custom SliverList to avoid performing layout on children

lib/labs/sliver_known_extent_list.dart

@@ -0,0 +1,252 @@
+import 'dart:math' as math;
+
+import 'package:aves/widgets/album/collection_list_sliver.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+class SliverKnownExtentList extends SliverMultiBoxAdaptorWidget {
+  final List<SectionLayout> sectionLayouts;
+
+  const SliverKnownExtentList({
+    Key key,
+    @required SliverChildDelegate delegate,
+    @required this.sectionLayouts,
+  }) : super(key: key, delegate: delegate);
+
+  @override
+  RenderSliverKnownExtentBoxAdaptor createRenderObject(BuildContext context) {
+    final element = context as SliverMultiBoxAdaptorElement;
+    return RenderSliverKnownExtentBoxAdaptor(childManager: element, sectionLayouts: sectionLayouts);
+  }
+
+  @override
+  void updateRenderObject(BuildContext context, RenderSliverKnownExtentBoxAdaptor renderObject) {
+    renderObject.sectionLayouts = sectionLayouts;
+  }
+}
+
+class RenderSliverKnownExtentBoxAdaptor extends RenderSliverMultiBoxAdaptor {
+  List<SectionLayout> _sectionLayouts;
+
+  List<SectionLayout> get sectionLayouts => _sectionLayouts;
+
+  set sectionLayouts(List<SectionLayout> value) {
+    assert(value != null);
+    if (_sectionLayouts == value) return;
+    _sectionLayouts = value;
+    markNeedsLayout();
+  }
+
+  RenderSliverKnownExtentBoxAdaptor({
+    @required RenderSliverBoxChildManager childManager,
+    @required List<SectionLayout> sectionLayouts,
+  })  : _sectionLayouts = sectionLayouts,
+        super(childManager: childManager);
+
+  SectionLayout sectionAtIndex(int index) => sectionLayouts.firstWhere((section) => section.hasChild(index), orElse: () => null);
+
+  SectionLayout sectionAtOffset(double scrollOffset) => sectionLayouts.firstWhere((section) => section.hasChildAtOffset(scrollOffset), orElse: () => null);
+
+  double indexToLayoutOffset(int index) {
+    return sectionAtIndex(index).indexToLayoutOffset(index);
+  }
+
+  int getMinChildIndexForScrollOffset(double scrollOffset) {
+    return sectionAtOffset(scrollOffset).getMinChildIndexForScrollOffset(scrollOffset);
+  }
+
+  int getMaxChildIndexForScrollOffset(double scrollOffset) {
+    return (sectionAtOffset(scrollOffset) ?? sectionLayouts.last).getMaxChildIndexForScrollOffset(scrollOffset);
+  }
+
+  double estimateMaxScrollOffset(
+    SliverConstraints constraints, {
+    int firstIndex,
+    int lastIndex,
+    double leadingScrollOffset,
+    double trailingScrollOffset,
+  }) {
+    return childManager.estimateMaxScrollOffset(
+      constraints,
+      firstIndex: firstIndex,
+      lastIndex: lastIndex,
+      leadingScrollOffset: leadingScrollOffset,
+      trailingScrollOffset: trailingScrollOffset,
+    );
+  }
+
+  double computeMaxScrollOffset(SliverConstraints constraints) {
+    return sectionLayouts.last.maxOffset;
+  }
+
+  int _calculateLeadingGarbage(int firstIndex) {
+    var walker = firstChild;
+    var leadingGarbage = 0;
+    while (walker != null && indexOf(walker) < firstIndex) {
+      leadingGarbage += 1;
+      walker = childAfter(walker);
+    }
+    return leadingGarbage;
+  }
+
+  int _calculateTrailingGarbage(int targetLastIndex) {
+    var walker = lastChild;
