Flutter 相机错误 LateInitializationError: Field 'cameraController' has not been initialized

Question

我正在尝试编写代码以将相机与 Flutter 一起使用，但即使按照在线看到的步骤进行操作，它也无法初始化cameraController 。

这是我的代码：

class CameraPage extends StatefulWidget {
  const CameraPage({Key? key}) : super(key: key);

  @override
  State<CameraPage> createState() => _CameraPageState();
}

class _CameraPageState extends State<CameraPage> {

  late List<CameraDescription> cameras;
  late CameraController cameraController;

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

  void startCamera() async {
    cameras = await availableCameras();

    cameraController = CameraController(
        cameras[0],
        ResolutionPreset.high
    );

    print(" Camera controller : $cameraController");

    cameraController.initialize().then((value) {
      if(!mounted) {
        return;
      }
      setState(() {}); //To refresh widget

    }).catchError((e) {
      print(e);
    });
  }



  @override
  void dispose() {
    cameraController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {

    if(cameraController.value.isInitialized) {
      return Scaffold(
        body: Stack(
          children: [
            CameraPreview(cameraController),
          ],
        ),
      );
    } else {
      return SizedBox();
    }
  }
}

print(" Camera controller: $cameraController"); 工作正常并返回给我一个相机 controller，所以它可能会在某个时候初始化？

Answer 1

您的问题是，在第一次构建时，您的相机 controller 尚未初始化，因为初始化是在异步方法中进行的。 在访问 late 属性之前，您可以使用 Boolean 标志来跟踪初始化。

bool _cameraInitialized = false;

void startCamera() async {
    cameras = await availableCameras();

    cameraController = CameraController(cameras[0], ResolutionPreset.high);

    print(" Camera controller : $cameraController");

    cameraController.initialize().then((value) {
      if (!mounted) {
        return;
      }
      setState(() {
        _cameraInitialized = true; // updating the flag after camera is initialized
      }); //To refresh widget
    }).catchError((e) {
      print(e);
    });
  }

@override
  Widget build(BuildContext context) {
    if (_cameraInitialized && cameraController.value.isInitialized) {
      return Scaffold(
        body: Stack(
          children: [
            CameraPreview(cameraController),
          ],
        ),
      );
    } else {
      return SizedBox();
    }
  }

Answer 2

我会建议使用 FutureBuilder 来处理未来的方法。

class _CameraPageState extends State<CameraPage> {
  late List<CameraDescription> cameras;
  late CameraController cameraController;

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

  Future<void> startCamera() async {
    cameras = await availableCameras();
    cameraController = CameraController(cameras[0], ResolutionPreset.high);
  }

  late final cameraInit = Future.wait([
    startCamera(),
    cameraController.initialize(),
  ]);
  @override
  void dispose() {
    cameraController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          FutureBuilder(
            future: cameraInit,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                return CameraPreview(cameraController);
              } else {
                return const Center(child: CircularProgressIndicator());
              }
            },
          ),
        ],
      ),
    );
  }
}

还要检查这 本食谱。