Flutter: How to get a value inside ThemeData?

Question

I'm trying to style my app globally and I have some questions about hot the properly retrieve the value like this!

This code it's not working because there is no context at this point, but is there some way to get this value?

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';

ThemeData lightTheme = ThemeData(
  useMaterial3: true,
  
  // Text Style
  textTheme: TextTheme(
    titleMedium: GoogleFonts.nunito(fontWeight: FontWeight.bold, letterSpacing: -1, fontSize: 16),
  ),

  // AppBar
  appBarTheme: AppBarTheme(
    titleTextStyle: Theme.of(context).textTheme.titleMedium,
  ),
);

Answer 1

Instead of globally declaring theme data, use a class with static method returning themeData with context as parameter:

@override
Widget build(BuildContext context) {
  return MaterialApp(
    theme: ThemeClass.getThemeData(context),
    home: const HomePage(),
  );
}

class ThemeClass {
  static ThemeData getThemeData(BuildContext context) {
    final lightTheme = ThemeData(
      useMaterial3: true,

      // Text Style
      textTheme: TextTheme(
        titleMedium: GoogleFonts.nunito(
            fontWeight: FontWeight.bold, letterSpacing: -1, fontSize: 16),
      ),

      // AppBar
      appBarTheme: AppBarTheme(
        titleTextStyle: Theme.of(context).textTheme.titleMedium,
      ),
    );

    return lightTheme;
  }

Answer 2

Create dark & light mode extension

extension Context on BuildContext {
     bool get isDarkMode => Theme.of(this).brightness == Brightness.dark;
}

Create your them file

class ConstTheme {
  /// Light theme color
  static ThemeData light = ThemeData(
    useMaterial3: true,
    fontFamily: 'DM Sans',
    colorSchemeSeed: ConstColor.primary,
    brightness: Brightness.light,
    scaffoldBackgroundColor: ConstColor.white,
    textTheme: const TextTheme(
      titleSmall: TextStyle(color: ConstColor.black),
      titleMedium: TextStyle(color: ConstColor.black),
    ),
    cardTheme: CardTheme(
      margin: EdgeInsets.zero,
      elevation: 2.0,
      color: ConstColor.white,
      clipBehavior: Clip.hardEdge,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(10),
      ),
    ),
  );

  /// Dark theme color
  static ThemeData dark = ThemeData(
    useMaterial3: true,
    fontFamily: 'DM Sans',
    colorSchemeSeed: ConstColor.primary,
    brightness: Brightness.dark,
    scaffoldBackgroundColor: const Color(0xff151616),
    cardTheme: CardTheme(
      margin: EdgeInsets.zero,
      elevation: 2.0,
      color: const Color(0xff1C1E1F),
      // surfaceTintColor: const Color(0xff1C1E1F),
      clipBehavior: Clip.hardEdge,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(10),
      ),
      // shadowColor: Colors.white.withOpacity(0.5),
    ),
  );