Question

我正在构建一个需要摄像头的应用程序，当我在我的设备上测试它时，一切都很好，直到我打开摄像头。

当我完成注册过程并从底部导航打开相机时，应用程序崩溃并收到错误消息：

Lost connection to device.

此错误没有其他详细信息，因此我很难找到问题的确切来源。有什么想法吗？

class CameraScreen extends StatefulWidget {
  @override
  _CameraScreenState createState() => _CameraScreenState();
}

class _CameraScreenState extends State {
  CameraController controller;
  List cameras;
  int selectedCameraIndex;
  String imgPath;

  @override
  void initState() {
    super.initState();
    availableCameras().then((availableCameras) {
      cameras = availableCameras;

      if (cameras.length > 0) {
        setState(() {
          selectedCameraIndex = 0;
        });
        _initCameraController(cameras[selectedCameraIndex]).then((void v) {});
      } else {
        print('No camera available');
      }
    }).catchError((err) {
      print('Error :${err.code}Error message : ${err.message}');
    });
  }

  Future _initCameraController(CameraDescription cameraDescription) async {
    if (controller != null) {
      await controller.dispose();
    }
    controller = CameraController(cameraDescription, ResolutionPreset.high);

    controller.addListener(() {
      if (mounted) {
        setState(() {});
      }

      if (controller.value.hasError) {
        print('Camera error ${controller.value.errorDescription}');
      }
    });

    try {
      await controller.initialize();
    } on CameraException catch (e) {
      _showCameraException(e);
    }
    if (mounted) {
      setState(() {});
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: SafeArea(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
              Expanded(
                flex: 1,
                child: _cameraPreviewWidget(),
              ),
              Align(
                alignment: Alignment.bottomCenter,
                child: Container(
                  height: 120,
                  width: double.infinity,
                  padding: EdgeInsets.all(15),
                  color: Colors.black,
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.start,
                    children: <Widget>[
                      _cameraToggleRowWidget(),
                      _cameraControlWidget(context),
                      Spacer()
                    ],
                  ),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }

  /// Display Camera preview.
  Widget _cameraPreviewWidget() {
    if (controller == null || !controller.value.isInitialized) {
      return const Text(
        'Loading',
        style: TextStyle(
          color: Colors.white,
          fontSize: 20.0,
          fontWeight: FontWeight.w900,
        ),
      );
    }

    return AspectRatio(
      aspectRatio: controller.value.aspectRatio,
      child: CameraPreview(controller),
    );
  }

  /// Display the control bar with buttons to take pictures
  Widget _cameraControlWidget(context) {
    return Expanded(
      child: Align(
        alignment: Alignment.center,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          mainAxisSize: MainAxisSize.max,
          children: <Widget>[
            FloatingActionButton(
              child: Icon(
                Icons.camera,
                color: Colors.black,
              ),
              backgroundColor: Colors.white,
              onPressed: () {
                _onCapturePressed(context);
              },
            )
          ],
        ),
      ),
    );
  }

  /// Display a row of toggle to select the camera (or a message if no camera is available).
  Widget _cameraToggleRowWidget() {
    if (cameras == null || cameras.isEmpty) {
      return Spacer();
    }
    CameraDescription selectedCamera = cameras[selectedCameraIndex];
    CameraLensDirection lensDirection = selectedCamera.lensDirection;

    return Expanded(
      child: Align(
        alignment: Alignment.centerLeft,
        child: FlatButton.icon(
          onPressed: _onSwitchCamera,
          icon: Icon(
            _getCameraLensIcon(lensDirection),
            color: Colors.white,
            size: 24,
          ),
          label: Text(
            '${lensDirection.toString().substring(lensDirection.toString().indexOf('.') + 1).toUpperCase()}',
            style: TextStyle(color: Colors.white, fontWeight: FontWeight.w500),
          ),
        ),
      ),
    );
  }

  IconData _getCameraLensIcon(CameraLensDirection direction) {
    switch (direction) {
      case CameraLensDirection.back:
        return CupertinoIcons.switch_camera;
      case CameraLensDirection.front:
        return CupertinoIcons.switch_camera_solid;
      case CameraLensDirection.external:
        return Icons.camera;
      default:
        return Icons.device_unknown;
    }
  }

  void _showCameraException(CameraException e) {
    String errorText = 'Error:${e.code}\nError message : ${e.description}';
    print(errorText);
  }

  void _onCapturePressed(context) async {
    try {
      final path =
          join((await getTemporaryDirectory()).path, '${DateTime.now()}.png');
      await controller.takePicture();

      Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) => PreviewScreen(
                  imgPath: path,
                )),
      );
    } catch (e) {
      _showCameraException(e);
    }
  }

  void _onSwitchCamera() {
    selectedCameraIndex =
        selectedCameraIndex < cameras.length - 1 ? selectedCameraIndex + 1 : 0;
    CameraDescription selectedCamera = cameras[selectedCameraIndex];
    _initCameraController(selectedCamera);
  }
}

Answer 1

请确保以下两点：

在安卓清单中添加 android:requestLegacyExternalStorage="true"
在 ios info.plist（位于 /ios/Runner/Info.plist）中以键（粗体）和字符串格式添加这些行

NSPhotoLibraryUsageDescription

此应用需要访问照片库。

NSMicrophoneUsageDescription

此应用不需要使用麦克风。

NSCameraUsageDescription

此应用需要访问相机。

与设备的连接丢失 |打开相机

1 个答案: