Flutter:我想访问setstate的更改后的值，当我访问它时，它不会显示新的状态值

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });

    // 在setState的回调函数中访问更改后的值
    WidgetsBinding.instance.addPostFrameCallback((_) {
      print(_counter);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '$_counter',
              style: TextStyle(fontSize: 24),
            ),
            RaisedButton(
              onPressed: _incrementCounter,
              child: Text('Increment'),
            ),
          ],
        ),
      ),
    );
  }
}