how to check if SharedPreferences exists for this application in flutter

Question

my flutter application checks for saved data in SharedPreferences every time it starts . to use it later in the application, but when I run the app for the first time in a device, there is saved SharedPreferences yet so it gets all the data as null. so I want to make sure that it checks if the file itself exists rather than checking for a specific value,

note: I'm using this shared_preferences futter package.

here is my code :

  checkingTheSavedData() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    String username = prefs.getString('username');
    if (username == null) {
      Navigator.pushReplacementNamed(context, '/login');
    } else {
      Navigator.pushReplacementNamed(context, '/main_page');
    }
  }

So, for the frist run it does Navigator.pushReplacementNamed(context, '/main_page'); but with empty data , after that when i do a real login and the data is already saved , it works fine. any idea how to handle this in a proper way ?

Answer 1

You need to check if the key exists yet by using prefs.containsKey('username').

Answer 2

When I use "shared_preferences", I personally use an helper to get and set just like this :

GETTER

static Future<String> getUserName() async { 
  final SharedPreferences prefs = await SharedPreferences.getInstance();
  return prefs.getString('username') ?? '';
}

SETTER

static Future<String> setUserName(String value) async {
  final SharedPreferences prefs = await SharedPreferences.getInstance();
  return prefs.setString('username', value);
}

To answer your question, you can't check if the SharedPreferences "file" exist or not. Your method is already correct.