app_permission.dart

class ScreenOne extends StatefulWidget {
  @override
  _ScreenOneState createState() => _ScreenOneState();
}

class _ScreenOneState extends State<ScreenOne> with WidgetsBindingObserver {
  String _platformVersion = 'Unknown';
  String _statusMessage = "waiting for camera permission";
  Permission permission;

  @override
  void initState() {
    super.initState();
    initPlatformState();
    WidgetsBinding.instance.addObserver(this);
    requestPermission();
  }

  initPlatformState() async {
    String platformVersion;
    try {
      platformVersion = await SimplePermissions.platformVersion;
    } on PlatformException {
      platformVersion = 'Failed to get platform version.';
    }
    if (!mounted) return;
    setState(() {
      _platformVersion = platformVersion;
    });
  }

  requestPermission() async {
    final res = await SimplePermissions.requestPermission(Permission.Camera);
  }

  checkPermission() async {
    bool res = await SimplePermissions.checkPermission(Permission.Camera);
    if (!res) {
      setState(() {
        _statusMessage = "waiting for camera permission";
      });
    } else {
      setState(() {
        _statusMessage = "camera permission has been granted";
      });
    }
  }

  getPermissionStatus() async {
    final res = await SimplePermissions.getPermissionStatus(Permission.Camera);
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    checkPermission();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        title: Text("Test page 1"),
      ),
      body: Center(
        child: Text(_statusMessage),
      ),
    );
  }
}