veggieseasons: Migrate to null safety (#922)

veggieseasons/lib/widgets/close_button.dart

@@ -12,10 +12,10 @@ import 'package:veggieseasons/styles.dart';
 class FrostedBox extends StatelessWidget {
   const FrostedBox({
     this.child,
-    Key key,
+    Key? key,
   }) : super(key: key);
 
-  final Widget child;
+  final Widget? child;
 
   @override
   Widget build(BuildContext context) {
@@ -37,18 +37,15 @@ class ColorChangingIcon extends ImplicitlyAnimatedWidget {
     this.icon, {
     this.color = CupertinoColors.black,
     this.size,
-    @required Duration duration,
-    Key key,
-  })  : assert(icon != null),
-        assert(color != null),
-        assert(duration != null),
-        super(key: key, duration: duration);
+    required Duration duration,
+    Key? key,
+  }) : super(key: key, duration: duration);
 
   final Color color;
 
   final IconData icon;
 
-  final double size;
+  final double? size;
 
   @override
   _ColorChangingIconState createState() => _ColorChangingIconState();
@@ -56,7 +53,7 @@ class ColorChangingIcon extends ImplicitlyAnimatedWidget {
 
 class _ColorChangingIconState
     extends AnimatedWidgetBaseState<ColorChangingIcon> {
-  ColorTween _colorTween;
+  ColorTween? _colorTween;
 
   @override
   Widget build(BuildContext context) {
@@ -73,14 +70,14 @@ class _ColorChangingIconState
     _colorTween = visitor(
       _colorTween,
       widget.color,
-      (dynamic value) => ColorTween(begin: value as Color),
-    ) as ColorTween;
+      (dynamic value) => ColorTween(begin: value as Color?),
+    ) as ColorTween?;
   }
 }
 
 /// A simple "close this modal" button that invokes a callback when pressed.
 class CloseButton extends StatefulWidget {
-  const CloseButton(this.onPressed, {Key key}) : super(key: key);
+  const CloseButton(this.onPressed, {Key? key}) : super(key: key);
 
   final VoidCallback onPressed;
 

veggieseasons/lib/widgets/settings_group.dart

@@ -14,7 +14,7 @@ import 'settings_item.dart';
 // See https://github.com/flutter/flutter/projects/29 for more info.
 
 class SettingsGroupHeader extends StatelessWidget {
-  const SettingsGroupHeader(this.title, {Key key}) : super(key: key);
+  const SettingsGroupHeader(this.title, {Key? key}) : super(key: key);
 
   final String title;
 
@@ -35,7 +35,7 @@ class SettingsGroupHeader extends StatelessWidget {
 }
 
 class SettingsGroupFooter extends StatelessWidget {
-  const SettingsGroupFooter(this.title, {Key key}) : super(key: key);
+  const SettingsGroupFooter(this.title, {Key? key}) : super(key: key);
 
   final String title;
 
@@ -55,17 +55,16 @@ class SettingsGroupFooter extends StatelessWidget {
 
 class SettingsGroup extends StatelessWidget {
   SettingsGroup({
-    @required this.items,
+    required this.items,
     this.header,
     this.footer,
-    Key key,
-  })  : assert(items != null),
-        assert(items.isNotEmpty),
+    Key? key,
+  })  : assert(items.isNotEmpty),
         super(key: key);
 
   final List<SettingsItem> items;
-  final Widget header;
-  final Widget footer;
+  final Widget? header;
+  final Widget? footer;
   @override
   Widget build(BuildContext context) {
     var brightness = CupertinoTheme.brightnessOf(context);
@@ -85,7 +84,7 @@ class SettingsGroup extends StatelessWidget {
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          if (header != null) header,
+          if (header != null) header!,
           Container(
             decoration: BoxDecoration(
               color: CupertinoColors.white,
@@ -105,7 +104,7 @@ class SettingsGroup extends StatelessWidget {
               children: dividedItems,
             ),
           ),
-          if (footer != null) footer,
+          if (footer != null) footer!,
         ],
       ),
     );

