A quick guide: obtaining current location on Google Maps using Riverpod in Flutter

#flutter #riverpod #beginners #googlecloud

Goal: Get the current location and set a marker

Hi everyone! This article will look at how we get the current location of the user and set a marker as being a specific location on Flutter. This app has several features as shown below.

Show Google Map by google_maps_flutter
Obtain the current location
Set the marker and shift for it after pushing the bottom right button

Get API key

At first, let's obtain your API key for Google Maps.

Fix AndroidManifest.xml

android/app/src/main/AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.googlemap.testgooglemap">     // Add this     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />   <application        android:label="testgooglemap"        android:icon="@mipmap/ic_launcher">                // Add this                <meta-data          android:name="com.google.android.geo.API_KEY"          android:value="<YOUR API KEY>" />        ...    </application></manifest>

Modify AppDelegate.swift

ios/Runner/AppDelegate.swift

importUIKitimportFlutterimportGoogleMaps@UIApplicationMain@objcclassAppDelegate:FlutterAppDelegate{overridefuncapplication(_application:UIApplication,didFinishLaunchingWithOptionslaunchOptions:[UIApplication.LaunchOptionsKey:Any]?)->Bool{GMSServices.provideAPIKey("<YOUR API KEY>")GeneratedPluginRegistrant.register(with:self)returnsuper.application(application,didFinishLaunchingWithOptions:launchOptions)}}

Add a key in Info.plist

To show a dialog to allow the user gives the current location to app, put a pair of key and description intoInfo.plist .

ios/Runner/Info.plist

<dict><key>NSLocationWhenInUseUsageDescription</key><string>Yourlocationisrequiredforthisapp</string>...</dict>

Upgrade minSdkVersion in build.gradle

You have to make minSdkVersion going up to 20 from 16 for working out well this app on google_maps_flutter package. In my case, I also had to fix compileSdkVersion to 31.

google_maps_flutter | Flutter Package

android{compileSdkVersion31// up to 31 from 30...defaultConfig{// TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).applicationId"com.googlemap.testgooglemap"minSdkVersion20// up to 20 from 16targetSdkVersion30versionCodeflutterVersionCode.toInteger()versionNameflutterVersionName}

pubspec.yaml

dependencies:flutter:sdk:fluttercupertino_icons:^1.0.2google_maps_flutter:^2.1.1geolocator:^8.0.0riverpod:^1.0.0flutter_hooks:^0.18.0hooks_riverpod:^1.0.0http:^0.13.4freezed_annotation:^1.0.0json_annotation:^4.3.0flutter_secure_storage:^5.0.1geocoding:^2.0.1dev_dependencies:flutter_test:sdk:flutterfreezed:^1.0.0build_runner:^2.1.5json_serializable:^6.0.1

main.dart

Let's modify your code in main.dart. Some errors would be shown on your text editor when pasting it, but don't have to be careful about that for now. We'll fix it up by adding other code.

lib/main.dart

import'package:flutter/material.dart';import'package:hooks_riverpod/hooks_riverpod.dart';import'/models/controllers/location/location_controller.dart';import'package:flutter_hooks/flutter_hooks.dart';import'package:google_maps_flutter/google_maps_flutter.dart';import'dart:async';voidmain(){runApp(ProviderScope(child:MyApp(),));}classMyAppextendsStatelessWidget{// This widget is the root of your application.@overrideWidgetbuild(BuildContextcontext){returnMaterialApp(title:'Flutter Demo',theme:ThemeData(primarySwatch:Colors.blue,),home:constHomepage(),);}}classHomepageextendsHookConsumerWidget{constHomepage({Key?key}):super(key:key);@overrideWidgetbuild(BuildContextcontext,WidgetRefref){finallocationState=ref.watch(locationNotifierProvider);finallocationNotifier=ref.watch(locationNotifierProvider.notifier);useEffect((){Future.microtask(()async{ref.watch(locationNotifierProvider.notifier).getCurrentLocation();});return;},const[]);returnScaffold(body:locationState.isBusy?constCenter(child:CircularProgressIndicator()):GoogleMap(mapType:MapType.normal,myLocationButtonEnabled:true,myLocationEnabled:true,zoomControlsEnabled:false,initialCameraPosition:CameraPosition(target:locationState.currentLocation,zoom:14.4746,),markers:locationState.markers,onMapCreated:locationNotifier.onMapCreated,),floatingActionButton:FloatingActionButton(onPressed:()async{locationNotifier.getNewLocation();},child:constIcon(Icons.location_searching)));}}

Let's take a look at that. We can handle the state on Flutter by Riverpod. In this sample app,locationState for reading state andlocationNotifier for changing state are defined.

@overrideWidgetbuild(BuildContextcontext,WidgetRefref){finallocationState=ref.watch(locationNotifierProvider);finallocationNotifier=ref.watch(locationNotifierProvider.notifier);

useEffect is useful to initialize something on every build. In here's sample, we call thegetCurrentLocatoin() function defined in location_controller.dart for state management.

useEffect((){Future.microtask(()async{locationNotifier.getCurrentLocation();});return;},const[]);

When user presses the bottom right button,FloatingActionButton() callgetNewLocation() function that shifts the position of camera and sets a pin.

floatingActionButton:FloatingActionButton(onPressed:()async{locationNotifier.getNewLocation();},child:constIcon(Icons.location_searching)));

LocationController

As you can see, LocationController extends StateNotifier class.

lib/models/controllers/location/location_controller.dart

import'package:google_maps_flutter/google_maps_flutter.dart';import'package:riverpod/riverpod.dart';import'package:hooks_riverpod/hooks_riverpod.dart';import'package:flutter/material.dart';import'/models/repositories/location/location_repository.dart';import'/models/controllers/location/location_state.dart';import'dart:async';finallocationNotifierProvider=StateNotifierProvider<LocationController,LocationState>((ref)=>LocationController(),);classLocationControllerextendsStateNotifier<LocationState>{LocationController():super(constLocationState());finalrepository=LocationRepository();finalCompleter<GoogleMapController>_mapController=Completer();voidonMapCreated(GoogleMapControllercontroller){_mapController.complete(controller);}Future<void>getCurrentLocation()async{state=state.copyWith(isBusy:true);try{finaldata=awaitrepository.getCurrentPosition();state=state.copyWith(isBusy:false,currentLocation:LatLng(data.latitude,data.longitude));}onExceptioncatch(e,s){debugPrint('login error:$e - stack:$s');state=state.copyWith(isBusy:false,errorMessage:e.toString());}}Future<void>getNewLocation()async{await_setNewLocation();await_setMaker();}Future<void>_setNewLocation()async{state=state.copyWith(newLocation:constLatLng(35.658034,139.701636));}Future<void>_setMaker()async{// Set markersfinalSet<Marker>_markers={};_markers.add(Marker(markerId:MarkerId(state.newLocation.toString()),position:state.newLocation,infoWindow:constInfoWindow(title:'Remember Here',snippet:'good place'),icon:BitmapDescriptor.defaultMarker));state=state.copyWith(markers:_markers);// Shift camera positionCameraPosition_kLake=CameraPosition(target:state.newLocation,zoom:14.4746);finalGoogleMapControllercontroller=await_mapController.future;controller.animateCamera(CameraUpdate.newCameraPosition(_kLake));}}

LocationController defines three functions to call from main.dart.

voidonMapCreated(GoogleMapControllercontroller){}Future<void>getCurrentLocation()async{}Future<void>getNewLocation()async{}

Freezed for controller

This sample app uses Freezed package, making the data immutable easily. This is used for LocationController.

lib/models/controllers/location/location_state.dart

import'package:freezed_annotation/freezed_annotation.dart';import'package:flutter/foundation.dart';import'package:google_maps_flutter/google_maps_flutter.dart';part'location_state.freezed.dart';@freezedclassLocationStatewith_$LocationState{constfactoryLocationState({@Default(false)boolisBusy,@Default(LatLng(35.658034,139.701636))LatLngcurrentLocation,@Default(LatLng(35.658034,139.701636))LatLngnewLocation,@Default({})Set<Marker>markers,String?errorMessage,})=_LocationState;}

Run the following command with build_runner.

$flutter pub run build_runner build--delete-conflicting-outputs

Repository class for the error handling

We'll also set upgetCurrentPosition() in LocationRepository class, the function to handle errors on the permission regarding the location.

lib/models/repositories/location/location_repository.dart

import'package:geolocator/geolocator.dart';
classLocationRepository{
Future<Position>getCurrentPosition()async{
boolserviceEnabled;
LocationPermissionpermission;
<span>serviceEnabled</span> <span>=</span> <span>await</span> <span>Geolocator</span><span>.</span><span>isLocationServiceEnabled</span><span>();</span><span>if</span> <span>(</span><span>!</span><span>serviceEnabled</span><span>)</span> <span>{</span>  <span>return</span> <span>Future</span><span>.</span><span>error</span><span>(</span><span>'Location services are disabled.'</span><span>);</span><span>}</span><span>permission</span> <span>=</span> <span>await</span> <span>Geolocator</span><span>.</span><span>checkPermission</span><span>();</span><span>if</span> <span>(</span><span>permission</span> <span>==</span> <span>LocationPermission</span><span>.</span><span>denied</span><span>)</span> <span>{</span>  <span>permission</span> <span>=</span> <span>await</span> <span>Geolocator</span><span>.</span><span>requestPermission</span><span>();</span>  <span>if</span> <span>(</span><span>permission</span> <span>==</span> <span>LocationPermission</span><span>.</span><span>denied</span><span>)</span> <span>{</span>    <span>return</span> <span>Future</span><span>.</span><span>error</span><span>(</span><span>'Location permissions are denied'</span><span>);</span>  <span>}</span><span>}</span><span>if</span> <span>(</span><span>permission</span> <span>==</span> <span>LocationPermission</span><span>.</span><span>deniedForever</span><span>)</span> <span>{</span>  <span>return</span> <span>Future</span><span>.</span><span>error</span><span>(</span>      <span>'Location permissions are permanently denied, we cannot request permissions.'</span><span>);</span><span>}</span><span>return</span> <span>await</span> <span>Geolocator</span><span>.</span><span>getCurrentPosition</span><span>(</span>    <span>desiredAccuracy:</span> <span>LocationAccuracy</span><span>.</span><span>high</span><span>);</span>
}
}