selection: toggle section selection by tapping header

lib/widgets/album/grid/header_generic.dart

@@ -129,6 +129,8 @@ class TitleSectionHeader extends StatelessWidget {
       alignment: AlignmentDirectional.centerStart,
       padding: padding,
       constraints: const BoxConstraints(minHeight: leadingDimension),
+      child: GestureDetector(
+        onTap: () => _toggleSectionSelection(context),
         child: Text.rich(
           TextSpan(
             children: [
@@ -144,6 +146,7 @@ class TitleSectionHeader extends StatelessWidget {
                             child: leading,
                           )
                       : null,
+                  onPressed: () => _toggleSectionSelection(context),
                 ),
               ),
               TextSpan(
@@ -161,18 +164,32 @@ class TitleSectionHeader extends StatelessWidget {
             ],
           ),
         ),
+      ),
     );
   }
+
+  void _toggleSectionSelection(BuildContext context) {
+    final collection = Provider.of<CollectionLens>(context, listen: false);
+    final sectionEntries = collection.sections[sectionKey];
+    final selected = collection.isSelected(sectionEntries);
+    if (selected) {
+      collection.removeFromSelection(sectionEntries);
+    } else {
+      collection.addToSelection(sectionEntries);
+    }
+  }
 }
 
 class SectionSelectableLeading extends StatelessWidget {
   final dynamic sectionKey;
   final WidgetBuilder browsingBuilder;
+  final VoidCallback onPressed;
 
   const SectionSelectableLeading({
     Key key,
     @required this.sectionKey,
     @required this.browsingBuilder,
+    @required this.onPressed,
   }) : super(key: key);
 
   static const leadingDimension = TitleSectionHeader.leadingDimension;
@@ -199,13 +216,7 @@ class SectionSelectableLeading extends StatelessWidget {
                       padding: const EdgeInsets.only(top: 1),
                       alignment: Alignment.topLeft,
                       icon: Icon(selected ? AIcons.selected : AIcons.unselected),
-                      onPressed: () {
+                      onPressed: onPressed,
-                        if (selected) {
-                          collection.removeFromSelection(sectionEntries);
-                        } else {
-                          collection.addToSelection(sectionEntries);
-                        }
-                      },
                       tooltip: selected ? 'Deselect section' : 'Select section',
                       constraints: const BoxConstraints(
                         minHeight: leadingDimension,