+    var trailingGarbage = 0;
+    while (walker != null && indexOf(walker) > targetLastIndex) {
+      trailingGarbage += 1;
+      walker = childBefore(walker);
+    }
+    return trailingGarbage;
+  }
+
+  @override
+  void performLayout() {
+    final constraints = this.constraints;
+    childManager.didStartLayout();
+    childManager.setDidUnderflow(false);
+
+    final scrollOffset = constraints.scrollOffset + constraints.cacheOrigin;
+    assert(scrollOffset >= 0.0);
+    final remainingExtent = constraints.remainingCacheExtent;
+    assert(remainingExtent >= 0.0);
+    final targetEndScrollOffset = scrollOffset + remainingExtent;
+
+    final childConstraints = constraints.asBoxConstraints();
+
+    final firstIndex = getMinChildIndexForScrollOffset(scrollOffset);
+    final targetLastIndex = targetEndScrollOffset.isFinite ? getMaxChildIndexForScrollOffset(targetEndScrollOffset) : null;
+
+    if (firstChild != null) {
+      final leadingGarbage = _calculateLeadingGarbage(firstIndex);
+      final trailingGarbage = _calculateTrailingGarbage(targetLastIndex);
+      collectGarbage(leadingGarbage, trailingGarbage);
+    } else {
+      collectGarbage(0, 0);
+    }
+
+    if (firstChild == null) {
+      if (!addInitialChild(index: firstIndex, layoutOffset: indexToLayoutOffset(firstIndex))) {
+        // There are either no children, or we are past the end of all our children.
+        // If it is the latter, we will need to find the first available child.
+        double max;
+        if (childManager.childCount != null) {
+          max = computeMaxScrollOffset(constraints);
+        } else if (firstIndex <= 0) {
+          max = 0.0;
+        } else {
+          // We will have to find it manually.
+          var possibleFirstIndex = firstIndex - 1;
+          while (possibleFirstIndex > 0 &&
+              !addInitialChild(
+                index: possibleFirstIndex,
+                layoutOffset: indexToLayoutOffset(possibleFirstIndex),
+              )) {
+            possibleFirstIndex -= 1;
+          }
+          max = sectionAtIndex(possibleFirstIndex).indexToLayoutOffset(possibleFirstIndex);
+        }
+        geometry = SliverGeometry(
+          scrollExtent: max,
+          maxPaintExtent: max,
+        );
+        childManager.didFinishLayout();
+        return;
+      }
+    }
+
+    RenderBox trailingChildWithLayout;
+
+    for (var index = indexOf(firstChild) - 1; index >= firstIndex; --index) {
+      final child = insertAndLayoutLeadingChild(childConstraints);
+      if (child == null) {
+        // Items before the previously first child are no longer present.
+        // Reset the scroll offset to offset all items prior and up to the
+        // missing item. Let parent re-layout everything.
+        final layout = sectionAtIndex(index) ?? sectionLayouts.first;
+        geometry = SliverGeometry(scrollOffsetCorrection: layout.indexToMaxScrollOffset(index));
+        return;
+      }
+      final childParentData = child.parentData as SliverMultiBoxAdaptorParentData;
+      childParentData.layoutOffset = indexToLayoutOffset(index);
+      assert(childParentData.index == index);
+      trailingChildWithLayout ??= child;
+    }
+
+    if (trailingChildWithLayout == null) {
