main() {
           itemCount: itemCount,
           itemScrollController: itemScrollController,
           itemBuilder: (context, index) {
-            assert(index >= 0 && index <= itemCount - 1);
+            assert(index >= 0 && index <= itemCount - 1,
+                '''index needs to be bigger or equal to 0 and smallert than itemCount -1''');
             return SizedBox(
               height:
                   variableHeight ? (itemHeight + (index % 13) * 5) : itemHeight,
@@ -256,7 +257,7 @@ void main() {
         initialAlignment: 0.5);
 
     unawaited(itemScrollController.scrollTo(
-        index: 16, duration: scrollDuration, alignment: 1.0));
+        index: 16, duration: scrollDuration, alignment: 1));
     await tester.pump();
     await tester.pump();
     await tester.pump(scrollDuration + scrollDurationTolerance);
@@ -457,7 +458,7 @@ void main() {
     final itemScrollController = ItemScrollController();
     await setUpWidgetTest(tester, itemScrollController: itemScrollController);
 
-    var fadeTransitionFinder = find.descendant(
+    final fadeTransitionFinder = find.descendant(
         of: find.byType(ScrollablePositionedList),
         matching: find.byType(FadeTransition));
 
@@ -687,7 +688,7 @@ void main() {
         itemScrollController: itemScrollController,
         itemPositionsListener: itemPositionsListener);
 
-    itemScrollController.jumpTo(index: 100, alignment: 1.0);
+    itemScrollController.jumpTo(index: 100, alignment: 1);
     await tester.pump();
     await tester.pump();
     await tester.pump(scrollDuration + scrollDurationTolerance);
@@ -758,7 +759,7 @@ void main() {
         itemPositionsListener: itemPositionsListener);
 
     unawaited(itemScrollController.scrollTo(
-        index: 100, alignment: 1.0, duration: scrollDuration));
+        index: 100, alignment: 1, duration: scrollDuration));
     await tester.pump();
     await tester.pump();
     await tester.pump(scrollDuration + scrollDurationTolerance);
@@ -1138,13 +1139,13 @@ void main() {
     expect(find.text('Item 100'), findsNothing);
     expect(find.text('Item 200'), findsNothing);
 
-    var itemFinder = find.text('Item 300');
+    final itemFinder = find.text('Item 300');
     expect(itemFinder, findsOneWidget);
     expect(tester.getTopLeft(itemFinder).dy, 0);
   }, skip: true);
 
   testWidgets(
-      'Jump to 400 at bottom, manually scroll, scroll to 100 at bottom and back',
+      '''Jump to 400 at bottom, manually scroll, scroll to 100 at bottom and back''',
       (WidgetTester tester) async {
     final itemScrollController = ItemScrollController();
     final itemPositionsListener = ItemPositionsListener.create();
@@ -1168,7 +1169,7 @@ void main() {
         index: 400, alignment: 1, duration: scrollDuration));
     await tester.pumpAndSettle();
 
-    var itemFinder = find.text('Item 399');
+    final itemFinder = find.text('Item 399');
     expect(itemFinder, findsOneWidget);
     expect(tester.getBottomLeft(itemFinder).dy, screenHeight);
   });
@@ -1537,7 +1538,7 @@ void main() {
   });
 
   testWidgets('List can be keyed', (WidgetTester tester) async {
-    final key = ValueKey('key');
+    const key = ValueKey('key');
 
     await setUpWidgetTest(tester, key: key);
 
@@ -1559,7 +1560,7 @@ void main() {
         home: PageView(
           children: [
             KeyedSubtree(
-              key: PageStorageKey('key'),
+              key: const PageStorageKey('key'),
               child: ScrollablePositionedList.builder(
                 itemCount: defaultItemCount,
                 itemScrollController: itemScrollController,
@@ -1570,7 +1571,7 @@ void main() {
                 itemPositionsListener: itemPositionsListener,
               ),
             ),
-            Center(
+            const Center(
               child: Text('Test'),
             )
           ],
@@ -1616,7 +1617,7 @@ void main() {
         home: PageView(
           children: [
             KeyedSubtree(
-              key: PageStorageKey('key'),
+              key: const PageStorageKey('key'),
               child: ScrollablePositionedList.builder(
                 itemCount: defaultItemCount,
                 itemScrollController: itemScrollController,
@@ -1627,7 +1628,7 @@ void main() {
                 itemPositionsListener: itemPositionsListener,
               ),
             ),
-            Center(
+            const Center(
               child: Text('Test'),
             )
           ],
@@ -1663,7 +1664,7 @@ void main() {
   });
 
