Landing beta changes in master for the new stable release (#747)

platform_design/lib/songs_tab.dart

@@ -15,9 +15,9 @@ class SongsTab extends StatefulWidget {
   static const androidIcon = Icon(Icons.music_note);
   static const iosIcon = Icon(CupertinoIcons.music_note);
 
-  const SongsTab({Key key, this.androidDrawer}) : super(key: key);
+  const SongsTab({Key? key, this.androidDrawer}) : super(key: key);
 
-  final Widget androidDrawer;
+  final Widget? androidDrawer;
 
   @override
   _SongsTabState createState() => _SongsTabState();
@@ -28,8 +28,8 @@ class _SongsTabState extends State<SongsTab> {
 
   final _androidRefreshKey = GlobalKey<RefreshIndicatorState>();
 
-  List<MaterialColor> colors;
-  List<String> songNames;
+  late List<MaterialColor> colors;
+  late List<String> songNames;
 
   @override
   void initState() {
@@ -51,7 +51,7 @@ class _SongsTabState extends State<SongsTab> {
   }
 
   Widget _listBuilder(BuildContext context, int index) {
-    if (index >= _itemsLength) return null;
+    if (index >= _itemsLength) return Container();
 
     // Show a slightly different color palette. Show poppy-ier colors on iOS
     // due to lighter contrasting bars and tone it down on Android.
@@ -96,7 +96,7 @@ class _SongsTabState extends State<SongsTab> {
     // done in a real app but it's done here since this app
     // unrealistically toggles the current platform for demonstration
     // purposes.
-    WidgetsBinding.instance.reassembleApplication();
+    WidgetsBinding.instance!.reassembleApplication();
   }
 
   // ===========================================================================
@@ -117,7 +117,8 @@ class _SongsTabState extends State<SongsTab> {
         actions: [
           IconButton(
             icon: Icon(Icons.refresh),
-            onPressed: () async => await _androidRefreshKey.currentState.show(),
+            onPressed: () async =>
+                await _androidRefreshKey.currentState!.show(),
           ),
           IconButton(
             icon: Icon(Icons.shuffle),
@@ -131,6 +132,7 @@ class _SongsTabState extends State<SongsTab> {
         onRefresh: _refreshData,
         child: ListView.builder(
           padding: EdgeInsets.symmetric(vertical: 12),
+          itemCount: _itemsLength,
           itemBuilder: _listBuilder,
         ),
       ),
@@ -155,7 +157,10 @@ class _SongsTabState extends State<SongsTab> {
           sliver: SliverPadding(
             padding: EdgeInsets.symmetric(vertical: 12),
             sliver: SliverList(
-              delegate: SliverChildBuilderDelegate(_listBuilder),
+              delegate: SliverChildBuilderDelegate(
+                _listBuilder,
+                childCount: _itemsLength,
+              ),
             ),
           ),
         ),