+      firstChild.layout(childConstraints);
+      final childParentData = firstChild.parentData as SliverMultiBoxAdaptorParentData;
+      childParentData.layoutOffset = indexToLayoutOffset(firstIndex);
+      trailingChildWithLayout = firstChild;
+    }
+
+    var estimatedMaxScrollOffset = double.infinity;
+    for (var index = indexOf(trailingChildWithLayout) + 1; targetLastIndex == null || index <= targetLastIndex; ++index) {
+      var child = childAfter(trailingChildWithLayout);
+      if (child == null || indexOf(child) != index) {
+        child = insertAndLayoutChild(childConstraints, after: trailingChildWithLayout);
+        if (child == null) {
+          // We have run out of children.
+          final layout = sectionAtIndex(index) ?? sectionLayouts.last;
+          estimatedMaxScrollOffset = layout.indexToMaxScrollOffset(index);
+          break;
+        }
+      } else {
+        child.layout(childConstraints);
+      }
+      trailingChildWithLayout = child;
+      assert(child != null);
+      final childParentData = child.parentData as SliverMultiBoxAdaptorParentData;
+      assert(childParentData.index == index);
+      childParentData.layoutOffset = indexToLayoutOffset(childParentData.index);
+    }
+
+    final lastIndex = indexOf(lastChild);
+    final leadingScrollOffset = indexToLayoutOffset(firstIndex);
+    final trailingScrollOffset = indexToLayoutOffset(lastIndex + 1);
+
+    assert(firstIndex == 0 || childScrollOffset(firstChild) - scrollOffset <= precisionErrorTolerance);
+    assert(debugAssertChildListIsNonEmptyAndContiguous());
+    assert(indexOf(firstChild) == firstIndex);
+    assert(targetLastIndex == null || lastIndex <= targetLastIndex);
+
+    estimatedMaxScrollOffset = math.min(
+      estimatedMaxScrollOffset,
+      estimateMaxScrollOffset(
+        constraints,
+        firstIndex: firstIndex,
+        lastIndex: lastIndex,
+        leadingScrollOffset: leadingScrollOffset,
+        trailingScrollOffset: trailingScrollOffset,
+      ),
+    );
+
+    final paintExtent = calculatePaintOffset(
+      constraints,
+      from: leadingScrollOffset,
+      to: trailingScrollOffset,
+    );
+
+    final cacheExtent = calculateCacheOffset(
+      constraints,
+      from: leadingScrollOffset,
+      to: trailingScrollOffset,
+    );
+
+    final targetEndScrollOffsetForPaint = constraints.scrollOffset + constraints.remainingPaintExtent;
+    final targetLastIndexForPaint = targetEndScrollOffsetForPaint.isFinite ? getMaxChildIndexForScrollOffset(targetEndScrollOffsetForPaint) : null;
+    geometry = SliverGeometry(
+      scrollExtent: estimatedMaxScrollOffset,
+      paintExtent: paintExtent,
+      cacheExtent: cacheExtent,
+      maxPaintExtent: estimatedMaxScrollOffset,
+      // Conservative to avoid flickering away the clip during scroll.
+      hasVisualOverflow: (targetLastIndexForPaint != null && lastIndex >= targetLastIndexForPaint) || constraints.scrollOffset > 0.0,
+    );
+
+    // We may have started the layout while scrolled to the end, which would not
+    // expose a new child.
+    if (estimatedMaxScrollOffset == trailingScrollOffset) childManager.setDidUnderflow(true);
+    childManager.didFinishLayout();
+  }
+}

lib/model/collection_lens.dart

@@ -162,10 +162,9 @@ class CollectionLens with ChangeNotifier {
         break;
       case SortFactor.name:
         final byAlbum = groupBy(_filteredEntries, (ImageEntry entry) => entry.directory);
-        final albums = byAlbum.keys.toSet();
         final compare = (a, b) {
-          final ua = CollectionSource.getUniqueAlbumName(a, albums);
-          final ub = CollectionSource.getUniqueAlbumName(b, albums);
+          final ua = source.getUniqueAlbumName(a);
+          final ub = source.getUniqueAlbumName(b);
           return compareAsciiUpperCase(ua, ub);
         };
         sections = Map.unmodifiable(SplayTreeMap.of(byAlbum, compare));

lib/model/collection_source.dart

@@ -8,6 +8,7 @@ import 'package:path/path.dart';
 
 class CollectionSource {
   final List<ImageEntry> _rawEntries;
+  final Set<String> _folderPaths = {};
   final EventBus _eventBus = EventBus();
 
   List<String> sortedAlbums = List.unmodifiable(const Iterable.empty());
@@ -106,11 +107,10 @@ class CollectionSource {
   }
 
   void updateAlbums() {
-    final albums = _rawEntries.map((entry) => entry.directory).toSet();
-    final sorted = albums.toList()
+    final sorted = _folderPaths.toList()
       ..sort((a, b) {
-        final ua = getUniqueAlbumName(a, albums);
-        final ub = getUniqueAlbumName(b, albums);
+        final ua = getUniqueAlbumName(a);
+        final ub = getUniqueAlbumName(b);
         return compareAsciiUpperCase(ua, ub);
       });
     sortedAlbums = List.unmodifiable(sorted);
@@ -134,6 +134,7 @@ class CollectionSource {
       entry.catalogDateMillis = savedDates.firstWhere((metadata) => metadata.contentId == contentId, orElse: () => null)?.dateMillis;
     });
     _rawEntries.addAll(entries);
+    _folderPaths.addAll(_rawEntries.map((entry) => entry.directory).toSet());
     eventBus.fire(const EntryAddedEvent());
   }
 
@@ -146,8 +147,8 @@ class CollectionSource {
     return success;
   }
 
-  static String getUniqueAlbumName(String album, Iterable<String> albums) {
-    final otherAlbums = albums?.where((item) => item != album) ?? [];
+  String getUniqueAlbumName(String album) {
+    final otherAlbums = _folderPaths.where((item) => item != album);
     final parts = album.split(separator);
     var partCount = 0;
     String testName;

lib/widgets/album/collection_drawer.dart

@@ -5,8 +5,8 @@ import 'package:aves/model/collection_source.dart';
 import 'package:aves/model/filters/album.dart';
 import 'package:aves/model/filters/favourite.dart';
 import 'package:aves/model/filters/filters.dart';
-import 'package:aves/model/filters/mime.dart';
 import 'package:aves/model/filters/location.dart';
+import 'package:aves/model/filters/mime.dart';
 import 'package:aves/model/filters/tag.dart';
 import 'package:aves/model/mime_types.dart';
 import 'package:aves/model/settings.dart';
@@ -96,9 +96,9 @@ class _CollectionDrawerState extends State<CollectionDrawer> {
     final buildAlbumEntry = (album) => _FilteredCollectionNavTile(
           source: source,
           leading: IconUtils.getAlbumIcon(context: context, album: album),
-          title: CollectionSource.getUniqueAlbumName(album, source.sortedAlbums),
+          title: source.getUniqueAlbumName(album),
           dense: true,
-          filter: AlbumFilter(album, CollectionSource.getUniqueAlbumName(album, source.sortedAlbums)),
+          filter: AlbumFilter(album, source.getUniqueAlbumName(album)),
         );
     final buildTagEntry = (tag) => _FilteredCollectionNavTile(
           source: source,

lib/widgets/album/collection_list_sliver.dart

@@ -1,8 +1,12 @@
 import 'dart:math';
 
+import 'package:aves/labs/sliver_known_extent_list.dart';
 import 'package:aves/model/collection_lens.dart';
+import 'package:aves/utils/constants.dart';
 import 'package:aves/widgets/album/collection_section.dart';
+import 'package:aves/widgets/album/grid/header_generic.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 
 // use a `SliverList` instead of multiple `SliverGrid` because having one `SliverGrid` per section does not scale up
 // with the multiple `SliverGrid` solution, thumbnails at the beginning of each sections are built even though they are offscreen
@@ -10,33 +14,56 @@ import 'package:flutter/material.dart';
 class CollectionListSliver extends StatelessWidget {
   final CollectionLens collection;
   final bool showHeader;
+  final double scrollableWidth;
   final int columnCount;
   final double tileExtent;
 
-  const CollectionListSliver({
+  CollectionListSliver({
     Key key,
     @required this.collection,
     @required this.showHeader,
-    @required this.columnCount,
+    @required this.scrollableWidth,
     @required this.tileExtent,
-  }) : super(key: key);
+  })  : columnCount = (scrollableWidth / tileExtent).round(),
+        super(key: key);
 
