flutter本地缓存

```

_incrementCounter() async {

    SharedPreferences prefs = await SharedPreferences.getInstance();

    setState(() {

      countString = countString + " 1";

    });

    int counter = (prefs.getInt('counter') ?? 0) + 1;

    await prefs.setInt('counter', counter);

  }

  _getCounter() async {

    SharedPreferences prefs = await SharedPreferences.getInstance();

    setState(() {

      localCount = prefs.getInt('counter').toString();

    });

  }

```