setTheme method
Change the theme of the app (dark/light) depending on a boolean toggle value. Notify listeners (main Material App) when called, to rebuild the entire widget tree.
themeMode: ThemeMode value, usually provided by a toggle. If equals ThemeMode.light, set light theme,
otherwise set dark theme.
Implementation
Future setTheme(ThemeMode themeMode) async {
this.themeMode = themeMode;
await _saveThemePreference(mode: themeMode);
SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
statusBarBrightness:
themeMode == ThemeMode.light ? Brightness.light : Brightness.dark));
notifyListeners();
}