Flutter Custom TextTheme With Adaptive TextSize

Question

I created custom ThemeDatas (light & dark), when I launch my app with them I get a _mulFromInteger() issue. This is because the FontSizes in TextTheme inside my ThemeData have values that change according to the screen size, to make these adaptive FontSizes I use a class that contains my size configurations. This class calls MediaQuery.of(context) that will modify my screen configurations in function to it's value. The problem is that I call my ThemeData (with the TextTheme) before I call my SizeConfigurations.init(context). If I try putting my init before creating my MaterialApp and setting the theme it tells me I used a context without a MediaQuery. Any idea how to solve this? Thanks:)

Code:

  @override
  Widget build(BuildContext context) {
    // When I call SizeConfig().init(context); here it tells me the context doesn't have a MediaQuery
    return MaterialApp(
      theme: AppTheme.getLightTheme(),
      darkTheme: AppTheme.getDarkTheme(),
      themeMode: ThemeMode.system,
      title: 'App Title',
      onGenerateRoute: NavigationRouter.generateRoute,
      home: FutureBuilder(
        future: jwtOrEmpty,            
        builder: (context, snapshot) {
          SizeConfig().init(context);
          …
        }
      ),
    );
  }

Answer 1

You can copy paste run full code below
You can use MediaQueryData.fromWindow(ui.window)
code snippet

void init() {
    _mediaQueryData = MediaQueryData.fromWindow(ui.window);
    _screenWidth = _mediaQueryData.size.width;
    _screenHeight = _mediaQueryData.size.height;

full code

import 'package:flutter/material.dart';
import 'dart:ui' as ui;

class SizeConfig {
  static MediaQueryData _mediaQueryData;
  static double _screenWidth;
  static double _screenHeight;

  double get screenWidth => _screenWidth;
  double get screenHeight => _screenHeight;

 void init() {
    _mediaQueryData = MediaQueryData.fromWindow(ui.window);
    _screenWidth = _mediaQueryData.size.width;
    _screenHeight = _mediaQueryData.size.height;
    print(_screenWidth);
    print(_screenHeight);
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    SizeConfig().init();

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    print(MediaQuery.of(context).size.width);
    print(MediaQuery.of(context).size.height);
    print(SizeConfig().screenWidth);

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}