Flutter - The getter 'value' was called on null - flutter

Question

I'm trying to save to SharedPreferences the current camera selected. When the app restarts, I would like the same camera to be used initially. If the user toggles to another camera, that camera gets saved.
When I have the following code in the initState, I get the "The getter 'value' was called on null." error message. Also the red/yellow error messages show up and disappear quickly before the camera starts working.
#override
void initState() {
try {
SharedPreferencesHelper prefs = SharedPreferencesHelper();
prefs.getCameraSelected().then((String answer) {
if (answer != null) {
if (answer == 'back') {
onCameraSelected(widget.cameras[0]);
} else {
onCameraSelected(widget.cameras[1]);
}
} else {
print('answer is null');
onCameraSelected(widget.cameras[1]);
}
});
} catch (e) {
print(e.toString());
}
super.initState();
}
If I replace the initState back to the original state, everything works as expected
#override
void initState() {
try {
onCameraSelected(widget.cameras[0]);
} catch (e) {
print(e.toString());
}
super.initState();
}
Below is the full code for the CameraHomeScreen.dart file:
import 'dart:async';
import 'dart:io';
import 'package:camera/camera.dart';
import 'package:path_provider/path_provider.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
class CameraHomeScreen extends StatefulWidget {
List<CameraDescription> cameras;
CameraHomeScreen(this.cameras);
#override
State<StatefulWidget> createState() {
return _CameraHomeScreenState();
}
}
class _CameraHomeScreenState extends State<CameraHomeScreen> {
String imagePath;
bool _toggleCamera = false;
String _currentCamera = 'back';
CameraController controller;
#override
void initState() {
try {
SharedPreferencesHelper prefs = SharedPreferencesHelper();
prefs.getCameraSelected().then((String answer) {
if (answer != null) {
print('here');
print(answer);
if (answer == 'back') {
onCameraSelected(widget.cameras[0]);
} else {
onCameraSelected(widget.cameras[1]);
}
} else {
print('answer is null');
onCameraSelected(widget.cameras[1]);
}
});
} catch (e) {
print(e.toString());
}
super.initState();
}
#override
void dispose() {
controller?.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
if (widget.cameras.isEmpty) {
return Container(
alignment: Alignment.center,
padding: EdgeInsets.all(16.0),
child: Text(
'No Camera Found',
style: TextStyle(
fontSize: 16.0,
color: Colors.white,
),
),
);
}
if (!controller.value.isInitialized) {
return Container();
}
return AspectRatio(
aspectRatio: controller.value.aspectRatio,
child: Container(
child: Stack(
children: <Widget>[
CameraPreview(controller),
Align(
alignment: Alignment.bottomCenter,
child: Container(
width: double.infinity,
height: 120.0,
padding: EdgeInsets.all(20.0),
color: Color.fromRGBO(00, 00, 00, 0.7),
child: Stack(
children: <Widget>[
Align(
alignment: Alignment.center,
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(Radius.circular(50.0)),
onTap: () {
_captureImage();
},
child: Container(
padding: EdgeInsets.all(4.0),
child: Image.asset(
'assets/images/ic_shutter_1.png',
width: 72.0,
height: 72.0,
),
),
),
),
),
Align(
alignment: Alignment.centerRight,
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(Radius.circular(50.0)),
onTap: () {
if (!_toggleCamera) {
SharedPreferencesHelper prefs =
SharedPreferencesHelper();
prefs.setCameraSelected('front');
onCameraSelected(widget.cameras[1]);
setState(() {
_toggleCamera = true;
});
} else {
SharedPreferencesHelper prefs =
SharedPreferencesHelper();
prefs.setCameraSelected('back');
onCameraSelected(widget.cameras[0]);
setState(() {
_toggleCamera = false;
});
}
},
child: Container(
padding: EdgeInsets.all(4.0),
child: Image.asset(
'assets/images/ic_switch_camera_3.png',
color: Colors.grey[200],
width: 42.0,
height: 42.0,
),
),
),
),
),
],
),
),
),
],
),
),
);
}
void onCameraSelected(CameraDescription cameraDescription) async {
if (controller != null) await controller.dispose();
controller = CameraController(cameraDescription, ResolutionPreset.medium);
controller.addListener(() {
if (mounted) setState(() {});
if (controller.value.hasError) {
showMessage('Camera Error: ${controller.value.errorDescription}');
}
});
try {
await controller.initialize();
} on CameraException catch (e) {
showException(e);
}
if (mounted) setState(() {});
}
String timestamp() => new DateTime.now().millisecondsSinceEpoch.toString();
void _captureImage() {
takePicture().then((String filePath) {
if (mounted) {
setState(() {
imagePath = filePath;
});
if (filePath != null) {
showMessage('Picture saved to $filePath');
setCameraResult();
}
}
});
}
void setCameraResult() {
Navigator.pop(context, imagePath);
}
Future<String> takePicture() async {
if (!controller.value.isInitialized) {
showMessage('Error: select a camera first.');
return null;
}
final Directory extDir = await getApplicationDocumentsDirectory();
final String dirPath = '${extDir.path}/FlutterDevs/Camera/Images';
await new Directory(dirPath).create(recursive: true);
final String filePath = '$dirPath/${timestamp()}.jpg';
if (controller.value.isTakingPicture) {
// A capture is already pending, do nothing.
return null;
}
try {
await controller.takePicture(filePath);
} on CameraException catch (e) {
showException(e);
return null;
}
return filePath;
}
void showException(CameraException e) {
logError(e.code, e.description);
showMessage('Error: ${e.code}\n${e.description}');
}
void showMessage(String message) {
print(message);
}
void logError(String code, String message) =>
print('Error: $code\nMessage: $message');
}
class SharedPreferencesHelper {
///
/// Instantiation of the SharedPreferences library
///
final String _nameKey = "cameraSelected";
/// ------------------------------------------------------------
/// Method that returns the user decision on sorting order
/// ------------------------------------------------------------
Future<String> getCameraSelected() async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.getString(_nameKey) ?? 'name';
}
/// ----------------------------------------------------------
/// Method that saves the user decision on sorting order
/// ----------------------------------------------------------
Future<bool> setCameraSelected(String value) async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.setString(_nameKey, value);
}
}

Answer 1

You can copy paste run full code below
Use SharedPreferences before runApp(MyApp());
and class CameraHomeScreen add a parameter for initCamera
and use it like this CameraHomeScreen(cameras, initCamera),
code snippet
String initCamera;
List<CameraDescription> cameras;
Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
cameras = await availableCameras();
SharedPreferences pre = await SharedPreferences.getInstance();
//await prefs.setString("cameraSelected","front");
initCamera = await pre.getString("cameraSelected");
print('initCamera ${initCamera}');
runApp(MyApp());
}
...
class CameraHomeScreen extends StatefulWidget {
List<CameraDescription> cameras;
String initCamera;
CameraHomeScreen(this.cameras, this.initCamera);
...
void initState() {
print( 'widget.initCamera ${widget.initCamera}' );
if (widget.initCamera == 'back') {
onCameraSelected(widget.cameras[0]);
} else {
onCameraSelected(widget.cameras[1]);
}
super.initState();
}
demo
full code
import 'dart:async';
import 'dart:io';
import 'package:camera/camera.dart';
import 'package:path_provider/path_provider.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
String initCamera;
List<CameraDescription> cameras;
Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
cameras = await availableCameras();
SharedPreferences pre = await SharedPreferences.getInstance();
//await prefs.setString("cameraSelected","front");
initCamera = await pre.getString("cameraSelected");
print('initCamera ${initCamera}');
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: CameraHomeScreen(cameras, initCamera),
);
}
}
class CameraHomeScreen extends StatefulWidget {
List<CameraDescription> cameras;
String initCamera;
CameraHomeScreen(this.cameras, this.initCamera);
#override
State<StatefulWidget> createState() {
return _CameraHomeScreenState();
}
}
class _CameraHomeScreenState extends State<CameraHomeScreen> {
String imagePath;
bool _toggleCamera = false;
String _currentCamera = 'back';
CameraController controller;
#override
void initState() {
print( 'widget.initCamera ${widget.initCamera}' );
if (widget.initCamera == 'back') {
onCameraSelected(widget.cameras[0]);
} else {
onCameraSelected(widget.cameras[1]);
}
super.initState();
}
#override
void dispose() {
controller?.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
if (widget.cameras.isEmpty) {
return Container(
alignment: Alignment.center,
padding: EdgeInsets.all(16.0),
child: Text(
'No Camera Found',
style: TextStyle(
fontSize: 16.0,
color: Colors.white,
),
),
);
}
if (!controller.value.isInitialized) {
return Container();
}
return AspectRatio(
aspectRatio: controller.value.aspectRatio,
child: Container(
