map_test.dart

import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';

class MapTest extends StatefulWidget {
  const MapTest({Key key}) : super(key: key);

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

class _MapTestState extends State<MapTest> {
  GoogleMapController _controller;
  bool swapBounds = true;

  var userLatLong = LatLng(26.462084, -80.07101);
  var merchantLatLong = LatLng(26.4846112, -80.064216);

  LatLngBounds getCurrentBounds(LatLng position1, LatLng position2) {
    LatLngBounds bounds;

    try {
      bounds = LatLngBounds(
        northeast: position1,
        southwest: position2,
      );
    } catch (_) {
      bounds = LatLngBounds(
        northeast: position2,
        southwest: position1,
      );
    }

    return bounds;
  }

  @override
  Widget build(BuildContext context) {
    var userCameraPosition = CameraPosition(
      target: userLatLong,
      zoom: 16.151926040649414,
    );

    return Scaffold(
      body: GoogleMap(
        onMapCreated: (controller) {
          if (_controller == null) {
            _controller = controller;
          }
        },
        mapType: MapType.terrain,
        initialCameraPosition: userCameraPosition,
        markers: Set.from([
          Marker(
            markerId: MarkerId('Your location'),
            position: userLatLong,
          ),
          Marker(
            markerId: MarkerId('Merchant Location'),
            position: merchantLatLong,
          ),
        ]),
        cameraTargetBounds:
            CameraTargetBounds(getCurrentBounds(userLatLong, merchantLatLong)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            swapBounds = !swapBounds;
            userLatLong = LatLng(26.462084, -80.07101);
            merchantLatLong = swapBounds
                ? LatLng(26.4636579, -80.07231829999999)
                : LatLng(26.4846112, -80.064216);

            updateMapToBounds(getCurrentBounds(userLatLong, merchantLatLong));
          });
        },
      ),
    );
  }

  Future updateMapToBounds(LatLngBounds bounds) async {
    await Future.delayed(Duration(milliseconds: 50));
    _controller.animateCamera(
      CameraUpdate.newLatLngBounds(bounds, 40),
    );
  }
}