   @override
   Widget build(BuildContext context) {
-    final sectionLayouts = <_SectionLayout>[];
+    final sectionLayouts = <SectionLayout>[];
     final sectionKeys = collection.sections.keys.toList();
-    var firstIndex = 0;
+    final headerPadding = TitleSectionHeader.padding;
+    var currentIndex = 0, currentOffset = 0.0;
     sectionKeys.forEach((sectionKey) {
       final sectionEntryCount = collection.sections[sectionKey].length;
-      final rowCount = (sectionEntryCount / columnCount).ceil();
-      final widgetCount = rowCount + (showHeader ? 1 : 0);
-      // closure of `firstIndex` on `sectionFirstIndex`
-      final sectionFirstIndex = firstIndex;
+      final sectionChildCount = 1 + (sectionEntryCount / columnCount).ceil();
+
+      var headerExtent = 0.0;
+      if (showHeader) {
+        // only compute height for album headers, as they're the only likely ones to split on multiple lines
+        if (sectionKey is String) {
+          final text = collection.source.getUniqueAlbumName(sectionKey);
+          headerExtent = SectionLayout.computeHeaderExtent(text, scrollableWidth - headerPadding.horizontal);
+        }
+        headerExtent = max(headerExtent, TitleSectionHeader.leadingDimension) + headerPadding.vertical;
+      }
+
+      final sectionFirstIndex = currentIndex;
+      currentIndex += sectionChildCount;
+      final sectionLastIndex = currentIndex - 1;
+
+      final sectionMinOffset = currentOffset;
+      currentOffset += headerExtent + tileExtent * (sectionChildCount - 1);
+      final sectionMaxOffset = currentOffset;
+
       sectionLayouts.add(
-        _SectionLayout(
+        SectionLayout(
           sectionKey: sectionKey,
-          widgetCount: widgetCount,
           firstIndex: sectionFirstIndex,
+          lastIndex: sectionLastIndex,
+          minOffset: sectionMinOffset,
+          maxOffset: sectionMaxOffset,
+          headerExtent: headerExtent,
+          tileExtent: tileExtent,
           builder: (context, listIndex) {
             listIndex -= sectionFirstIndex;
             if (showHeader) {
@@ -69,16 +96,16 @@ class CollectionListSliver extends StatelessWidget {
           },
         ),
       );
-      firstIndex += widgetCount;
     });
-    final childCount = firstIndex;
+    final childCount = currentIndex;
 
-    return SliverList(
+    return SliverKnownExtentList(
+      sectionLayouts: sectionLayouts,
       delegate: SliverChildBuilderDelegate(
         (context, index) {
           if (index >= childCount) return null;
-          final sectionLayout = sectionLayouts.firstWhere((section) => section.hasChild(index));
-          return sectionLayout.builder(context, index);
+          final sectionLayout = sectionLayouts.firstWhere((section) => section.hasChild(index), orElse: () => null);
+          return sectionLayout?.builder(context, index) ?? const SizedBox.shrink();
         },
         childCount: childCount,
         addAutomaticKeepAlives: false,
@@ -87,19 +114,55 @@ class CollectionListSliver extends StatelessWidget {
   }
 }
 
-class _SectionLayout {
+class SectionLayout {
   final dynamic sectionKey;
-  final int widgetCount;
-  final int firstIndex;
-  final int lastIndex;
+  final int firstIndex, lastIndex;
+  final double minOffset, maxOffset;
+  final double headerExtent, tileExtent;
   final IndexedWidgetBuilder builder;
 
-  const _SectionLayout({
+  const SectionLayout({
     @required this.sectionKey,
-    @required this.widgetCount,
     @required this.firstIndex,
+    @required this.lastIndex,
+    @required this.minOffset,
+    @required this.maxOffset,
+    @required this.headerExtent,
+    @required this.tileExtent,
     @required this.builder,
-  }) : lastIndex = firstIndex + widgetCount - 1;
+  });
 
