颤振如何检查拉绳是否已完全拉出

Question

此代码适用于黑屏的应用程序。它允许用户用黑色绘制它，它给了他们20秒的时间，用手指将屏幕变成白色。我想自动检查屏幕是否全部为白色。

class tactilee extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: MyHomePage());
  }
}

class DrawingArea {
  Offset point;
  Paint areaPaint;

  DrawingArea({this.point, this.areaPaint});
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<DrawingArea> points = [];
  Color selectedColor;
  double strokeWidth;
  @override
  void initState() {
    super.initState();
    new Future.delayed(Duration (seconds: 20), () {
    //check if alll in white
    });

    selectedColor = Colors.white;
    strokeWidth = 70.0;
    SystemChrome.setEnabledSystemUIOverlays([]);
  }

  @override
  Widget build(BuildContext context) {
    return Builder(
        builder: (context) => Container(
            child: Stack(
              children: <Widget>[
                Container(
                    decoration: BoxDecoration(boxShadow: []),
                    child: GestureDetector(
                      onPanDown: (details) {
                        this.setState(() {
                          points.add(DrawingArea(
                              point: details.localPosition,
                              areaPaint: Paint()
                                ..strokeCap = StrokeCap.round
                                ..isAntiAlias = true
                                ..color = selectedColor
                                ..strokeWidth = strokeWidth));
                        });
                      },
                      onPanUpdate: (details) {
                        this.setState(() {
                          points.add(DrawingArea(
                              point: details.localPosition,
                              areaPaint: Paint()
                                ..strokeCap = StrokeCap.round
                                ..isAntiAlias = true
                                ..color = selectedColor
                                ..strokeWidth = strokeWidth));
                        });
                      },
                      onPanEnd: (details) {
                        this.setState(() {
                          points.add(null);
                        });
                      },
                      child: SizedBox.expand(
                        child: ClipRRect(
                          borderRadius: BorderRadius.all(Radius.circular(20.0)),
                          child: CustomPaint(
                            painter: MyCustomPainter(points: points),
                          ),
                        ),
                      ),
                    ),
                  )
              ],
            )));
  }
}

class MyCustomPainter extends CustomPainter {
  List<DrawingArea> points;

  MyCustomPainter({@required this.points});

  @override
  void paint(Canvas canvas, Size size) {
    Paint background = Paint()..color = Colors.black;
    Rect rect = Rect.fromLTWH(0, 0, size.width, size.height);
    canvas.drawRect(rect, background);
    canvas.clipRect(rect);

    for (int x = 0; x < points.length - 1; x++) {
      if (points[x] != null && points[x + 1] != null) {
        canvas.drawLine(
            points[x].point, points[x + 1].point, points[x].areaPaint);
      } else if (points[x] != null && points[x + 1] == null) {
        canvas.drawPoints(
            PointMode.points, [points[x].point], points[x].areaPaint);
      }
    }
  }

  @override
  bool shouldRepaint(MyCustomPainter oldDelegate) {
    return oldDelegate.points != points;
  }
}

这是画家在容器内的代码，并且有一个工作的计时器。 20秒后，我想在此计时器内检查容器被触摸后是否全部为白色。