   testWidgets(
-      'Maintain programmatic and user position (9 half way off top) in page view',
+      '''Maintain programmatic and user position (9 half way off top) in page view''',
       (WidgetTester tester) async {
     final itemPositionsListener = ItemPositionsListener.create();
     final itemScrollController = ItemScrollController();
@@ -1677,7 +1678,7 @@ void main() {
         home: PageView(
           children: [
             KeyedSubtree(
-              key: PageStorageKey('key'),
+              key: const PageStorageKey('key'),
               child: ScrollablePositionedList.builder(
                 itemCount: defaultItemCount,
                 itemScrollController: itemScrollController,
@@ -1688,7 +1689,7 @@ void main() {
                 itemPositionsListener: itemPositionsListener,
               ),
             ),
-            Center(
+            const Center(
               child: Text('Test'),
             )
           ],
@@ -1728,7 +1729,7 @@ void main() {
         (itemHeight / screenHeight) / 2);
   });
 
-  testWidgets("List with no items", (WidgetTester tester) async {
+  testWidgets('List with no items', (WidgetTester tester) async {
     final itemScrollController = ItemScrollController();
     await setUpWidgetTest(tester,
         itemScrollController: itemScrollController, itemCount: 0);
@@ -1750,22 +1751,21 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<int>(
           valueListenable: itemCount,
-          builder: (context, itemCount, child) {
+          builder: (context, itemCount, child) =>
-            return ScrollablePositionedList.builder(
+              ScrollablePositionedList.builder(
-              initialScrollIndex: min(100, itemCount),
+            initialScrollIndex: min(100, itemCount),
-              initialAlignment: 0,
+            itemCount: itemCount,
-              itemCount: itemCount,
+            itemScrollController: itemScrollController,
-              itemScrollController: itemScrollController,
+            itemPositionsListener: itemPositionsListener,
-              itemPositionsListener: itemPositionsListener,
+            itemBuilder: (context, index) {
-              itemBuilder: (context, index) {
+              assert(index >= 0 && index <= itemCount - 1,
-                assert(index >= 0 && index <= itemCount - 1);
+                  'index not bigger than 0 and smaller than itemCount - 1');
-                return SizedBox(
+              return SizedBox(
-                  height: itemHeight,
+                height: itemHeight,
-                  child: Text('Item $index'),
+                child: Text('Item $index'),
-                );
+              );
-              },
+            },
-            );
+          ),
-          },
         ),
       ),
     );
@@ -1795,20 +1795,19 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<int>(
           valueListenable: itemCount,
-          builder: (context, itemCount, child) {
+          builder: (context, itemCount, child) =>
-            return ScrollablePositionedList.builder(
+              ScrollablePositionedList.builder(
-              initialScrollIndex: min(100, itemCount - 1),
+            initialScrollIndex: min(100, itemCount - 1),
-              initialAlignment: 0,
+            itemCount: itemCount,
-              itemCount: itemCount,
+            itemBuilder: (context, index) {
-              itemBuilder: (context, index) {
+              assert(index >= 0 && index <= itemCount - 1,
-                assert(index >= 0 && index <= itemCount - 1);
+                  'index not bigger than 0 and smaller than itemCount -1');
-                return SizedBox(
+              return SizedBox(
-                  height: itemHeight,
+                height: itemHeight,
-                  child: Text('Item $index'),
+                child: Text('Item $index'),
-                );
+              );
-              },
+            },
-            );
+          ),
-          },
         ),
       ),
     );
@@ -1835,19 +1834,19 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<int>(
           valueListenable: itemCount,
-          builder: (context, itemCount, child) {
+          builder: (context, itemCount, child) =>
-            return ScrollablePositionedList.builder(
+              ScrollablePositionedList.builder(
-              initialScrollIndex: itemCount - 1,
+            initialScrollIndex: itemCount - 1,
-              itemCount: itemCount,
+            itemCount: itemCount,
-              itemBuilder: (context, index) {
+            itemBuilder: (context, index) {
-                assert(index >= 0 && index <= itemCount - 1);
+              assert(index >= 0 && index <= itemCount - 1,
-                return SizedBox(
+                  'index not bigger than 0 and smaller than itemCount -1');
-                  height: itemHeight,
+              return SizedBox(
-                  child: Text('Item $index'),
+                height: itemHeight,
-                );
+                child: Text('Item $index'),
-              },
+              );
-            );
+            },
-          },
+          ),
         ),
       ),
     );
@@ -1948,7 +1947,6 @@ void main() {
       tester,
       itemCount: 2,
       initialAlignment: alignment,
-      initialIndex: 0,
     );
 
