颤动的共享偏好问题

Question

I have a simple Flutter function to get a counter from shared preferences, increment it, and save it back to shared preferences. It's in a separate file because I'm going to add more code and call it from several screens. The problem is that the counter value does not persist when I restart the app. I suspect the issue is the scope of my counter variable, but I don't know how to fix it.

Here's my code:

import 'package:shared_preferences/shared_preferences.dart';

var fileName = 'Counter';
int counter;

updateCounter() {

  getCounter(counter) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    counter = (prefs.getInt('$fileName') ?? 0);
  }

  putCounter(counter) async {
    SharedPreferences preferences = await   SharedPreferences.getInstance();
    preferences.setInt('$fileName', counter);
    );
  }

  getCounter(counter);
  if (counter == null) {
    counter = 0;
  }
  counter++;
  putCounter(counter);

}

Answer 1

The problem appears to be with this method :

getCounter(counter) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    counter = (prefs.getInt('$fileName') ?? 0);
  }

It should be as follows:

int getCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    counter = (prefs.getInt('$fileName') ?? 0);
    return counter;
  }