child: Stack(
children: <Widget>[
CameraPreview(controller),
Align(
alignment: Alignment.bottomCenter,
child: Container(
width: double.infinity,
height: 120.0,
padding: EdgeInsets.all(20.0),
color: Color.fromRGBO(00, 00, 00, 0.7),
child: Stack(
children: <Widget>[
Align(
alignment: Alignment.center,
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(Radius.circular(50.0)),
onTap: () {
_captureImage();
},
child: Container(
padding: EdgeInsets.all(4.0),
child: Image.asset(
'assets/images/ic_shutter_1.png',
width: 72.0,
height: 72.0,
),
),
),
),
),
Align(
alignment: Alignment.centerRight,
child: Material(
color: Colors.transparent,
child: InkWell(
borderRadius: BorderRadius.all(Radius.circular(50.0)),
onTap: () {
if (!_toggleCamera) {
SharedPreferencesHelper prefs =
SharedPreferencesHelper();
prefs.setCameraSelected('front');
print("front");
onCameraSelected(widget.cameras[1]);
setState(() {
_toggleCamera = true;
});
} else {
SharedPreferencesHelper prefs =
SharedPreferencesHelper();
prefs.setCameraSelected('back');
print("back");
onCameraSelected(widget.cameras[0]);
setState(() {
_toggleCamera = false;
});
}
},
child: Container(
padding: EdgeInsets.all(4.0),
child: Image.asset(
'assets/images/ic_switch_camera_3.png',
color: Colors.grey[200],
width: 42.0,
height: 42.0,
),
),
),
),
),
],
),
),
),
],
),
),
);
}
void onCameraSelected(CameraDescription cameraDescription) async {
if (controller != null) await controller.dispose();
controller = CameraController(cameraDescription, ResolutionPreset.medium);
controller.addListener(() {
if (mounted) setState(() {});
if (controller.value.hasError) {
showMessage('Camera Error: ${controller.value.errorDescription}');
}
});
try {
await controller.initialize();
} on CameraException catch (e) {
showException(e);
}
if (mounted) setState(() {});
}
String timestamp() => new DateTime.now().millisecondsSinceEpoch.toString();
void _captureImage() {
takePicture().then((String filePath) {
if (mounted) {
setState(() {
imagePath = filePath;
});
if (filePath != null) {
showMessage('Picture saved to $filePath');
setCameraResult();
}
}
});
}
void setCameraResult() {
Navigator.pop(context, imagePath);
}
Future<String> takePicture() async {
if (!controller.value.isInitialized) {
showMessage('Error: select a camera first.');
return null;
}
final Directory extDir = await getApplicationDocumentsDirectory();
final String dirPath = '${extDir.path}/FlutterDevs/Camera/Images';
await new Directory(dirPath).create(recursive: true);
final String filePath = '$dirPath/${timestamp()}.jpg';
if (controller.value.isTakingPicture) {
// A capture is already pending, do nothing.
return null;
}
try {
await controller.takePicture(filePath);
} on CameraException catch (e) {
showException(e);
return null;
}
return filePath;
}
void showException(CameraException e) {
logError(e.code, e.description);
showMessage('Error: ${e.code}\n${e.description}');
}
void showMessage(String message) {
print(message);
}
void logError(String code, String message) =>
print('Error: $code\nMessage: $message');
}
class SharedPreferencesHelper {
///
/// Instantiation of the SharedPreferences library
///
final String _nameKey = "cameraSelected";
/// ------------------------------------------------------------
/// Method that returns the user decision on sorting order
/// ------------------------------------------------------------
Future<String> getCameraSelected() async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.getString(_nameKey) ?? 'name';
}
/// ----------------------------------------------------------
/// Method that saves the user decision on sorting order
/// ----------------------------------------------------------
Future<bool> setCameraSelected(String value) async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
return prefs.setString(_nameKey, value);
}
}