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Lesson 4 - Food Finder: Google Maps & URL Launcher

We are implementing a very basic version of Yelp in this lesson. You will learn about how to integrate Google Maps and open website urls in your Flutter app!

Part 1 - Get the Google Maps API Key

Navigate your web browser to Google Cloud Maps Platform

Click get started

Select Maps and click continue

If you see this error msg, switch to a non-usc email address and try again.

Create a new project, give it a name, agree to Google's Terms of Service, and click next

You might need to setup your billing information with your credit/debit card. You also get $300 credits for free! If you don't have a credit/debit card, ask me for an API key.

After your billing account has been setup, click next to create your key! You Google Maps API key should be displayed on the next screen.

Part 2 - Integrate Google Map

Now we can install Google Maps plugin to our flutter app and define our API key.

Start by creating a new Flutter project in your Android Studio

In your pubspec.yaml, add the following as an entry under dependencies.

google_maps_flutter: ^0.2.0+3

Near the top of your editor, click the blue text Packages get to install the newly added google_maps_flutter package

After google_maps_flutter has been installed, we should add our API key. The API key needs to be defined for android and iOS separately depending on which platform you want to use.

Android

Open android/app/src/main/AndroidManifest.xml Add the following just above/before </application>

<meta-data android:name="com.google.android.geo.API_KEY"
            android:value="YOUR GOOGLE MAPS API KEY"/>

iOS

Open ios/Runner/AppDelegate.m, add

#import "GoogleMaps/GoogleMaps.h"

just below

#include "GeneratedPluginRegistrant.h"

And then also add

[GMSServices provideAPIKey:@"YOUR GOOGLE MAPS API KEY"];

just above

[GeneratedPluginRegistrant registerWithRegistry:self];

Finally, open ios/Runner/Info.plist and add

<key>io.flutter.embedded_views_preview</key>
<string>YES</string>

just above </dict>

Now you can finally add the Google Maps widget in your Flutter app!

Part 3 - Add restaurants display

In lib/main.dart, replace everything with the following

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Food Finder',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}

Let's import google_maps_flutter with

import 'package:google_maps_flutter/google_maps_flutter.dart';

Define our MyHomePage class

class MyHomePage extends StatelessWidget {
  GoogleMapController mapController;

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GoogleMap(
        onMapCreated: _onMapCreated,
        initialCameraPosition: const CameraPosition(
          target: LatLng(34.021574, -118.286659),
          zoom: 15,
        ),
      ),
    );
  }
}

MyHomePage class creates a GoogleMap widget in a Scaffold. We also defined an initial position and zoom for our map's camera.

Run your app, and you should see a Google Map centered at USC on the screen!

Let's add a floating action button in our app. Add the following below body of Scaffold in the build function of MyHomePage

floatingActionButton: FloatingActionButton(
  onPressed: () => {},
  child: Icon(Icons.restaurant),
),

Right now the button shows on the screen at bottom right, but it doesn't do anything yet. Let's work on that by adding some restaurants data.

Create Restaurant class after MyHomePage class:

class Restaurant {
  final String name, desc, url;
  final double lat, lng, zoom;

  Restaurant({this.name, this.desc, this.url, this.lat, this.lng, this.zoom});
}

Define a list of restaurants as a member variable of MyHomePage class:

RestauranList<Restaurant> restaurants = [
  Restaurant(
    name: "Panda Express",
    desc: "Panda Express at The Ronald Tutor Campus Center features USC’s acclaimed and award-winning modern Chinese cuisine. Reflective of USC's passion for Asian ingredients and cooking techniques, the cuisine is accompanied by polished service, opulent, contemporary décor and spectacular campus panoramas",
    url: "https://www.pandaexpress.com/",
    lat: 34.020519,
    lng: -118.286339,
    zoom: 15
  ),
  Restaurant(
    name: "Honeybird",
    desc: "Sunny, streamlined spot for buttermilk-brined fried chicken, plus salads, side dishes & mini pies.",
    url: "https://www.honeybirdla.com/",
    lat: 34.024744,
    lng: -118.284417,
    zoom: 15
  ),
  Restaurant(
      name: "Cava",
      desc: "CAVA is a growing Mediterranean culinary brand with a flavorful and healthy fast-casual restaurant experience featuring customizable & craveable salads, grain bowls, pitas, and house-made juices. CAVA’s chef-crafted dips and spreads are available at Whole Foods Market and other specialty markets across the country.",
      url: "https://cava.com/",
      lat: 34.024902,
      lng: -118.284582,
      zoom: 15
  ),
  Restaurant(
      name: "Chick-fil-A",
      desc: "Fast-food chain serving chicken sandwiches, strips & nuggets along with salads & sides.",
      url: "http://www.chick-fil-a.com/usc",
      lat: 34.016617,
      lng: -118.282555,
      zoom: 15
  ),
];

Also define a Marker variable and an int in MyHomePage to track the current restaurant data we are using

Marker markerPrev;
int currRestaurant;

We are going to be using states in MyHomePage, so convert the class to a StatefulWidget (Hover your cursor on MyHomePage, click the light bulb, and then click Convert to StatefulWidget)

Next, define a function in MyHomePageState

void _showRandomRestaurant() async {
  this.setState(() {
    final _random = new Random();
    int next = 0;
    while((next = _random.nextInt(this.restaurants.length)) == this.currRestaurant);
    this.currRestaurant = next;
  });

  var r = this.restaurants[this.currRestaurant];
  this.mapController.animateCamera(
    CameraUpdate.newLatLngZoom(
      LatLng(r.lat, r.lng),
      r.zoom,
    ),
  );
  var marker = await this.mapController.addMarker(MarkerOptions(
    position: LatLng(r.lat, r.lng),
    visible: true,
    //infoWindowText: InfoWindowText(r.name, r.desc),
  ));
  if (this.markerPrev != null) {
    this.mapController.removeMarker(this.markerPrev);
  }
  this.markerPrev = marker;
}

and connect it to the floating action button we created earlier

floatingActionButton: FloatingActionButton(
  onPressed: _showRandomRestaurant,
  child: Icon(Icons.restaurant),
),

To make it work, we also need to import dart's math library

import 'dart:math';

Everything should be self-explanatory. When the user taps on the floating action button, we randomly select a restaurant from our list, animate the map's camera to the location of the restaurant, and add a marker to the screen. If a previous marker exists, we want to remove it.

Unfortunately, support for marker label in google_maps_flutter is unstable, so we need to make our own labels to display some basic restaurant information.

Add the following function in MyHomePageState class

Widget _buildInfoCard(BuildContext context) {
  return this.currRestaurant == null ? Container() : SafeArea(
    child: Container(
      width: double.infinity,
      padding: EdgeInsets.all(30.0),
      child: Card(
        child: Container(
          padding: EdgeInsets.fromLTRB(15, 15, 15, 0),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Text(
                this.restaurants[this.currRestaurant].name,
                style: TextStyle(
                  fontSize: 30,
                  fontWeight: FontWeight.w600,
                ),
              ),
              Container(
                height: 10,
              ),
              Text(
                this.restaurants[this.currRestaurant].desc,
              ),
              ButtonTheme.bar(
                child: ButtonBar(
                  children: <Widget>[
                    FlatButton(
                      child: const Text('WEBSITE'),
                      onPressed: () { },
                    ),
                  ],
                ),
              ),
            ]
          ),
        ),
      ),
    ),
  );
}

Also change the body of our Scaffold to

Stack(
  children: [
    GoogleMap(
      onMapCreated: _onMapCreated,
      initialCameraPosition: const CameraPosition(
        target: LatLng(34.021574, -118.286659),
        zoom: 15,
      ),
    ),
    _buildInfoCard(context),
  ],
),

Now whenever a restaurant has been chosen, we also display its data on the screen!

Part 4 - Integrate URL Launcher

Congratulations, you have reached the easiest part of this lesson. Right now, if you tap on website on the restaurant info card, it does nothing. We want to make it open a link in the web browser on tap.

You should know how to install packages by now. Try installing url_launcher

url_launcher: ^5.0.1

Don't forget to import it in main.dart

import 'package:url_launcher/url_launcher.dart';

Define the url launching function in MyHomePageState class

_launchURL(url) async {
  if (await canLaunch(url)) {
    await launch(url);
  } else {
    throw 'Could not launch $url';
  }
}

Finally, redefine the onPressed button for our website link. Can you find where that is?

onPressed: () { _launchURL(this.restaurants[this.currRestaurant].url); },

All done! You now have a working mini yelp app 😃! If you still can't get it to work, please ask us for help! As always, the finished code is in the finished-code folder. However, you still need to fill-in the Google Maps API Key in the configuration files (The property is defined, but not the actual key).

Bonus Challenges

  • Figure out how to use the satellite map view
  • Add more restaurants?
  • Add a drawer in Scaffold to display all the available restaurants