improved widget constructors and main future builder

lib/common/outlined_text.dart

@@ -6,12 +6,13 @@ class OutlinedText extends StatelessWidget {
   final double outlineWidth;
   final Color outlineColor;
 
-  OutlinedText(
+  const OutlinedText(
     this.data, {
+    Key key,
     this.style,
     @required this.outlineWidth,
     @required this.outlineColor,
-  });
+  }) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

lib/image_fullscreen_overlay.dart

@@ -7,7 +7,7 @@ class FullscreenOverlay extends StatefulWidget {
   final List<Map> entries;
   final int index;
 
-  FullscreenOverlay({this.entries, this.index});
+  const FullscreenOverlay({Key key, this.entries, this.index}) : super(key: key);
 
   @override
   State<StatefulWidget> createState() => _FullscreenOverlayState();

lib/image_fullscreen_page.dart

@@ -10,7 +10,11 @@ class ImageFullscreenPage extends StatefulWidget {
   final List<Map> entries;
   final String initialUri;
 
-  ImageFullscreenPage({this.entries, this.initialUri});
+  const ImageFullscreenPage({
+    Key key,
+    this.entries,
+    this.initialUri,
+  }) : super(key: key);
 
   @override
   ImageFullscreenPageState createState() => ImageFullscreenPageState();

lib/main.dart

@@ -16,7 +16,7 @@ class MyApp extends StatelessWidget {
       theme: ThemeData(
         brightness: Brightness.dark,
         accentColor: Colors.amberAccent,
-        scaffoldBackgroundColor: Colors.grey[900]
+        scaffoldBackgroundColor: Colors.grey[900],
       ),
       home: HomePage(),
     );
@@ -29,18 +29,13 @@ class HomePage extends StatefulWidget {
 }
 
 class _HomePageState extends State<HomePage> {
-  List<Map> imageEntryList;
+  Future<List<Map>> _entryListLoader;
 
   @override
   void initState() {
     super.initState();
     imageCache.maximumSizeBytes = 100 * 1024 * 1024;
-    getImageEntries();
-  }
-
-  getImageEntries() async {
-    imageEntryList = await ImageFetcher.getImageEntries();
-    setState(() {});
+    _entryListLoader = ImageFetcher.getImageEntries();
   }
 
   @override
@@ -49,11 +44,17 @@ class _HomePageState extends State<HomePage> {
       // fake app bar so that content is safe from status bar, even though we use a SliverAppBar
       appBar: FakeAppBar(),
       body: Container(
-        child: imageEntryList == null
-            ? Center(
-                child: CircularProgressIndicator(),
-              )
-            : ThumbnailCollection(imageEntryList),
+        child: FutureBuilder(
+          future: _entryListLoader,
+          builder: (futureContext, AsyncSnapshot<List<Map>> snapshot) {
+            if (snapshot.connectionState == ConnectionState.done && !snapshot.hasError) {
+              return ThumbnailCollection(entries: snapshot.data);
+            }
+            return Center(
+              child: CircularProgressIndicator(),
+            );
+          },
+        ),
       ),
       resizeToAvoidBottomInset: false,
     );

lib/model/image_fetcher.dart

@@ -41,7 +41,7 @@ class ImageFetcher {
   }
 
   // return map with: 'aperture' 'exposureTime' 'focalLength' 'iso'
-  static Future<Map> getOverlayMetadata (String path) async {
+  static Future<Map> getOverlayMetadata(String path) async {
     try {
       final result = await platform.invokeMethod('getOverlayMetadata', <String, dynamic>{
         'path': path,

lib/thumbnail.dart

@@ -11,7 +11,7 @@ class Thumbnail extends StatefulWidget {
   final double extent;
   final double devicePixelRatio;
 
-  Thumbnail({
+  const Thumbnail({
     Key key,
     @required this.entry,
     @required this.extent,

lib/thumbnail_collection.dart

@@ -14,13 +14,12 @@ class ThumbnailCollection extends StatelessWidget {
   final Map<DateTime, List<Map>> sections;
   final ScrollController scrollController = ScrollController();
 
