Here, What I needed is :

"Changing Overall Application Font's Size" according to selected values from Application's Setting as below :

Here, I am not talking about the support of font size in different screen sizes of device. This is different thing, means font size should change according to selected values as 'small' , 'medium', 'large'.

Is there any better way to achieve this? Thanks.

CodePudding user response：

Use ChangeNotifierProvider and ChangeNotifier. This will allow to rebuild your entire app if you wrap your root widget i.e. MyApp which contains your MaterialApp within the ChangeNotifierProvider. Below is a sample piece of code:

// Changable Settings class
class AppSettings extends ChangeNotifier
{
   double fontSize;
   // TextStyle textStyle;
   
    void update() {     
        notifyListeners();
    }
}

// ChangeNotifier setup in main
main()
{
    runApp(
      MultiProvider(
        providers: [
          ChangeNotifierProvider(create: (_) => AppSettings()),
        ],
        child: MyApp(),
      ),
    );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
   Consumer<AppSettings >(builder: (context, appSettings, child) {
      return MaterialApp(
        theme: ThemeData().copyWith(   // Apply the theme to whole app
          textTheme: TextTheme(
            titleSmall: Theme.of(context)
                .textTheme
                .titleSmall
                .copyWith(fontSize: appSettings.fontSize), // Font Size apply
          ),
        ),
        home: homePage,
      );
    });
  }
}

// Get the change from user from the settings page
class SettingsPage extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
   ...
  }
  
  onSave(){
    var appSettings = Provider.of<AppSettings>(context);
    appSettings.fontSize = fontSize; // from the UI
    appSettings.update();
  }
}

Hope it gives some start point to you.