P11 - Flutter 2

Flutter - Aula 2

Código auxiliar para a aula 2 de Flutter

Step 1 - FutureBuilder

//Add the following method
Future<String> _fetchAnAsyncString() async {
  await Future.delayed(const Duration(seconds: 5));
  return Future.value('Hello world, from an aysnc call!');
}


//Inside the build method:
FutureBuilder<String>(
  future: _fetchAnAsyncString(),
  builder: (
	BuildContext context, AsyncSnapshot<String> snapshot
  ) {
    if (snapshot.hasData) {
      return Text(snapshot.data!);
    } else if (snapshot.hasError) {
      return const Text('Oops, something happened');
    } else {
      return const CircularProgressIndicator();
    }
  },
),

Step 2 - http

static const String _catFactsUrl = 'https://catfact.ninja/facts';

//inside the build method:
FutureBuilder<http.Response>(
  future: http.get(Uri.parse(_catFactsUrl)),
  builder: (
		BuildContext context,AsyncSnapshot<http.Response> snapshot
  ) {
    if (snapshot.hasData) {
      return Expanded(
                  child: SingleChildScrollView(
                               child: Text(snapshot.data!.body)
                         )
              );
    } else if (snapshot.hasError) {
      return const Text('Oops, something happened');
    } else {
      return const CircularProgressIndicator();
    }
  },
),

Step 3 - ListView - Cats

//outside any class:
class CatFact {
  CatFact.fromJson(Map<String, dynamic> json)
      : fact = json['fact'],
        length = json['length'];

  final String fact;
  final int length;
}


//inside the state:
List<CatFact>? _catFacts;
bool _fetchingData = false;

Future<void> _fetchCatFacts() async {
  try {
    setState(() => _fetchingData = true);

    http.Response response = await http.get(Uri.parse(_catFactsUrl));

    if (response.statusCode == HttpStatus.ok) { //import 'dart:io';
      debugPrint(response.body);
      final Map<String, dynamic> decodedData = json.decode(response.body);
      setState(() => _catFacts = (decodedData['data'] as List).map((fact) => CatFact.fromJson(fact)).toList());
    }
  } catch (ex) {
    debugPrint('Something went wrong: $ex');
  } finally {
    setState(() => _fetchingData = false);
  }
}

//inside the build method:
ElevatedButton(
  onPressed: _fetchCatFacts,
  child: const Text('Fetch cat facts'),
),
if (_fetchingData) const CircularProgressIndicator(),
if (!_fetchingData && _catFacts != null && _catFacts!.isNotEmpty)
  Expanded(
    child: ListView.separated(
      itemCount: _catFacts!.length,
      separatorBuilder: (_, __) => const Divider(thickness: 2.0),
      itemBuilder: (BuildContext context, int index) => ListTile(
        title: Text('Cat fact #$index'),
        subtitle: Text(_catFacts![index].fact),
      ),
    ),
  )

Step 4 - Image - asset

// Create an images directory in the project
// Place an image of your choice in the directory
// .../<flutter_prj_path>/images/xpto.jpg

//Add (at the end of the pubspec.yaml file; be careful with the indentation):
flutter:
   ...
   assets:
      - images/xpto.jpg

// before the first text in the Stateful Widget, add:
SizedBox(height:200, child: Image.asset('images/xpto.jpg'))

Step 5 - Image - network

static const String _ipc_logo = 'https://wayf.ipc.pt/IPCds/images/logo_ipc2.png';

//after or replacing the previous image:
SizedBox(height:50, child: Image.network(_ipc_logo)),

Step 6 - Textediting

//Comment the _incrementCounter method and add:
int _inc=1;
void changeInc(int inc) { setState(() {_inc = inc;}); }
void _incrementCounter() { setState(() {_counter+=_inc; }); }
  
//insert in the build method:
TextField(
    decoration: const InputDecoration(
      labelText: 'Increment:',
      hintText: 'Value to increment',
    ),
    onChanged: (value) => changeInc(int.tryParse(value) ?? 1),
),

Step 7 - Shared Preferences

//first: include the shared_preferences plugin

@override
void initState() {
    super.initState();
    initCounter();
}

Future<void> initCounter() async {
    var prefs = await SharedPreferences.getInstance();
    setState (() { _counter = prefs.getInt ('counter') ?? 1; } );
}

void _incrementCounter() async {
    setState (() { _counter++; } );
    var prefs = await SharedPreferences.getInstance();
    await prefs.setInt('counter', _counter);
}

