How to add line dash in Flutter?

You can use path_drawing package and CustomPainter class:

Try this:

import 'package:flutter/material.dart';
import 'package:path_drawing/path_drawing.dart';

class DashedLinePainter extends CustomPainter {

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..color = Colors.orange
      ..strokeWidth = 5
      ..style = PaintingStyle.stroke
      ..strokeCap = StrokeCap.round;
    Path path = Path();

    path.moveTo(70, 170);
    path.arcToPoint(const Offset(120, 210), radius: const Radius.circular(20), clockwise: false);
    path.arcToPoint(const Offset(200, 300), radius: const Radius.circular(50));
    path.arcToPoint(const Offset(300, 400), radius: const Radius.circular(20), clockwise: false);

    canvas.drawPath(
      dashPath(
        path,
        dashArray: CircularIntervalList<double>(<double>[15.0, 10.5]),
      ),
      paint,
    );
  }

  @override
  bool shouldRepaint(DashedLinePainter oldDelegate) => false;

  @override
  bool shouldRebuildSemantics(DashedLinePainter oldDelegate) => false;
}

My result: