moved scroll function out of scaling gesture detector

lib/widgets/album/grid/list_section_layout.dart

@@ -89,11 +89,14 @@ class SectionedListLayoutProvider extends StatelessWidget {
 
     final minEntryIndex = sectionChildIndex * columnCount;
     final maxEntryIndex = min(sectionEntryCount, minEntryIndex + columnCount);
+    final ids = <int>[];
     final children = <Widget>[];
     for (var i = minEntryIndex; i < maxEntryIndex; i++) {
       final entry = section[i];
+      final id = entry.contentId;
+      ids.add(id);
       children.add(GridThumbnail(
-        key: ValueKey(entry.contentId),
+        key: ValueKey(id),
         collection: collection,
         index: i,
         entry: entry,
@@ -101,6 +104,7 @@ class SectionedListLayoutProvider extends StatelessWidget {
       ));
     }
     return Row(
+      key: ValueKey(ids.join('-')),
       mainAxisSize: MainAxisSize.min,
       children: children,
     );
@@ -136,7 +140,6 @@ class SectionedListLayout {
 
     final left = tileExtent * column;
     final top = sectionLayout.indexToLayoutOffset(listIndex);
-    debugPrint('TLAD getTileRect sectionKey=$sectionKey sectionOffset=${sectionLayout.minOffset} top=$top row=$row column=$column for title=${entry.bestTitle}');
     return Rect.fromLTWH(left, top, tileExtent, tileExtent);
   }
 }

lib/widgets/album/grid/scaling.dart

@@ -2,29 +2,27 @@ import 'dart:math';
 import 'dart:ui' as ui;
 
 import 'package:aves/model/image_entry.dart';
-import 'package:aves/widgets/album/grid/list_section_layout.dart';
 import 'package:aves/widgets/album/grid/list_sliver.dart';
 import 'package:aves/widgets/album/grid/tile_extent_manager.dart';
 import 'package:aves/widgets/album/thumbnail/decorated.dart';
 import 'package:aves/widgets/common/data_providers/media_query_data_provider.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
-import 'package:provider/provider.dart';
 
 class GridScaleGestureDetector extends StatefulWidget {
   final GlobalKey scrollableKey;
-  final ValueNotifier<double> appBarHeightNotifier;
   final ValueNotifier<double> extentNotifier;
   final Size mqSize;
   final double mqHorizontalPadding;
+  final void Function(ImageEntry entry) onScaled;
   final Widget child;
 
   const GridScaleGestureDetector({
     this.scrollableKey,
-    @required this.appBarHeightNotifier,
     @required this.extentNotifier,
     @required this.mqSize,
     @required this.mqHorizontalPadding,
+    @required this.onScaled,
     @required this.child,
   });
 
@@ -38,7 +36,6 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
   ValueNotifier<double> _scaledExtentNotifier;
   OverlayEntry _overlayEntry;
   ThumbnailMetadata _metadata;
-  RenderViewport _renderViewport;
 
   ValueNotifier<double> get tileExtentNotifier => widget.extentNotifier;
 
@@ -64,7 +61,6 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
         final renderMetaData = firstOf<RenderMetaData>(result);
         // abort if we cannot find an image to show on overlay
         if (renderMetaData == null) return;
-        _renderViewport = firstOf<RenderViewport>(result);
         _metadata = renderMetaData.metaData;
         _startExtent = tileExtentNotifier.value;
         _scaledExtentNotifier = ValueNotifier(_startExtent);
@@ -113,21 +109,8 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
           _applyingScale = false;
         } else {
           // scroll to show the focal point thumbnail at its new position
-          final viewportClosure = _renderViewport;
           WidgetsBinding.instance.addPostFrameCallback((_) {
-            // about scrolling & offset retrieval:
+            widget.onScaled(_metadata.entry);
-            // `Scrollable.ensureVisible` only works on already rendered objects
-            // `RenderViewport.showOnScreen` can find any `RenderSliver`, but not always a `RenderMetadata`
-            // `RenderViewport.scrollOffsetOf` is a good alternative
-            final scrollableContext = widget.scrollableKey.currentContext;
-            final gridSize = (scrollableContext.findRenderObject() as RenderBox).size;
-            final sectionLayout = Provider.of<SectionedListLayout>(context, listen: false);
-            final tileRect = sectionLayout.getTileRect(_metadata.entry) ?? Rect.zero;
-            // most of the time the app bar will be scrolled away after scaling,
-            // so we compensate for it to center the focal point thumbnail
-            final appBarHeight = widget.appBarHeightNotifier.value;
-            final scrollOffset = tileRect.top + (tileRect.height - gridSize.height) / 2 + appBarHeight;
-            viewportClosure.offset.jumpTo(max(.0, scrollOffset));
             _applyingScale = false;
           });
         }

lib/widgets/album/thumbnail_collection.dart

@@ -1,6 +1,9 @@
+import 'dart:math';
+
 import 'package:aves/model/collection_lens.dart';
 import 'package:aves/model/filters/favourite.dart';
 import 'package:aves/model/filters/mime.dart';
+import 'package:aves/model/image_entry.dart';
 import 'package:aves/model/mime_types.dart';
 import 'package:aves/widgets/album/app_bar.dart';
 import 'package:aves/widgets/album/empty.dart';
@@ -18,7 +21,6 @@ import 'package:tuple/tuple.dart';
 class ThumbnailCollection extends StatelessWidget {
   final ValueNotifier<double> _appBarHeightNotifier = ValueNotifier(0);
   final ValueNotifier<double> _tileExtentNotifier = ValueNotifier(0);
-  final GlobalKey _scrollableKey = GlobalKey();
 
   @override
   Widget build(BuildContext context) {
@@ -34,23 +36,25 @@ class ThumbnailCollection extends StatelessWidget {
           // so that view updates on collection filter changes
           return Consumer<CollectionLens>(
             builder: (context, collection, child) {
-              final scrollView = _buildScrollView(collection);
+              final appBar = CollectionAppBar(
-              final draggable = _buildDraggableScrollView(scrollView);
-              final scaler = GridScaleGestureDetector(
-                scrollableKey: _scrollableKey,
                 appBarHeightNotifier: _appBarHeightNotifier,
-                extentNotifier: _tileExtentNotifier,
+                collection: collection,
-                mqSize: mqSize,
-                mqHorizontalPadding: mqHorizontalPadding,
-                child: draggable,
               );
+
               final sectionedListLayoutProvider = ValueListenableBuilder<double>(
                 valueListenable: _tileExtentNotifier,
                 builder: (context, tileExtent, child) => SectionedListLayoutProvider(
                   collection: collection,
                   scrollableWidth: mqSize.width - mqHorizontalPadding,
                   tileExtent: tileExtent,
-                  child: scaler,
+                  child: _ScalableThumbnailCollection(
+                    appBarHeightNotifier: _appBarHeightNotifier,
+                    tileExtentNotifier: _tileExtentNotifier,
+                    collection: collection,
+                    mqSize: mqSize,
+                    mqHorizontalPadding: mqHorizontalPadding,
+                    appBar: appBar,
+                  ),
                 ),
               );
               return sectionedListLayoutProvider;
@@ -60,8 +64,42 @@ class ThumbnailCollection extends StatelessWidget {
       ),
     );
   }
+}
 
-  ScrollView _buildScrollView(CollectionLens collection) {
+class _ScalableThumbnailCollection extends StatelessWidget {
+  final CollectionLens collection;
+  final ValueNotifier<double> appBarHeightNotifier;
+  final ValueNotifier<double> tileExtentNotifier;
+  final Size mqSize;
+  final double mqHorizontalPadding;
+  final Widget appBar;
+
+  final GlobalKey _scrollableKey = GlobalKey();
+
+  _ScalableThumbnailCollection({
+    @required this.appBarHeightNotifier,
+    @required this.tileExtentNotifier,
+    @required this.collection,
+    @required this.mqSize,
+    @required this.mqHorizontalPadding,
+    @required this.appBar,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final scrollView = _buildScrollView(appBar, collection);
+    final draggable = _buildDraggableScrollView(scrollView);
+    return GridScaleGestureDetector(
+      scrollableKey: _scrollableKey,
+      extentNotifier: tileExtentNotifier,
+      mqSize: mqSize,
+      mqHorizontalPadding: mqHorizontalPadding,
+      onScaled: (entry) => _scrollToEntry(context, entry),
+      child: draggable,
+    );
+  }
+
+  ScrollView _buildScrollView(Widget appBar, CollectionLens collection) {
     return CustomScrollView(
       key: _scrollableKey,
       primary: true,
@@ -69,10 +107,7 @@ class ThumbnailCollection extends StatelessWidget {
       // when there is no content and we use `SliverFillRemaining`
       physics: collection.isEmpty ? const NeverScrollableScrollPhysics() : null,
       slivers: [
-        CollectionAppBar(
+      appBar,
-          appBarHeightNotifier: _appBarHeightNotifier,
-          collection: collection,
-        ),
         collection.isEmpty
             ? SliverFillRemaining(
                 child: _buildEmptyCollectionPlaceholder(collection),
@@ -93,7 +128,7 @@ class ThumbnailCollection extends StatelessWidget {
 
   Widget _buildDraggableScrollView(ScrollView scrollView) {
     return ValueListenableBuilder<double>(
-      valueListenable: _appBarHeightNotifier,
+      valueListenable: appBarHeightNotifier,
       builder: (context, appBarHeight, child) => Selector<MediaQueryData, double>(
         selector: (context, mq) => mq.viewInsets.bottom,
         builder: (context, mqViewInsetsBottom, child) => DraggableScrollbar(
@@ -128,4 +163,21 @@ class ThumbnailCollection extends StatelessWidget {
               )
             : const EmptyContent();
   }
+
+  // about scrolling & offset retrieval:
+  // `Scrollable.ensureVisible` only works on already rendered objects
+  // `RenderViewport.showOnScreen` can find any `RenderSliver`, but not always a `RenderMetadata`
+  // `RenderViewport.scrollOffsetOf` is a good alternative
+  void _scrollToEntry(BuildContext context, ImageEntry entry) {
+    final scrollableContext = _scrollableKey.currentContext;
+    final scrollableHeight = (scrollableContext.findRenderObject() as RenderBox).size.height;
+    final sectionLayout = Provider.of<SectionedListLayout>(context, listen: false);
+    final tileRect = sectionLayout.getTileRect(entry) ?? Rect.zero;
+    // most of the time the app bar will be scrolled away after scaling,
+    // so we compensate for it to center the focal point thumbnail
+    final appBarHeight = appBarHeightNotifier.value;
+    final scrollOffset = tileRect.top + (tileRect.height - scrollableHeight) / 2 + appBarHeight;
+
+    PrimaryScrollController.of(context)?.jumpTo(max(.0, scrollOffset));
+  }
 }