Flutter Theming

Goal

Updates and manages Flutter application styling by migrating legacy Material 2 implementations to Material 3, normalizing component themes, updating deprecated button classes, and adapting UI idioms for cross-platform consistency. Assumes a Flutter environment using Dart.

Instructions

1. Analyze Current Theme State Review the existing Flutter codebase to identify legacy Material 2 components, deprecated button classes (FlatButton, RaisedButton, OutlineButton), and outdated theme properties (e.g., accentColor, color in AppBarTheme). STOP AND ASK THE USER: "What is the primary seed color for the new Material 3 ColorScheme, and which target platforms (iOS, Android, Windows, macOS, Linux, Web) should be prioritized for platform idioms?"

2. Decision Logic: Component Migration When encountering legacy widgets, use the following decision tree to determine the replacement:

   • IF BottomNavigationBar -> REPLACE WITH NavigationBar (uses NavigationDestination).
   • IF Drawer -> REPLACE WITH NavigationDrawer (uses NavigationDrawerDestination).
   • IF ToggleButtons -> REPLACE WITH SegmentedButton (uses ButtonSegment and Set for selection).
   • IF FlatButton -> REPLACE WITH TextButton.
   • IF RaisedButton -> REPLACE WITH ElevatedButton (or FilledButton for no elevation).
   • IF OutlineButton -> REPLACE WITH OutlinedButton.

3. Implement App-Wide Material 3 Theme Define the global ThemeData using ColorScheme.fromSeed. Ensure useMaterial3 is implicitly or explicitly true. Remove all references to deprecated accent properties (accentColor, accentColorBrightness, accentTextTheme, accentIconTheme).

   MaterialApp(
     title: 'App Name',
     theme: ThemeData(
       useMaterial3: true,
       colorScheme: ColorScheme.fromSeed(
         seedColor: Colors.deepPurple,
         brightness: Brightness.light,
       ),
       // Use colorScheme.secondary instead of accentColor
     ),
     darkTheme: ThemeData(
       useMaterial3: true,
       colorScheme: ColorScheme.fromSeed(
         seedColor: Colors.deepPurple,
         brightness: Brightness.dark,
       ),
     ),
     home: const MyHomePage(),
   );
   

4. Normalize Component Themes Update all component theme definitions in ThemeData to use their *ThemeData equivalents. Do not use the base theme classes for configuration.

   • cardTheme -> CardThemeData
   • dialogTheme -> DialogThemeData
   • tabBarTheme -> TabBarThemeData
   • appBarTheme -> AppBarThemeData (Replace color with backgroundColor)
   • bottomAppBarTheme -> BottomAppBarThemeData
   • inputDecorationTheme -> InputDecorationThemeData

   ThemeData(
     colorScheme: ColorScheme.fromSeed(seedColor: Colors.blue),
     appBarTheme: const AppBarThemeData(
       backgroundColor: Colors.blue, // Do not use 'color'
       elevation: 4.0,
     ),
     cardTheme: const CardThemeData(
       elevation: 2.0,
     ),
   );
   

5. Migrate Buttons and Button Styles Replace legacy buttons. Use the styleFrom() static method for simple overrides, or ButtonStyle with MaterialStateProperty for state-dependent styling.

   // Simple override using styleFrom
   TextButton(
     style: TextButton.styleFrom(
       foregroundColor: Colors.blue,
       disabledForegroundColor: Colors.red,
     ),
     onPressed: () {},
     child: const Text('TextButton'),
   )
   
   // State-dependent override using MaterialStateProperty
   OutlinedButton(
     style: ButtonStyle(
       side: MaterialStateProperty.resolveWith<BorderSide>(
         (Set<MaterialState> states) {
           if (states.contains(MaterialState.pressed)) {
             return const BorderSide(color: Colors.blue, width: 2);
           }
           return const BorderSide(color: Colors.grey, width: 1);
         }
       ),
     ),
     onPressed: () {},
     child: const Text('OutlinedButton'),
   )
   

6. Decision Logic: Platform Idioms Apply platform-specific adaptations based on the host OS to reduce cognitive load and build user trust.

   • Scrollbars: IF desktop platform -> Set thumbVisibility: true (or alwaysShown). IF mobile -> Use default auto-hiding behavior.
   • Text Selection: IF text is informational and non-interactive -> Wrap in SelectableText to allow mouse selection on Web/Desktop.
   • Button Ordering: IF Windows -> Place confirmation button on the LEFT. IF macOS/Linux/Android/iOS -> Place confirmation button on the RIGHT.

   // Platform-aware button ordering
   TextDirection btnDirection = Platform.isWindows 
       ? TextDirection.rtl 
       : TextDirection.ltr;
   
   Row(
     children: [
       const Spacer(),
       Row(
         textDirection: btnDirection,
         children: [
           TextButton(
             onPressed: () => Navigator.pop(context, false),
             child: const Text('Cancel'),
           ),
           ElevatedButton(
             onPressed: () => Navigator.pop(context, true),
             child: const Text('OK'),
           ),
         ],
       ),
     ],
   )
   

7. Validate-and-Fix Scan the generated code to verify that no FlatButton, RaisedButton, OutlineButton, or ButtonTheme classes remain. Verify that AppBarTheme does not use the color property. Fix any instances found.

Constraints

• Single Source of Truth: All colors must be derived from the ColorScheme (e.g., Theme.of(context).colorScheme.primary). Do not hardcode hex colors unless explicitly requested.
• No Legacy Buttons: Never output FlatButton, RaisedButton, or OutlineButton.
• No Accent Properties: Never use accentColor, accentColorBrightness, accentTextTheme, or accentIconTheme. Use colorScheme.secondary and colorScheme.onSecondary instead.
• Component Theme Suffixes: Always append Data to component themes when configuring ThemeData (e.g., CardThemeData, not CardTheme).
• AppBar Background: Never use the color property in AppBarTheme or AppBarThemeData; strictly use backgroundColor.