Progress view using flutter

Progressview.dart

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key key}) : super(key: key);

  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _index = 0;

  @override
  Widget build(BuildContext context) {
    return Stepper(
      type: StepperType.horizontal,
      controlsBuilder: (BuildContext buildContext, {void Function() onStepCancel, void Function() onStepContinue}) {
        return Row(
          children: <Widget>[
            TextButton(
              onPressed: onStepContinue,
              child: const Text('NEXT'),
            ),
            TextButton(
              onPressed: onStepCancel,
              child: const Text('CANCEL'),
            ),
          ],
        );
      },
      currentStep: _index,
      onStepCancel: () {
        if (_index > 0) {
          setState(() {
            _index -= 1;
          });
        }
      },
      onStepContinue: () {
        if (_index <= 0) {
          setState(() {
            _index += 1;
          });
        }
      },
      onStepTapped: (int index) {
        setState(() {
          _index = index;
        });
      },
      steps: <Step>[
        Step(
          title: const Text('Step 1 title'),
          content: Container(
            alignment: Alignment.centerLeft,
            child: const Text('Content for Step 1')
          ),
        ),
        const Step(
          title: Text('Step 2 title'),
          content: Text('Content for Step 2'),
        ),
        const Step(
          title: Text('Step 3 title'),
          content: Text('Content for Step 3'),
        ),
      ],
    );
  }
}


class StepProgressView extends StatelessWidget {

  StepProgressView({
    Key key,
    @required List<IconData> icons,
    @required int curStep,
    @required double width,
    @required Color color,
    List<String> titles
  }) :
      _icons = icons,
      _titles = titles,
      _curStep = curStep,
      _width = width,
      _activeColor = color,
      assert(curStep > 0 == true && curStep <= icons.length),
      assert(width > 0),
      super(key: key);

  final double _width;
  final List<IconData> _icons;
  final List<String> _titles;
  final int _curStep;
  final Color _activeColor;
  final Color _inactiveColor = Colors.grey[100];
  final double lineWidth = 4.0;

  Widget build (BuildContext context) {
    return Container(
      padding: EdgeInsets.only(top: 32.0, left: 24.0, right: 24.0,),
      width: this._width,
      child: Column(
        children: <Widget>[
          Row(
            children: _iconViews(),
          ),
          SizedBox(height: 10,),
          if (_titles != null)
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: _titleViews(),
            ),
        ])
    );
  }

  List<Widget> _iconViews() {
    final List<Widget> list = <Widget>[];

    _icons.asMap()
      .forEach((int i, IconData icon) {
      final Color circleColor = (i == 0 || _curStep > i + 1)
          ? _activeColor
          : _inactiveColor;

      final Color lineColor = _curStep > i + 1
          ? _activeColor
          : _inactiveColor;

      final Color iconColor = (i == 0 || _curStep > i + 1)
          ? _inactiveColor
          : _activeColor;

      list.add(
        //dot with icon view
        Container(
          width: 30.0,
          height: 30.0,
          padding: EdgeInsets.all(0),
          child: Icon(icon, color: iconColor,size: 15.0,),
          decoration: BoxDecoration(
            color: circleColor,
            borderRadius: BorderRadius.all(Radius.circular(25.0)),
            border: Border.all(
              color: _activeColor,
              width: 2.0,
            ),
          ),
        ),
      );

      //line between icons
      if (i != _icons.length - 1) {
        list.add(
          Expanded(
            child: Container(height: lineWidth, color: lineColor,)
          )
        );
      }
    });

    return list;
  }

  List<Widget> _titleViews() {
    final List<Widget> list = <Widget>[];

    _titles.asMap().forEach((int i, String text) {
      list.add(Text(text, style: TextStyle(color: _activeColor)));
    });

    return list;
  }
}