Step 8a - Location

//first: include the location plugin

//Change the kotlin version in the project build.gradle: ext.kotlin_version = '1.9.0'

//include permissions in the manifest file
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
    <uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION"/>

//include in the state class:

  Location location = Location();

  bool _serviceEnabled = false;
  PermissionStatus _permissionGranted = PermissionStatus.denied;
  LocationData _locationData = LocationData.fromMap({
    "latitude": 40.192639,
    "longitude": -8.411899,
  });

  void getLocation() async {
    _serviceEnabled = await location.serviceEnabled();
    if (!_serviceEnabled) {
      _serviceEnabled = await location.requestService();
      if (!_serviceEnabled) {
        return;
      }
    }

    _permissionGranted = await location.hasPermission();
    if (_permissionGranted == PermissionStatus.denied) {
      _permissionGranted = await location.requestPermission();
      if (_permissionGranted != PermissionStatus.granted) {
        return;
      }
    }
    _locationData = await location.getLocation();
    setState(() { });
  }

//include in the build method:
Text('Latitude: ${_locationData.latitude}; Longitude: ${_locationData.longitude}'),
ElevatedButton(onPressed: getLocation, child: const Text("Refresh")),

Step 8b - onLocationChange

// automatic updates

  StreamSubscription<LocationData>? _locationSubscription;
  
  void startLocationUpdates() {
    _locationSubscription=location.onLocationChanged.listen((LocationData currentLocation) {
      setState(() {_locationData = currentLocation;});
    });
  }

  void stopLocationUpdates() {
    _locationSubscription?.cancel();
    _locationSubscription=null;
  }


//include in the build method:
ElevatedButton(onPressed: startLocationUpdates, child: const Text("Start")),
ElevatedButton(onPressed: stopLocationUpdates, child: const Text("Stop")),

StreamBuilder(
    stream: location.onLocationChanged,
    builder: (context,snapshot) {
        if (snapshot.hasData) {
            return Text(
                'LatitudeB: ${snapshot.data!.latitude}; '
                'LongitudeB: ${snapshot.data!.longitude}'
            );
        }
        return const CircularProgressIndicator();
    }
),

Step 9 - Firebase

//pubspec.yaml
firebase_core: any
cloud_firestore: any

-- *** --

// main.dart
//....
import 'package:firebase_core/firebase_core.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'firebase_options.dart';

void initFirebase() async {
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );

}

void main() {
  // Ensure that Flutter is initialized before Firebase
  WidgetsFlutterBinding.ensureInitialized();
  initFirebase();
  runApp(const MyApp());
}

//...

-- *** --
String? _error;

void addFirebase() async {
  var db = FirebaseFirestore.instance;
  var document = db.collection('MyColl').doc("MyDocAMOV");
  await document.set({
    'subject': 'Mobile Architectures',
    'nrStudents': 0}
  ).onError(
          (error, stackTrace) {
        setState(() {_error = error.toString();});
      });

  setState(() {
    _error = null;
  });
}

void delFirebase() async {
  var db = FirebaseFirestore.instance;
  var document = db.collection('MyColl').doc("MyDocAMOV");
  await document.delete().onError(
          (error, stackTrace) {
        setState(() {_error = error.toString();});
        debugPrint('Error!!!');
      });

  setState(() {
    _error = null;
  });
}

void updateFirebase() async {
  var db = FirebaseFirestore.instance;
  var document = db.collection('MyColl').doc("MyDocAMOV");
  var data = await document.get(const GetOptions(source: Source.server));
  if (data.exists) {
    var nrStudents = data['nrStudents'] + 1;
    document.update({'nrStudents': nrStudents}).then(
            (res) => setState(() { _error = null; }),
        onError: (e) => setState(() { _error = e.toString();})
    );
  } else {
    setState(() { _error = "Document doesn't exist";});
  }
}


void listDocuments() async {
  var db = FirebaseFirestore.instance;
  var collection = await db.collection('MyColl').get();
  for(var doc in collection.docs) {
    debugPrint("Doc: ${doc.id}"); //doc.data()...
  }
}

-- *** --

//inside the build method:
    if (_error != null) Text("Error: $_error"),
    ElevatedButton(
      onPressed: addFirebase,
      child: const Text('Add document'),
    ),
    ElevatedButton(
      onPressed: delFirebase,
      child: const Text('Del document'),
    ),
    ElevatedButton(
      onPressed: updateFirebase,
      child: const Text('Update document'),
    ),