   bool hasChild(int index) => firstIndex <= index && index <= lastIndex;
+
+  bool hasChildAtOffset(double scrollOffset) => minOffset <= scrollOffset && scrollOffset <= maxOffset;
+
+  double indexToLayoutOffset(int index) {
+    return minOffset + (index == firstIndex ? 0 : headerExtent + (index - firstIndex - 1) * tileExtent);
+  }
+
+  double indexToMaxScrollOffset(int index) {
+    return minOffset + headerExtent + (index - firstIndex) * tileExtent;
+  }
+
+  int getMinChildIndexForScrollOffset(double scrollOffset) {
+    scrollOffset -= minOffset + headerExtent;
+    return firstIndex + (scrollOffset < 0 ? 0 : (scrollOffset / tileExtent).floor());
+  }
+
+  int getMaxChildIndexForScrollOffset(double scrollOffset) {
+    scrollOffset -= minOffset + headerExtent;
+    return firstIndex + (scrollOffset < 0 ? 0 : (scrollOffset / tileExtent).ceil() - 1);
+  }
+
+  // TODO TLAD cache header extent computation?
+  static double computeHeaderExtent(String text, double scrollableWidth) {
+    final para = RenderParagraph(
+      TextSpan(
+        text: text,
+        style: Constants.titleTextStyle,
+      ),
+      textDirection: TextDirection.ltr,
+    )..layout(BoxConstraints(maxWidth: scrollableWidth), parentUsesSize: true);
+    return para.getMaxIntrinsicHeight(scrollableWidth);
+  }
 }

lib/widgets/album/collection_section.dart

@@ -1,10 +1,8 @@
 import 'package:aves/model/collection_lens.dart';
-import 'package:aves/model/collection_source.dart';
 import 'package:aves/model/image_entry.dart';
-import 'package:aves/widgets/album/sections.dart';
+import 'package:aves/widgets/album/grid/header_album.dart';
 import 'package:aves/widgets/album/thumbnail.dart';
 import 'package:aves/widgets/album/transparent_material_page_route.dart';
-import 'package:aves/widgets/common/icons.dart';
 import 'package:aves/widgets/fullscreen/fullscreen_page.dart';
 import 'package:flutter/material.dart';
 
@@ -60,67 +58,3 @@ class ThumbnailMetadata {
 
   const ThumbnailMetadata(this.index, this.entry);
 }
-
-class SectionHeader extends StatelessWidget {
-  final CollectionLens collection;
-  final Map<dynamic, List<ImageEntry>> sections;
-  final dynamic sectionKey;
-
-  const SectionHeader({
-    Key key,
-    @required this.collection,
-    @required this.sections,
-    @required this.sectionKey,
-  }) : super(key: key);
-
-  @override
-  Widget build(BuildContext context) {
-    Widget header;
-    switch (collection.sortFactor) {
-      case SortFactor.date:
-        if (collection.sortFactor == SortFactor.date) {
-          switch (collection.groupFactor) {
-            case GroupFactor.album:
-              header = _buildAlbumSectionHeader(context);
-              break;
-            case GroupFactor.month:
-              header = MonthSectionHeader(key: ValueKey(sectionKey), date: sectionKey as DateTime);
-              break;
-            case GroupFactor.day:
-              header = DaySectionHeader(key: ValueKey(sectionKey), date: sectionKey as DateTime);
-              break;
-          }
-        }
-        break;
-      case SortFactor.size:
-        break;
-      case SortFactor.name:
-        header = _buildAlbumSectionHeader(context);
-        break;
-    }
-    return header != null
-        ? IgnorePointer(
-            child: header,
-          )
-        : const SizedBox.shrink();
-  }
-
-  Widget _buildAlbumSectionHeader(BuildContext context) {
-    var albumIcon = IconUtils.getAlbumIcon(context: context, album: sectionKey as String);
-    if (albumIcon != null) {
-      albumIcon = Material(
-        type: MaterialType.circle,
-        elevation: 3,
-        color: Colors.transparent,
-        shadowColor: Colors.black,
-        child: albumIcon,
-      );
-    }
-    final title = CollectionSource.getUniqueAlbumName(sectionKey as String, sections.keys.cast<String>());
-    return TitleSectionHeader(
-      key: ValueKey(title),
-      leading: albumIcon,
-      title: title,
-    );
-  }
-}

lib/widgets/album/grid/header_album.dart

@@ -0,0 +1,31 @@
+import 'package:aves/widgets/album/grid/header_generic.dart';
+import 'package:aves/widgets/common/icons.dart';
+import 'package:flutter/material.dart';
+
+class AlbumSectionHeader extends StatelessWidget {
+  final String folderPath, albumName;
+
+  const AlbumSectionHeader({
+    Key key,
+    @required this.folderPath,
+    @required this.albumName,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    var albumIcon = IconUtils.getAlbumIcon(context: context, album: folderPath);
+    if (albumIcon != null) {
+      albumIcon = Material(
+        type: MaterialType.circle,
+        elevation: 3,
+        color: Colors.transparent,
+        shadowColor: Colors.black,
+        child: albumIcon,
+      );
+    }
+    return TitleSectionHeader(
+      leading: albumIcon,
+      title: albumName,
+    );
+  }
+}

lib/widgets/album/grid/header_date.dart

@@ -1,6 +1,5 @@
-import 'package:aves/utils/constants.dart';
 import 'package:aves/utils/time_utils.dart';
-import 'package:aves/widgets/common/fx/outlined_text.dart';
+import 'package:aves/widgets/album/grid/header_generic.dart';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
 
@@ -48,33 +47,3 @@ class MonthSectionHeader extends StatelessWidget {
     return TitleSectionHeader(title: text);
   }
 }
-
-class TitleSectionHeader extends StatelessWidget {
-  final Widget leading;
-  final String title;
-
-  const TitleSectionHeader({Key key, this.leading, this.title}) : super(key: key);
-
-  static const leadingDimension = 32.0;
-  static const leadingPadding = EdgeInsets.only(right: 8, bottom: 4);
-
-  @override
-  Widget build(BuildContext context) {
-    return Padding(
-      padding: const EdgeInsets.all(16),
-      child: OutlinedText(
-        leadingBuilder: leading != null
-            ? (context, isShadow) => Container(
-                  padding: leadingPadding,
-                  width: leadingDimension,
-                  height: leadingDimension,
-                  child: isShadow ? null : leading,
-                )
-            : null,
-        text: title,
-        style: Constants.titleTextStyle,
-        outlineWidth: 2,
-      ),
-    );
-  }
-}

lib/widgets/album/grid/header_generic.dart

@@ -0,0 +1,95 @@
+import 'package:aves/model/collection_lens.dart';
+import 'package:aves/model/image_entry.dart';
+import 'package:aves/utils/constants.dart';
+import 'package:aves/widgets/album/grid/header_album.dart';
+import 'package:aves/widgets/album/grid/header_date.dart';
+import 'package:aves/widgets/common/fx/outlined_text.dart';
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+class SectionHeader extends StatelessWidget {
+  final CollectionLens collection;
+  final Map<dynamic, List<ImageEntry>> sections;
+  final dynamic sectionKey;
+
+  const SectionHeader({
+    Key key,
+    @required this.collection,
+    @required this.sections,
+    @required this.sectionKey,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    Widget header;
+    switch (collection.sortFactor) {
+      case SortFactor.date:
+        if (collection.sortFactor == SortFactor.date) {
+          switch (collection.groupFactor) {
+            case GroupFactor.album:
+              header = _buildAlbumSectionHeader();
+              break;
+            case GroupFactor.month:
+              header = MonthSectionHeader(key: ValueKey(sectionKey), date: sectionKey as DateTime);
+              break;
+            case GroupFactor.day:
+              header = DaySectionHeader(key: ValueKey(sectionKey), date: sectionKey as DateTime);
+              break;
+          }
+        }
+        break;
+      case SortFactor.size:
+        break;
+      case SortFactor.name:
+        header = _buildAlbumSectionHeader();
+        break;
+    }
+    return header != null
+        ? IgnorePointer(
+            child: header,
+          )
+        : const SizedBox.shrink();
+  }
+
+  Widget _buildAlbumSectionHeader() {
+    final folderPath = sectionKey as String;
+    return AlbumSectionHeader(
+      key: ValueKey(folderPath),
+      folderPath: folderPath,
+      albumName: collection.source.getUniqueAlbumName(folderPath),
+    );
+  }
+}
+
+class TitleSectionHeader extends StatelessWidget {
+  final Widget leading;
+  final String title;
+
+  const TitleSectionHeader({Key key, this.leading, this.title}) : super(key: key);
+
+  static const leadingDimension = 32.0;
+  static const leadingPadding = EdgeInsets.only(right: 8, bottom: 4);
+  static const padding = EdgeInsets.all(16);
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      alignment: AlignmentDirectional.centerStart,
+      padding: padding,
+      constraints: const BoxConstraints(minHeight: leadingDimension),
+      child: OutlinedText(
+        leadingBuilder: leading != null
+            ? (context, isShadow) => Container(
+                  padding: leadingPadding,
+                  width: leadingDimension,
+                  height: leadingDimension,
+                  child: isShadow ? null : leading,
+                )
+            : null,
+        text: title,
+        style: Constants.titleTextStyle,
+        outlineWidth: 2,
+      ),
+    );
+  }
+}