veggieseasons/lib/widgets/settings_item.dart

@@ -16,7 +16,7 @@ import 'package:veggieseasons/styles.dart';
 typedef SettingsItemCallback = FutureOr<void> Function();
 
 class SettingsNavigationIndicator extends StatelessWidget {
-  const SettingsNavigationIndicator({Key key}) : super(key: key);
+  const SettingsNavigationIndicator({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -30,12 +30,11 @@ class SettingsNavigationIndicator extends StatelessWidget {
 
 class SettingsIcon extends StatelessWidget {
   const SettingsIcon({
-    @required this.icon,
+    required this.icon,
     this.foregroundColor = CupertinoColors.white,
     this.backgroundColor = CupertinoColors.black,
-    Key key,
-  })  : assert(icon != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
   final Color backgroundColor;
   final Color foregroundColor;
@@ -61,20 +60,19 @@ class SettingsIcon extends StatelessWidget {
 
 class SettingsItem extends StatefulWidget {
   const SettingsItem({
-    @required this.label,
+    required this.label,
     this.icon,
     this.content,
     this.subtitle,
     this.onPress,
-    Key key,
-  })  : assert(label != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
   final String label;
-  final Widget icon;
-  final Widget content;
-  final String subtitle;
-  final SettingsItemCallback onPress;
+  final Widget? icon;
+  final Widget? content;
+  final String? subtitle;
+  final SettingsItemCallback? onPress;
 
   @override
   State<StatefulWidget> createState() => SettingsItemState();
@@ -97,7 +95,7 @@ class SettingsItemState extends State<SettingsItem> {
             setState(() {
               pressed = true;
             });
-            await widget.onPress();
+            await widget.onPress!();
             Future.delayed(
               const Duration(milliseconds: 150),
               () {
@@ -138,7 +136,7 @@ class SettingsItemState extends State<SettingsItem> {
                                 style: themeData.textTheme.textStyle),
                             const SizedBox(height: 4),
                             Text(
-                              widget.subtitle,
+                              widget.subtitle!,
                               style: Styles.settingsItemSubtitleText(themeData),
                             ),
                           ],

veggieseasons/lib/widgets/trivia.dart

@@ -8,10 +8,10 @@ import 'package:veggieseasons/styles.dart';
 /// Presents a series of trivia questions about a particular widget, and tracks
 /// the user's score.
 class TriviaView extends StatefulWidget {
-  final int id;
-  final String restorationId;
+  final int? id;
+  final String? restorationId;
 
-  const TriviaView({this.id, this.restorationId, Key key}) : super(key: key);
+  const TriviaView({this.id, this.restorationId, Key? key}) : super(key: key);
 
   @override
   _TriviaViewState createState() => _TriviaViewState();
@@ -26,10 +26,10 @@ enum PlayerStatus {
 
 class _TriviaViewState extends State<TriviaView> with RestorationMixin {
   /// Current app state. This is used to fetch veggie data.
-  AppState appState;
+  late AppState appState;
 
   /// The veggie trivia about which to show.
-  Veggie veggie;
+  late Veggie veggie;
 
   /// Index of the current trivia question.
   RestorableInt triviaIndex = RestorableInt(0);
@@ -45,10 +45,10 @@ class _TriviaViewState extends State<TriviaView> with RestorationMixin {
       _RestorablePlayerStatus(PlayerStatus.readyToAnswer);
 
   @override
-  String get restorationId => widget.restorationId;
+  String? get restorationId => widget.restorationId;
 
   @override
-  void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
     registerForRestoration(triviaIndex, 'index');
     registerForRestoration(score, 'score');
     registerForRestoration(status, 'status');
@@ -234,7 +234,7 @@ class _RestorablePlayerStatus extends RestorableValue<PlayerStatus> {
   }
 
   @override
-  PlayerStatus fromPrimitives(Object data) {
+  PlayerStatus fromPrimitives(Object? data) {
     return PlayerStatus.values[data as int];
   }
 
