flutter ページ遷移先のカメラがうまく作動しない

前提・実現したいこと

flutterで、ページの遷移先にカメラを起動させようとしているのですが、カメラが起動していません。みなさまのお知恵をお貸しいただけないでしょうか。カメラのソースコードは、flutter 公式HPのcookbookを参考にしました。
リンク先: https://flutter.dev/docs/cookbook/plugins/picture-using-camera

発生している問題・エラーメッセージ

ページ先のカメラが起動しません。カメラの情報が、ページの遷移先にうまく渡せていないのかもしれません。
エラーメッセージはないのですが、main.dart の下から7行目のTakePictureScreen()のところに「The 'camera' parameter is required.」と警告がでてしまいます。また、main.dartの上から12行目(空白入れて)のcameraFirstにも、「The value of the local variable 'firstCamera' isn't used.」と警告でてしまっています

・The parameter 'camera' is required.
・The value of the local variable 'firstCamera' isn't used.
Try removing the variable, or using it.

該当のソースコード

main.dart

dart
1import 'camera.dart';
2import 'package:flutter/material.dart';
3import 'package:camera/camera.dart';
4
5
6List<CameraDescription> cameras;
7Future<void> main() async{
8  WidgetsFlutterBinding.ensureInitialized();
9
10
11  final cameras = await availableCameras();
12  final firstCamera = cameras.first;
13  runApp(MyApp());
14
15
16
17}
18
19class MyApp extends StatelessWidget {
20  @override
21  Widget build (BuildContext context){
22    return MaterialApp(
23        title: 'Sort cam',
24        theme: ThemeData(
25          primarySwatch:Colors.blue,
26        ),
27        home: MyHomePage()
28    );
29  }
30}
31class MyHomePage extends StatelessWidget{
32  @override
33  Widget build(BuildContext context){
34    return Scaffold(
35      appBar:AppBar(
36          title: const Text('sort cam'),
37          actions: <Widget>[
38            IconButton(icon: Icon(Icons.settings),
39            onPressed:(){},
40          )
41          ]
42      ),
43      body: Center(
44        child: RaisedButton(onPressed: () {
45          Navigator.push(
46            context,
47            MaterialPageRoute(
48              builder: (contest) => TakePictureScreen()),
49          );  
50        }, child: Text('カメラを起動'))
51      ),
52    );
53  }
54}