     await tester.pumpAndSettle();
@@ -1960,35 +1958,31 @@ void main() {
     tester.binding.window.devicePixelRatioTestValue = 1.0;
     tester.binding.window.physicalSizeTestValue =
         const Size(screenWidth, screenHeight);
-    final key = ValueNotifier<Key>(ValueKey('key'));
+    final key = ValueNotifier<Key>(const ValueKey('key'));
     final itemScrollController = ItemScrollController();
 
     await tester.pumpWidget(
       MaterialApp(
         home: ValueListenableBuilder<Key>(
           valueListenable: key,
-          builder: (context, key, child) {
+          builder: (context, key, child) => Container(
-            return Container(
+            key: key,
-              key: key,
+            child: ScrollablePositionedList.builder(
-              child: ScrollablePositionedList.builder(
+              itemCount: 200,
-                itemCount: 200,
+              itemScrollController: itemScrollController,
-                itemScrollController: itemScrollController,
+              itemBuilder: (context, index) => SizedBox(
-                itemBuilder: (context, index) {
+                height: itemHeight,
-                  return SizedBox(
+                child: Text('Item $index'),
-                    height: itemHeight,
-                    child: Text('Item $index'),
-                  );
-                },
               ),
-            );
+            ),
-          },
+          ),
         ),
       ),
     );
 
     await tester.pumpAndSettle();
 
-    key.value = ValueKey('newKey');
+    key.value = const ValueKey('newKey');
     await tester.pumpAndSettle();
 
     unawaited(
@@ -2003,9 +1997,9 @@ void main() {
     tester.binding.window.devicePixelRatioTestValue = 1.0;
     tester.binding.window.physicalSizeTestValue =
         const Size(screenWidth, screenHeight);
-    final outerKey = ValueNotifier<Key>(ValueKey('outerKey'));
+    final outerKey = ValueNotifier<Key>(const ValueKey('outerKey'));
     final innerKey = GlobalKey();
-    final listKey = ValueNotifier<Key>(ValueKey(null));
+    final listKey = ValueNotifier<Key>(const ValueKey(null));
     final itemScrollController = ItemScrollController();
 
     await tester.pumpWidget(
@@ -2038,8 +2032,8 @@ void main() {
 
     await tester.pumpAndSettle();
 
-    outerKey.value = ValueKey('newOuterKey');
+    outerKey.value = const ValueKey('newOuterKey');
-    listKey.value = ValueKey('newListKey');
+    listKey.value = const ValueKey('newListKey');
     await tester.pumpAndSettle();
 
     unawaited(
@@ -2053,33 +2047,29 @@ void main() {
     tester.binding.window.devicePixelRatioTestValue = 1.0;
     tester.binding.window.physicalSizeTestValue =
         const Size(screenWidth, screenHeight);
-    final key = ValueNotifier<Key>(ValueKey('key'));
+    final key = ValueNotifier<Key>(const ValueKey('key'));
     final itemScrollController = ItemScrollController();
 
     await tester.pumpWidget(
       MaterialApp(
         home: ValueListenableBuilder<Key>(
           valueListenable: key,
-          builder: (context, key, child) {
+          builder: (context, key, child) => ScrollablePositionedList.builder(
-            return ScrollablePositionedList.builder(
+            key: key,
-              key: key,
+            itemCount: 10,
-              itemCount: 10,
+            itemScrollController: itemScrollController,
-              itemScrollController: itemScrollController,
+            itemBuilder: (context, index) => SizedBox(
-              itemBuilder: (context, index) {
+              height: itemHeight,
-                return SizedBox(
+              child: Text('Item $index'),
-                  height: itemHeight,
+            ),
-                  child: Text('Item $index'),
+          ),
-                );
-              },
-            );
-          },
         ),
       ),
     );
 
     await tester.pumpAndSettle();
 
-    key.value = ValueKey('newKey');
+    key.value = const ValueKey('newKey');
     await tester.pumpAndSettle();
   });
 
@@ -2087,35 +2077,31 @@ void main() {
     tester.binding.window.devicePixelRatioTestValue = 1.0;
     tester.binding.window.physicalSizeTestValue =
         const Size(screenWidth, screenHeight);
-    final key = ValueNotifier<Key>(ValueKey('key'));
+    final key = ValueNotifier<Key>(const ValueKey('key'));
     final itemScrollController = ItemScrollController();
 
     await tester.pumpWidget(
       MaterialApp(
         home: ValueListenableBuilder<Key>(
           valueListenable: key,
-          builder: (context, key, child) {
+          builder: (context, key, child) => Container(
-            return Container(
+            key: key,
-              key: key,
+            child: ScrollablePositionedList.builder(
-              child: ScrollablePositionedList.builder(
+              itemCount: 100,
-                itemCount: 100,
+              itemScrollController: itemScrollController,
-                itemScrollController: itemScrollController,
+              itemBuilder: (context, index) => SizedBox(
-                itemBuilder: (context, index) {
+                height: itemHeight,
-                  return SizedBox(
+                child: Text('Item $index'),
-                    height: itemHeight,
-                    child: Text('Item $index'),
-                  );
-                },
               ),
-            );
+            ),
-          },
+          ),
         ),
       ),
     );
 
     await tester.pumpAndSettle();
 
-    key.value = ValueKey('newKey');
+    key.value = const ValueKey('newKey');
     await tester.pumpAndSettle();
 
     unawaited(
@@ -2130,7 +2116,7 @@ void main() {
     tester.binding.window.devicePixelRatioTestValue = 1.0;
     tester.binding.window.physicalSizeTestValue =
         const Size(screenWidth, screenHeight);
-    final containerKey = ValueNotifier<Key>(ValueKey('key'));
+    final containerKey = ValueNotifier<Key>(const ValueKey('key'));
     final scrollKey = GlobalKey();
     final itemScrollController = ItemScrollController();
 
@@ -2138,29 +2124,25 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<Key>(
           valueListenable: containerKey,
-          builder: (context, key, child) {
+          builder: (context, key, child) => Container(
-            return Container(
+            key: key,
-              key: key,
+            child: ScrollablePositionedList.builder(
-              child: ScrollablePositionedList.builder(
+              key: scrollKey,
-                key: scrollKey,
+              itemCount: 100,
-                itemCount: 100,
+              itemScrollController: itemScrollController,
-                itemScrollController: itemScrollController,
+              itemBuilder: (context, index) => SizedBox(
-                itemBuilder: (context, index) {
+                height: itemHeight,
-                  return SizedBox(
+                child: Text('Item $index'),
-                    height: itemHeight,
-                    child: Text('Item $index'),
-                  );
-                },
               ),
-            );
+            ),
-          },
+          ),
         ),
       ),
     );
 
     await tester.pumpAndSettle();
 
-    containerKey.value = ValueKey('newKey');
+    containerKey.value = const ValueKey('newKey');
     await tester.pumpAndSettle();
 
     unawaited(
@@ -2184,18 +2166,15 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<ItemScrollController>(
           valueListenable: itemScrollControllerListenable,
-          builder: (context, itemScrollController, child) {
+          builder: (context, itemScrollController, child) =>
-            return ScrollablePositionedList.builder(
+              ScrollablePositionedList.builder(
-              itemCount: 100,
+            itemCount: 100,
-              itemScrollController: itemScrollController,
+            itemScrollController: itemScrollController,
-              itemBuilder: (context, index) {
+            itemBuilder: (context, index) => SizedBox(
-                return SizedBox(
+              height: itemHeight,
-                  height: itemHeight,
+              child: Text('Item $index'),
-                  child: Text('Item $index'),
+            ),
-                );
+          ),
-              },
-            );
-          },
         ),
       ),
     );
@@ -2236,35 +2215,29 @@ void main() {
           Expanded(
             child: ValueListenableBuilder<ItemScrollController>(
               valueListenable: topItemScrollControllerListenable,
-              builder: (context, itemScrollController, child) {
+              builder: (context, itemScrollController, child) =>
-                return ScrollablePositionedList.builder(
+                  ScrollablePositionedList.builder(
-                  itemCount: 100,
+                itemCount: 100,
-                  itemScrollController: itemScrollController,
+                itemScrollController: itemScrollController,
-                  itemBuilder: (context, index) {
+                itemBuilder: (context, index) => SizedBox(
-                    return SizedBox(
+                  height: itemHeight,
-                      height: itemHeight,
+                  child: Text('Item $index'),
-                      child: Text('Item $index'),
+                ),
-                    );
+              ),
-                  },
-                );
-              },
             ),
           ),
           Expanded(
             child: ValueListenableBuilder<ItemScrollController>(
               valueListenable: bottomItemScrollControllerListenable,
-              builder: (context, itemScrollController, child) {
+              builder: (context, itemScrollController, child) =>
-                return ScrollablePositionedList.builder(
+                  ScrollablePositionedList.builder(
-                  itemCount: 100,
+                itemCount: 100,
-                  itemScrollController: itemScrollController,
+                itemScrollController: itemScrollController,
-                  itemBuilder: (context, index) {
+                itemBuilder: (context, index) => SizedBox(
-                    return SizedBox(
+                  height: itemHeight,
-                      height: itemHeight,
+                  child: Text('Item $index'),
-                      child: Text('Item $index'),
+                ),
-                    );
+              ),
-                  },
-                );
-              },
             ),
           ),
         ],

