use final where possible

lib/common/draggable_scrollbar.dart

@@ -128,7 +128,7 @@ class DraggableScrollbar extends StatefulWidget {
   _DraggableScrollbarState createState() => _DraggableScrollbarState();
 
   static buildScrollThumbAndLabel({@required Widget scrollThumb, @required Color backgroundColor, @required Animation<double> thumbAnimation, @required Animation<double> labelAnimation, @required Text labelText, @required BoxConstraints labelConstraints, @required bool alwaysVisibleScrollThumb}) {
-    var scrollThumbAndLabel = labelText == null
+    final scrollThumbAndLabel = labelText == null
         ? scrollThumb
         : Row(
             mainAxisSize: MainAxisSize.min,

lib/image_fullscreen_overlay.dart

@@ -39,9 +39,9 @@ class _FullscreenOverlayState extends State<FullscreenOverlay> {
 
   @override
   Widget build(BuildContext context) {
-    var viewInsets = MediaQuery.of(context).viewInsets;
+    final viewInsets = MediaQuery.of(context).viewInsets;
-    var date = ImageEntry.getBestDate(entry);
+    final date = ImageEntry.getBestDate(entry);
-    var subRowConstraints = BoxConstraints(maxWidth: 400);
+    final subRowConstraints = BoxConstraints(maxWidth: 400);
     return IgnorePointer(
       child: Container(
         padding: EdgeInsets.all(8.0).add(EdgeInsets.only(bottom: viewInsets.bottom)),

lib/image_fullscreen_page.dart

@@ -29,7 +29,7 @@ class ImageFullscreenPageState extends State<ImageFullscreenPage> {
   @override
   void initState() {
     super.initState();
-    var index = entries.indexWhere((entry) => entry['uri'] == widget.initialUri);
+    final index = entries.indexWhere((entry) => entry['uri'] == widget.initialUri);
     _currentPage = max(0, index);
     _pageController = PageController(initialPage: _currentPage);
   }
@@ -49,7 +49,7 @@ class ImageFullscreenPageState extends State<ImageFullscreenPage> {
           PhotoViewGallery.builder(
             itemCount: entries.length,
             builder: (context, index) {
-              var entry = entries[index];
+              final entry = entries[index];
               return PhotoViewGalleryPageOptions(
                 imageProvider: FileImage(File(entry['path'])),
                 heroTag: entry['uri'],

lib/model/image_entry.dart

@@ -1,16 +1,16 @@
 class ImageEntry {
   static DateTime getBestDate(Map entry) {
-    var dateTakenMillis = entry['sourceDateTakenMillis'] as int;
+    final dateTakenMillis = entry['sourceDateTakenMillis'] as int;
     if (dateTakenMillis != null && dateTakenMillis > 0) return DateTime.fromMillisecondsSinceEpoch(dateTakenMillis);
 
-    var dateModifiedSecs = entry['dateModifiedSecs'] as int;
+    final dateModifiedSecs = entry['dateModifiedSecs'] as int;
     if (dateModifiedSecs != null && dateModifiedSecs > 0) return DateTime.fromMillisecondsSinceEpoch(dateModifiedSecs * 1000);
 
     return null;
   }
 
   static DateTime getDayTaken(Map entry) {
-    var d = getBestDate(entry);
+    final d = getBestDate(entry);
     return d == null ? null : DateTime(d.year, d.month, d.day);
   }
 }

lib/thumbnail.dart

@@ -45,7 +45,7 @@ class ThumbnailState extends State<Thumbnail> {
   }
 
   initByteLoader() {
-    var dim = (widget.extent * widget.devicePixelRatio).round();
+    final dim = (widget.extent * widget.devicePixelRatio).round();
     _byteLoader = ImageFetcher.getImageBytes(widget.entry, dim, dim);
   }
 
@@ -58,9 +58,9 @@ class ThumbnailState extends State<Thumbnail> {
 
   @override
   Widget build(BuildContext context) {
-    var isVideo = mimeType.startsWith(MimeTypes.MIME_VIDEO);
+    final isVideo = mimeType.startsWith(MimeTypes.MIME_VIDEO);
-    var isGif = mimeType == MimeTypes.MIME_GIF;
+    final isGif = mimeType == MimeTypes.MIME_GIF;
-    var iconSize = widget.extent / 4;
+    final iconSize = widget.extent / 4;
     return Container(
       decoration: BoxDecoration(
         border: Border.all(
@@ -71,7 +71,7 @@ class ThumbnailState extends State<Thumbnail> {
       child: FutureBuilder(
           future: _byteLoader,
           builder: (futureContext, AsyncSnapshot<Uint8List> snapshot) {
-            var bytes = (snapshot.connectionState == ConnectionState.done && !snapshot.hasError) ? snapshot.data : kTransparentImage;
+            final bytes = (snapshot.connectionState == ConnectionState.done && !snapshot.hasError) ? snapshot.data : kTransparentImage;
             return Stack(
               alignment: AlignmentDirectional.bottomStart,
               children: [
@@ -81,7 +81,7 @@ class ThumbnailState extends State<Thumbnail> {
                     // during hero animation back from a fullscreen image,
                     // the image covers the whole screen (because of the 'fit' prop and the full screen hero constraints)
                     // so we wrap the image to apply better constraints
-                    var dim = min(constraints.maxWidth, constraints.maxHeight);
+                    final dim = min(constraints.maxWidth, constraints.maxHeight);
                     return Container(
                       alignment: Alignment.center,
                       constraints: BoxConstraints.tight(Size(dim, dim)),

lib/thumbnail_collection.dart

@@ -60,19 +60,18 @@ class SectionSliver extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
 //    debugPrint('$runtimeType build with sectionKey=$sectionKey');
-    var columnCount = 4;
+    final columnCount = 4;
-    var mediaQuery = MediaQuery.of(context);
-
     return SliverStickyHeader(
       header: DaySectionHeader(date: sectionKey),
       sliver: SliverGrid(
         delegate: SliverChildBuilderDelegate(
-          (context, index) {
+          (sliverContext, index) {
-            var sectionEntries = sections[sectionKey];
+            final sectionEntries = sections[sectionKey];
             if (index >= sectionEntries.length) return null;
-            var entry = sectionEntries[index];
+            final entry = sectionEntries[index];
+            final mediaQuery = MediaQuery.of(sliverContext);
             return GestureDetector(
-              onTap: () => _showFullscreen(context, entry),
+              onTap: () => _showFullscreen(sliverContext, entry),
               child: Thumbnail(
                 entry: entry,
                 extent: mediaQuery.size.width / columnCount,