lib/widgets/album/search/search_delegate.dart

@@ -1,5 +1,4 @@
 import 'package:aves/model/collection_lens.dart';
-import 'package:aves/model/collection_source.dart';
 import 'package:aves/model/filters/album.dart';
 import 'package:aves/model/filters/favourite.dart';
 import 'package:aves/model/filters/filters.dart';
@@ -68,7 +67,7 @@ class ImageSearchDelegate extends SearchDelegate<CollectionFilter> {
                 _buildFilterRow(
                   context: context,
                   title: 'Albums',
-                  filters: source.sortedAlbums.where(containQuery).map((s) => AlbumFilter(s, CollectionSource.getUniqueAlbumName(s, source.sortedAlbums))).where((f) => containQuery(f.uniqueName)),
+                  filters: source.sortedAlbums.where(containQuery).map((s) => AlbumFilter(s, source.getUniqueAlbumName(s))).where((f) => containQuery(f.uniqueName)),
                 ),
                 _buildFilterRow(
                   context: context,

lib/widgets/album/thumbnail_collection.dart

@@ -5,8 +5,8 @@ import 'package:aves/model/mime_types.dart';
 import 'package:aves/widgets/album/collection_app_bar.dart';
 import 'package:aves/widgets/album/collection_list_sliver.dart';
 import 'package:aves/widgets/album/collection_page.dart';
-import 'package:aves/widgets/album/collection_scaling.dart';
 import 'package:aves/widgets/album/empty.dart';
+import 'package:aves/widgets/album/grid/scaling.dart';
 import 'package:aves/widgets/album/tile_extent_manager.dart';
 import 'package:aves/widgets/common/scroll_thumb.dart';
 import 'package:draggable_scrollbar/draggable_scrollbar.dart';
@@ -71,7 +71,8 @@ class ThumbnailCollection extends StatelessWidget {
                             : CollectionListSliver(
                                 collection: collection,
                                 showHeader: showHeaders,
-                                columnCount: (mqSize.width / tileExtent).round(),
+                                // TODO TLAD get more precise width, considering MediaQuery padding
+                                scrollableWidth: mqSize.width,
                                 tileExtent: tileExtent,
                               ),
                         SliverToBoxAdapter(

lib/widgets/fullscreen/info/basic_section.dart

@@ -1,5 +1,4 @@
 import 'package:aves/model/collection_lens.dart';
-import 'package:aves/model/collection_source.dart';
 import 'package:aves/model/filters/album.dart';
 import 'package:aves/model/filters/favourite.dart';
 import 'package:aves/model/filters/mime.dart';
@@ -53,7 +52,7 @@ class BasicSection extends StatelessWidget {
               if (entry.isVideo) MimeFilter(MimeTypes.ANY_VIDEO),
               if (entry.isGif) MimeFilter(MimeTypes.GIF),
               if (isFavourite) FavouriteFilter(),
-              if (album != null) AlbumFilter(album, CollectionSource.getUniqueAlbumName(album, collection?.source?.sortedAlbums)),
+              if (album != null) AlbumFilter(album, collection?.source?.getUniqueAlbumName(album)),
               ...tags.map((tag) => TagFilter(tag)),
             ]..sort();
             if (filters.isEmpty) return const SizedBox.shrink();