获取可用的摄像机并在initState（）中使用其中一个摄像机初始化摄像机控制器。另外，将可用的相机存储到类变量中。

CameraController _controller;
 List<CameraDescription> _availableCameras;

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

 // get available cameras
 Future<void> _getAvailableCameras() async{
   WidgetsFlutterBinding.ensureInitialized();
   _availableCameras = await availableCameras();
   _initCamera(_availableCameras.first);
 }

 // init camera
 Future<void> _initCamera(CameraDescription description) async{
  _controller = CameraController(description, ResolutionPreset.max, enableAudio: true);

  try{
    await _controller.initialize();
    // to notify the widgets that camera has been initialized and now camera preview can be done
    setState((){}); 
  }
  catch(e){
    print(e);
  }  
}

只需重新初始化相机控制器与一个新的相机描述按钮点击。

void _toggleCameraLens() {
 // get current lens direction (front / rear)
 final lensDirection =  _controller.description.lensDirection;
 CameraDescription newDescription;
 if(lensDirection == CameraLensDirection.front){
    newDescription = _availableCameras.firstWhere((description) => description.lensDirection == CameraLensDirection.back);
 }
 else{
    newDescription = _availableCameras.firstWhere((description) => description.lensDirection == CameraLensDirection.front);
 }

  if(newDescription != null){
    _initCamera(newDescription);
  }
  else{
    print('Asked camera not available');
  }

}

我有两个建议
1.请使用软件包camera_camera https://github.com/gabulsavul/camera_camera
它提供了一个很好的例子和很多功能。
您可以直接使用或修改此软件包。
此软件包的屏幕

1.官方示例代码
https://github.com/flutter/plugins/blob/master/packages/camera/example/lib/main.dart
通过此功能切换摄像头
你可以直接用这个例子

void onNewCameraSelected(CameraDescription cameraDescription) async {
if (controller != null) {
  await controller.dispose();
}
controller = CameraController(
  cameraDescription,
  ResolutionPreset.high,
  enableAudio: enableAudio,
);

// If the controller is updated then update the UI.
controller.addListener(() {
  if (mounted) setState(() {});
  if (controller.value.hasError) {
    showInSnackBar('Camera error ${controller.value.errorDescription}');
  }
});

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

if (mounted) {
  setState(() {});
}
}

显示一行切换以选择摄像机

Widget _cameraTogglesRowWidget() {
final List<Widget> toggles = <Widget>[];

if (cameras.isEmpty) {
  return const Text('No camera found');
} else {
  for (CameraDescription cameraDescription in cameras) {
    toggles.add(
      SizedBox(
        width: 90.0,
        child: RadioListTile<CameraDescription>(
          title: Icon(getCameraLensIcon(cameraDescription.lensDirection)),
          groupValue: controller?.description,
          value: cameraDescription,
          onChanged: controller != null && controller.value.isRecordingVideo
              ? null
              : onNewCameraSelected,
        ),
      ),
    );
  }
}

你可以这样做：

onTap: () {
      this.setState(() {
        /// Change the current selected camera State.
        this.selectedCamera =this.selectedCamera == 0 ? 1 : 0;
      });

      this._cameraController = CameraController(
          this._camerasAvailable[this.selectedCamera],
          ResolutionPreset.max,
      );
      /// Reinit camera.
      this.cameraInitialize = this._cameraController.initialize();
         
    }

这是我的解决方案：

List<CameraDescription> cameras = [];
  late CameraController _controller;
  Future<void>? _initializeControllerFuture;

...

  void _toggleCameraLens()
  {
    if (cameras.length <= 2) {
      return;
    }

    final lensDirection = _controller.description.lensDirection;
    if (lensDirection == CameraLensDirection.front)
    {
      setState(() {
        _controller = CameraController(
          cameras.first,
          ResolutionPreset.medium,
        );
      });
    }
    else
    {
      setState(() {
        _controller = CameraController(
          cameras.last,
          ResolutionPreset.medium,
        );
      });
    }

    _initializeControllerFuture = _controller.initialize();
  }