@@ -244,7 +244,7 @@ class _RestorablePlayerStatus extends RestorableValue<PlayerStatus> {
   }
 
   @override
-  void didUpdateValue(PlayerStatus oldValue) {
+  void didUpdateValue(PlayerStatus? oldValue) {
     notifyListeners();
   }
 }

veggieseasons/lib/widgets/veggie_card.dart

@@ -14,12 +14,12 @@ class FrostyBackground extends StatelessWidget {
     this.color,
     this.intensity = 25,
     this.child,
-    Key key,
+    Key? key,
   }) : super(key: key);
 
-  final Color color;
+  final Color? color;
   final double intensity;
-  final Widget child;
+  final Widget? child;
 
   @override
   Widget build(BuildContext context) {
@@ -41,23 +41,17 @@ class FrostyBackground extends StatelessWidget {
 /// elevation and invoking an optional [onPressed] callback.
 class PressableCard extends StatefulWidget {
   const PressableCard({
-    @required this.child,
+    required this.child,
     this.borderRadius = const BorderRadius.all(Radius.circular(5)),
     this.upElevation = 2,
     this.downElevation = 0,
     this.shadowColor = CupertinoColors.black,
     this.duration = const Duration(milliseconds: 100),
     this.onPressed,
-    Key key,
-  })  : assert(child != null),
-        assert(borderRadius != null),
-        assert(upElevation != null),
-        assert(downElevation != null),
-        assert(shadowColor != null),
-        assert(duration != null),
-        super(key: key);
+    Key? key,
+  }) : super(key: key);
 
-  final VoidCallback onPressed;
+  final VoidCallback? onPressed;
 
   final Widget child;
 
@@ -84,7 +78,7 @@ class _PressableCardState extends State<PressableCard> {
       onTap: () {
         setState(() => cardIsDown = false);
         if (widget.onPressed != null) {
-          widget.onPressed();
+          widget.onPressed!();
         }
       },
       onTapDown: (details) => setState(() => cardIsDown = true),
@@ -107,7 +101,7 @@ class _PressableCardState extends State<PressableCard> {
 
 class VeggieCard extends StatelessWidget {
   const VeggieCard(this.veggie, this.isInSeason, this.isPreferredCategory,
-      {Key key})
+      {Key? key})
       : super(key: key);
 
   /// Veggie to be displayed by the card.

veggieseasons/lib/widgets/veggie_headline.dart

@@ -8,17 +8,17 @@ import 'package:veggieseasons/screens/details.dart';
 import 'package:veggieseasons/styles.dart';
 
 class ZoomClipAssetImage extends StatelessWidget {
-  const ZoomClipAssetImage(
-      {@required this.zoom,
-      this.height,
-      this.width,
-      @required this.imageAsset,
-      Key key})
-      : super(key: key);
+  const ZoomClipAssetImage({
+    required this.zoom,
+    this.height,
+    this.width,
+    required this.imageAsset,
+    Key? key,
+  }) : super(key: key);
 
   final double zoom;
-  final double height;
-  final double width;
+  final double? height;
+  final double? width;
   final String imageAsset;
 
   @override
@@ -30,8 +30,8 @@ class ZoomClipAssetImage extends StatelessWidget {
       child: ClipRRect(
         borderRadius: BorderRadius.circular(10),
         child: OverflowBox(
-          maxHeight: height * zoom,
-          maxWidth: width * zoom,
+          maxHeight: height! * zoom,
+          maxWidth: width! * zoom,
           child: Image.asset(
             imageAsset,
             fit: BoxFit.fill,
@@ -45,7 +45,7 @@ class ZoomClipAssetImage extends StatelessWidget {
 class VeggieHeadline extends StatelessWidget {
   final Veggie veggie;
 
-  const VeggieHeadline(this.veggie, {Key key}) : super(key: key);
+  const VeggieHeadline(this.veggie, {Key? key}) : super(key: key);
 
   List<Widget> _buildSeasonDots(List<Season> seasons) {
     var widgets = <Widget>[];