BottomNavigation2

main.dart

import 'package:flutter/material.dart';

main() => runApp(MaterialApp(home: MyHomePage()));

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

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter4Fun.com'),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(18.0),
          child: MyBottomSheet(),
        ),
      ),
    );
  }

}

class MyBottomSheet extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: _MyBottomSheetCustomPainter(),
      size: Size(
        double.infinity,
        74,
      ),
    );
  }
}

class _MyBottomSheetCustomPainter extends CustomPainter {

  static final double holeWidth = 80;
  static final double holeWidthHalf = holeWidth / 2;
  static final double holeHeight = 30;

  final double targetXPercent;

  _MyBottomSheetCustomPainter({this.targetXPercent = 0.5});

  @override
  void paint(Canvas canvas, Size size) {
    Path p = new Path();

    final targetX = size.width * targetXPercent;

    final point0 = Offset(0, 0);
    p.moveTo(point0.dx, point0.dy);

    final point1 = Offset(targetX - holeWidthHalf, 0);
    p.lineTo(point1.dx, point1.dy);

    final point2 = Offset(targetX, holeHeight);

    final controlPoint1 = Offset(point1.dx + 24, 0);
    final controlPoint2 = Offset(point1.dx + 15, 28);

    p.cubicTo(
      controlPoint1.dx,
      controlPoint1.dy,
      controlPoint2.dx,
      controlPoint2.dy,
      point2.dx,
      point2.dy,
    );

    final point3 = Offset(targetX + holeWidthHalf, 0);
    final controlPoint3 = Offset(point3.dx - 15, 28);
    final controlPoint4 = Offset(point3.dx - 24, 0);

    p.cubicTo(
      controlPoint3.dx,
      controlPoint3.dy,
      controlPoint4.dx,
      controlPoint4.dy,
      point3.dx,
      point3.dy,
    );

    final point4 = Offset(size.width, 0);
    p.lineTo(point4.dx, point4.dy);

    canvas.drawPath(
      p,
      Paint()
        ..color = Colors.black
        ..style = PaintingStyle.stroke
        ..strokeWidth = 2);

    drawPoint(canvas, point0);
    drawPoint(canvas, point1);
    drawPoint(canvas, point2);
    drawPoint(canvas, point3);
    drawPoint(canvas, point4);
  }

  void drawPoint(Canvas canvas, Offset point) {
    canvas.drawCircle(point, 3, Paint()..color = Colors.black);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => true;
}