flutter 调用摄像头，前后镜头切换

参考
直播开播前的镜头调试，单纯的显示摄像头的内容
添加插件

camera: ^0.9.7+1

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:camera/camera.dart';

List<CameraDescription> cameras;

Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
   cameras = await availableCameras();
   runApp(CameraApp());
 }
 
 class CameraApp extends StatefulWidget {
   @override
   _CameraAppState createState() => _CameraAppState();
 }

 class _CameraAppState extends State<CameraApp> {
   CameraController controller;
 
  @override
  void initState() {
     super.initState();
     controller = CameraController(cameras[0], ResolutionPreset.medium);
     controller.initialize().then((_) {
       if (!mounted) {
         return;
       }
       setState(() {});
     });
   }
 
   @override
   void dispose() {
     controller?.dispose();
     super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
     if (!controller.value.isInitialized) {
       return Container();
     }
     return AspectRatio(
         aspectRatio:
         controller.value.aspectRatio,
         child: CameraPreview(controller));
   }
 }

我自己的代码，直播开播前的镜头调试，单纯的显示摄像头的内容

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:camera/camera.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:permission_handler/permission_handler.dart';

import '../../common/Global.dart';
import '../../common/backgroundWall.dart';
import '../../router.dart';

//开播页
class StartCameraSeeding extends StatefulWidget {
  @override
  StartCameraSeedingState createState() => StartCameraSeedingState();
}

class StartCameraSeedingState extends State<StartCameraSeeding> {
  CameraController? controller;
  late List<CameraDescription> cameras;
  //前后摄像头设置
  int frontCamera = 1;

  @override
  initState() {
    //请求权限
    if (Platform.isAndroid || Platform.isIOS) {
      Permission.camera.request().then((value) async {
        print('权限的值是多少${value}');
        await Permission.microphone.request().then((value) {} );
      });
    }
    super.initState();
    //初始化镜头
    initData().then((value) {});
  }

  initData() async {
    cameras = await availableCameras();
    controller = CameraController(cameras[frontCamera], ResolutionPreset.medium);
    if (controller != null) {
      controller!.initialize().then((_) {
        if (!mounted) {
          return;
        }
        mySetState(() {});
      });
    }
  }

  @override
  void dispose() {
    if (controller != null) {
      controller!.dispose();
    }

    super.dispose();
  }

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

  @override
  Widget build(BuildContext context) {
    if (controller == null) {
      return Container();
    } else if (controller != null) {
      if (!controller!.value.isInitialized) {
        return Container();
      }
    }
    return Material(
      child: Stack(
        alignment: Alignment.center,
        children: [
        //  AspectRatio(
           //   aspectRatio: Global.screenWidth/Global.screenHeight,
           //   child: CameraPreview(controller!)),
           //除以反转，就是正常的比例了，用Transform.scale放大填充满屏
                Center(
                child: Transform.scale(
                  scale: (1/controller!.value.aspectRatio)/deviceRatio,
                  child: AspectRatio(
                      aspectRatio: 1/controller!.value.aspectRatio,
                      child: CameraPreview(controller!)),
                ),
              ),
          Column(
            children: [
              addHeadView(),
              Container(
                margin: const EdgeInsets.only(left: 20, right: 20, top: 50),
                decoration: const BoxDecoration(color: Colors.transparent),
                child: Row(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    BackgroundWall(
                      width: 100,
                      height: 100,
                      hasPlaceholder: true,
                      radius: 4.r,
                      avatarUrl: 'assets/images/bg_none_nearby.png',
                      fit: BoxFit.cover,
                    ),
                    Container(
                      margin: const EdgeInsets.only(top: 15),
                      alignment: Alignment.topLeft,
                      child: Column(
                        children: const [
                          Text(
                            '请输入直播标题',
                            style: TextStyle(color: Colors.white, fontSize: 15),
                          )
                        ],
                      ),
                    )
                  ],
                ),
              ),
              Expanded(child: Container()),
              Row(
                children: [
                  Expanded(
                    child: GestureDetector(
                      onTap: (){
                        MyRouter.pushMyMap(context, MyRouter.directSeedingAnchor,
                            {"type":1});
                      },
                      child: Container(
                        margin: const EdgeInsets.only(left: 5, right: 5, bottom: 10),
                        padding: const EdgeInsets.only(top: 10, bottom: 10),
                        decoration: BoxDecoration(
                            color: Colors.red, borderRadius: BorderRadius.circular(20)),
                        child: Container(
                          alignment: Alignment.center,
                          child: const Text(
                            '开启视频直播',
                            style: TextStyle(color: Colors.white, fontSize: 16),
                          ),
                        ),
                      ),
                    ),
                  ),
                  GestureDetector(
                    onTap: (){
                      //前后镜头切换
                      if(frontCamera==1){
                        controller = CameraController(cameras[0], ResolutionPreset.medium);
                        if (controller != null) {
                          controller!.initialize().then((_) {
                            if (!mounted) {
                              return;
                            }
                            frontCamera=0;
                            mySetState((){});
                          });
                        }
                      }else{
                        controller = CameraController(cameras[1], ResolutionPreset.medium);
                        if (controller != null) {
                          controller!.initialize().then((_) {
                            if (!mounted) {
                              return;
                            }
                            frontCamera=1;
                            mySetState((){});
                          });
                        }
                      }
                    },
                    child: Container(
                      margin: const EdgeInsets.only(left: 5, right: 10, bottom: 10),
                      padding: const EdgeInsets.only(top: 10, bottom: 10),
                      child: const Image(
                        image: AssetImage('assets/images/bg_none_nearby.png'),
                        width: 35,
                        height: 35,
                      ),
                    ),
                  )
                ],
              )
            ],
          ),
        ],
      ),
    );
  }

  Widget addHeadView() {
    return Container(
        padding: EdgeInsets.only(top: Global.topHeight + 11.r, bottom: 20.r),
        child: Row(children: [
          GestureDetector(
            onTap: () {
              Navigator.pop(context);
            },
            child: Container(
              margin: EdgeInsets.only(left: 15.r, right: 12.r),
              child: const Image(
                image: AssetImage('assets/images/icon_back@2x.png'),
                width: 24,
                height: 24,
                color: Colors.white,
              ),
            ),
          ),
        ]));
  }
}