packages/stream_chat_flutter/test/src/scrollable_positioned_list/separated_scrollable_positioned_list_test.dart

@@ -270,7 +270,7 @@ void main() {
         initialAlignment: 0.5);
 
     unawaited(itemScrollController.scrollTo(
-        index: 16, duration: scrollDuration, alignment: 1.0));
+        index: 16, duration: scrollDuration, alignment: 1));
     await tester.pump();
     await tester.pump();
     await tester.pump(scrollDuration + scrollDurationTolerance);
@@ -477,7 +477,7 @@ void main() {
   });
 
   testWidgets('List can be keyed', (WidgetTester tester) async {
-    final key = ValueKey('key');
+    const key = ValueKey('key');
 
     await setUpWidgetTest(tester, key: key);
 
@@ -498,23 +498,20 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<int>(
           valueListenable: itemCount,
-          builder: (context, itemCount, child) {
+          builder: (context, itemCount, child) =>
-            return ScrollablePositionedList.separated(
+              ScrollablePositionedList.separated(
-              initialScrollIndex: 0,
+            itemCount: itemCount,
-              initialAlignment: 0,
+            itemScrollController: itemScrollController,
-              itemCount: itemCount,
+            itemPositionsListener: itemPositionsListener,
-              itemScrollController: itemScrollController,
+            itemBuilder: (context, index) => SizedBox(
-              itemPositionsListener: itemPositionsListener,
+              height: itemHeight,
-              itemBuilder: (context, index) => SizedBox(
+              child: Text('Item $index'),
-                height: itemHeight,
+            ),
-                child: Text('Item $index'),
+            separatorBuilder: (context, index) => SizedBox(
-              ),
+              height: separatorHeight,
-              separatorBuilder: (context, index) => SizedBox(
+              child: Text('Separator $index'),
-                height: separatorHeight,
+            ),
-                child: Text('Separator $index'),
+          ),
-              ),
-            );
-          },
         ),
       ),
     );
@@ -542,23 +539,20 @@ void main() {
       MaterialApp(
         home: ValueListenableBuilder<int>(
           valueListenable: itemCount,
-          builder: (context, itemCount, child) {
+          builder: (context, itemCount, child) =>
-            return ScrollablePositionedList.separated(
+              ScrollablePositionedList.separated(
-              initialScrollIndex: 0,
+            itemCount: itemCount,
-              initialAlignment: 0,
+            itemScrollController: itemScrollController,
-              itemCount: itemCount,
+            itemPositionsListener: itemPositionsListener,
-              itemScrollController: itemScrollController,
+            itemBuilder: (context, index) => SizedBox(
-              itemPositionsListener: itemPositionsListener,
+              height: itemHeight,
-              itemBuilder: (context, index) => SizedBox(
+              child: Text('Item $index'),
-                height: itemHeight,
+            ),
-                child: Text('Item $index'),
+            separatorBuilder: (context, index) => SizedBox(
-              ),
+              height: separatorHeight,
-              separatorBuilder: (context, index) => SizedBox(
+              child: Text('Separator $index'),
-                height: separatorHeight,
+            ),
-                child: Text('Separator $index'),
+          ),
-              ),
-            );
-          },
         ),
       ),
     );