camera.dart

dart
1import 'dart:io';
2import 'package:camera/camera.dart';
3import 'package:flutter/cupertino.dart';
4import 'package:flutter/material.dart';
5import 'dart:async';
6
7
8class TakePictureScreen extends StatefulWidget {
9  
10  final CameraDescription camera;
11
12  const TakePictureScreen({
13    Key key,
14    @required this.camera,
15  }) : super(key: key);
16
17  @override
18  TakePictureScreenState createState() => TakePictureScreenState();
19}
20
21class TakePictureScreenState extends State<TakePictureScreen> {
22  CameraController _controller;
23  Future<void> _initializeControllerFuture;
24
25  @override
26  void initState() {
27    super.initState();
28    // To display the current output from the Camera,
29    // create a CameraController.
30    _controller = CameraController(
31      // Get a specific camera from the list of available cameras.
32      widget.camera,
33      // Define the resolution to use.
34      ResolutionPreset.medium,
35    );
36
37    // Next, initialize the controller. This returns a Future.
38    _initializeControllerFuture = _controller.initialize();
39  }
40
41  @override
42  void dispose() {
43    // Dispose of the controller when the widget is disposed.
44    _controller.dispose();
45    super.dispose();
46  }
47
48  @override
49  Widget build(BuildContext context) {
50    return Scaffold(
51      appBar: AppBar(title: Text('Take a picture')),
52      // Wait until the controller is initialized before displaying the
53      // camera preview. Use a FutureBuilder to display a loading spinner
54      // until the controller has finished initializing.
55      body: FutureBuilder<void>(
56        future: _initializeControllerFuture,
57        builder: (context, snapshot) {
58          if (snapshot.connectionState == ConnectionState.done) {
59            // If the Future is complete, display the preview.
60            return CameraPreview(_controller);
61          } else {
62            // Otherwise, display a loading indicator.
63            return Center(child: CircularProgressIndicator());
64          }
65        },
66      ),
67      floatingActionButton: FloatingActionButton(
68        child: Icon(Icons.camera_alt),
69        // Provide an onPressed callback.
70        onPressed: () async {
71          // Take the Picture in a try / catch block. If anything goes wrong,
72          // catch the error.
73          try {
74            // Ensure that the camera is initialized.
75            await _initializeControllerFuture;
76
77            // Attempt to take a picture and get the file `image`
78            // where it was saved.
79            final image = await _controller.takePicture();
80
81            // If the picture was taken, display it on a new screen.
82            Navigator.push(
83              context,
84              MaterialPageRoute(
85                builder: (context) => DisplayPictureScreen(
86                  // Pass the automatically generated path to
87                  // the DisplayPictureScreen widget.
88                  imagePath: image?.path,
89                ),
90              ),
91            );
92          } catch (e) {
93            // If an error occurs, log the error to the console.
94            print(e);
95          }
96        },
97      ),
98    );
99  }
100}
101
102// A widget that displays the picture taken by the user.
103class DisplayPictureScreen extends StatelessWidget {
104  final String imagePath;
105
106  const DisplayPictureScreen({Key key, this.imagePath}) : super(key: key);
107
108  @override
109  Widget build(BuildContext context) {
110    return Scaffold(
111      appBar: AppBar(title: Text('Display the Picture')),
112      // The image is stored as a file on the device. Use the `Image.file`
113      // constructor with the given path to display the image.
114      body: Image.file(File(imagePath)),
115    );
116  }
117}
118

試したこと

main.dart の下から7行目のTakePictureScreen()の中に、camera: firstCameraと入れてみたのですが、「Undefinedname 'firstCamera'」とでてしまいます。(main.dartの、空白入れて上から12行目に宣言しているのにもかかわらず)

補足情報（FW/ツールのバージョンなど）

pubspec.yamlのdependenciesは、
camera: ^0.7.0+2　です。
android > app> build.gradle のminSDKversionは23にしました。
どなたかご回答お願いいたします。

行動規範の内容に同意します

回答1件

ベストアンサー

final firstCamera = cameras.first;
は、main() {}の中でのみ有効になっているので、引数として渡していく必要があるかと思います。

dart
1List<CameraDescription> cameras;
2
3Future<void> main() async{
4  WidgetsFlutterBinding.ensureInitialized();
5  final cameras = await availableCameras();
6  final firstCamera = cameras.first;
7  runApp(MyApp(camera: firstCamera,));
8}
9
10class MyApp extends StatelessWidget {
11  final CameraDescription camera;
12  const MyApp({Key key, @required this.camera}) : super(key: key);
13
14  @override
15  Widget build (BuildContext context){
16    return MaterialApp(
17        title: 'Sort cam',
18        theme: ThemeData(
19          primarySwatch:Colors.blue,
20        ),
21        home: MyHomePage(camera: camera)
22    );
23  }
24}
25
26class MyHomePage extends StatelessWidget{
27  final CameraDescription camera;
28  const MyHomePage({Key key, @required this.camera}) : super(key: key);
29
30  @override
31  Widget build(BuildContext context){
32    return Scaffold(
33      appBar:AppBar(
34          title: const Text('sort cam'),
35          actions: <Widget>[
36            IconButton(icon: Icon(Icons.settings),
37              onPressed:(){},
38            )
39          ]
40      ),
41      body: Center(
42          child: RaisedButton(onPressed: () {
43            // Navigator.push(
44            //   context,
45            //   MaterialPageRoute(
46            //       builder: (contest) => TakePictureScreen()),
47            // );
48            Navigator.push(context, MaterialPageRoute(builder: (context) => TakePictureScreen(camera: camera)));
49          }, child: Text('カメラを起動'))
50      ),
51    );
52  }
53}