-  ThumbnailCollection(this.entries) : sections = groupBy(entries, ImageEntry.getDayTaken);
+  ThumbnailCollection({Key key, this.entries})
+      : sections = groupBy(entries, ImageEntry.getDayTaken),
+        super(key: key);
 
   @override
   Widget build(BuildContext context) {
-    var columnCount = 4;
-    var mediaQuery = MediaQuery.of(context);
-
     return DraggableScrollbar.arrows(
       labelTextBuilder: (double offset) => Text(
         "${offset ~/ 1}",
@@ -34,34 +33,59 @@ class ThumbnailCollection extends StatelessWidget {
             title: Text('Aves - All'),
             floating: true,
           ),
-          ...sections.keys.map((sectionKey) => SliverStickyHeader(
-                header: DaySectionHeader(sectionKey),
-                sliver: SliverGrid(
-                  delegate: SliverChildBuilderDelegate(
-                    (context, index) {
-                      var sectionEntries = sections[sectionKey];
-                      if (index >= sectionEntries.length) return null;
-                      var entry = sectionEntries[index];
-                      return GestureDetector(
-                        onTap: () => _showFullscreen(context, entry),
-                        child: Thumbnail(
-                          entry: entry,
-                          extent: mediaQuery.size.width / columnCount,
-                          devicePixelRatio: mediaQuery.devicePixelRatio,
-                        ),
-                      );
-                    },
-                    childCount: sections[sectionKey].length,
-                  ),
-                  gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
-                    crossAxisCount: columnCount,
-                  ),
-                ),
-              ))
+          ...sections.keys.map((sectionKey) => SectionSliver(
+                entries: entries,
+                sections: sections,
+                sectionKey: sectionKey,
+              )),
         ],
       ),
     );
   }
+}
+
+class SectionSliver extends StatelessWidget {
+  final List<Map> entries;
+  final Map<DateTime, List<Map>> sections;
+  final DateTime sectionKey;
+
+  const SectionSliver({
+    Key key,
+    this.entries,
+    this.sections,
+    this.sectionKey,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    var columnCount = 4;
+    var mediaQuery = MediaQuery.of(context);
+
+    return SliverStickyHeader(
+      header: DaySectionHeader(date: sectionKey),
+      sliver: SliverGrid(
+        delegate: SliverChildBuilderDelegate(
+          (context, index) {
+            var sectionEntries = sections[sectionKey];
+            if (index >= sectionEntries.length) return null;
+            var entry = sectionEntries[index];
+            return GestureDetector(
+              onTap: () => _showFullscreen(context, entry),
+              child: Thumbnail(
+                entry: entry,
+                extent: mediaQuery.size.width / columnCount,
+                devicePixelRatio: mediaQuery.devicePixelRatio,
+              ),
+            );
+          },
+          childCount: sections[sectionKey].length,
+        ),
+        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
+          crossAxisCount: columnCount,
+        ),
+      ),
+    );
+  }
 
   Future _showFullscreen(BuildContext context, Map entry) {
     return Navigator.push(
@@ -79,6 +103,10 @@ class ThumbnailCollection extends StatelessWidget {
 class DaySectionHeader extends StatelessWidget {
   final String text;
 
+  DaySectionHeader({Key key, DateTime date})
+      : text = formatDate(date),
+        super(key: key);
+
   static DateFormat md = DateFormat.MMMMd();
   static DateFormat ymd = DateFormat.yMMMMd();
 
@@ -88,25 +116,23 @@ class DaySectionHeader extends StatelessWidget {
     return ymd.format(date);
   }
 
-  DaySectionHeader(DateTime date) : text = formatDate(date);
-
   @override
   Widget build(BuildContext context) {
-    return SectionHeader(text);
+    return SectionHeader(text: text);
   }
 }
 
 class SectionHeader extends StatelessWidget {
-  final String primaryText;
+  final String text;
 
-  SectionHeader(this.primaryText);
+  const SectionHeader({Key key, this.text}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
     return Container(
       padding: EdgeInsets.all(16),
       child: OutlinedText(
-        primaryText,
+        text,
         style: TextStyle(
           color: Colors.grey[200],
           fontSize: 20,