isFirstRun method
Checks if the app is being run for the first time.
Returns a Future<bool?>
that is true
if it's the first run,
false
if it's not, or null
if the value has not been set.
Implementation
Future<bool?> isFirstRun() async {
final sharedPreferences = await SharedPreferences.getInstance();
return sharedPreferences.getBool(firstRunKey);
}