Adding Shared Preferences To App4

1. Installing

Run this command:

flutter pub add shared_preferences

This will add a line like this to your package's pubspec.yaml (and run an implicit flutter pub get):

dependencies:
     shared_preferences: ^2.0.9

Or visit shared_preferences - pub.dev

Now run pub get from the command line:

flutter pub get

You’re now ready to store data.



2. Import the package in the main



import 'package:shared_preferences/shared_preferences.dart';






3. Create a key

All preferences need to use a unique key or they’ll be overwritten. Here, you’re simply defining a constant for the preference key.

 static const String bestScorekey = 'bestScore';




4. Saving The Best Score

To understand the code you’ll add next, you need to know a bit about running code in the background.

Most modern UIs have a main thread that runs the UI code. Any code that takes a long time needs to run on a different thread or process so it doesn’t block the UI.
Dart uses a technique similar to JavaScript to achieve this. The language includes these two keywords:

• async
• await

Check these lessons :

     Handling Futures

     Declaring async funtions

  void saveNewBestScore(int value) async {

    //1

    final prefs = await SharedPreferences.getInstance();

    //2

    prefs.setInt(bestScorekey, value);

  }







Here, you use the async keyword to indicate that this method will run asynchronously. It also:

1. Uses the await keyword to wait for an instance of SharedPreferences.

2. Saves the best score using the prefSearchKey key.

Next, call it in the check answer method:

  void checkAnswer() {

    if (answer == correctCountry) {

      setState(() {

        score++;

        prepareCountries();

      });

    } else {

      if (score > bestScore) {

        bestScore = score;

        ///add this here

        saveNewBestScore(score);

      }

 

      setState(() {

        playing = false;

      });

      prepareCountries();

    }

  }






5. Getting The Best Score



  void getBestScore() async {

    //1

    final prefs = await SharedPreferences.getInstance();

    //2

    if (prefs.containsKey(bestScorekey)) {

      //3

      bestScore = prefs.getInt(bestScorekey);

    }

  }







This method is also asynchronous. Here, you:

1. Use the await keyword to wait for an instance of SharedPreferences.

2. Check if a preference for the best score already exists.

3. Get the best score.


Finally, right after super.initState() in initState() call it:

  @override

  void initState() {

    super.initState();

    prepareCountries();

    getBestScore();

  }







This loads the previous best score when the user restarts the app.




6. Test the app




7. Code Source