A simple flutter camera that capture photos and display them. Thanks to https://flutter.dev/docs/ docs

Camera.dart

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

void main() async {
    // Making sure that the plugin services are initialized so that `availableCameras()`
    // can be called before `runApp()`
    WidgetsFlutterBinding.ensureInitialized();

    // Now lets get all the available cameras
    final cameras = await availableCameras();
    // finally let's use the back camera.
    final firstCamera = cameras.first;

    runApp(CameraApp(camera:firstCamera));
}

// A screen that allows users to take a picture using a given camera.
class CameraApp extends StatefulWidget {
  final CameraDescription camera;

  const CameraApp({ Key key,@required this.camera }) : super(key: key);

  @override
  TakePictureScreenState createState() => TakePictureScreenState();
}

class TakePictureScreenState extends State<CameraApp> {
  CameraController _controller;
  Future<void> _initializeControllerFuture;

  @override
  void initState() {
    super.initState();
    // To display the current output from the Camera,
    // create a CameraController.
    _controller = CameraController(
      // Get a specific camera from the list of available cameras i.e back,front
      widget.camera,
      // Define the resolution to use.
      ResolutionPreset.medium,
    );

    // Next, initialize the controller. This returns a Future.
    _initializeControllerFuture = _controller.initialize();
  }

  @override
  void dispose() {
    // Dispose of the controller when the widget is disposed.
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // You must wait until the controller is initialized before displaying the
      // camera preview. Use a FutureBuilder to display a loading spinner until the
      // controller has finished initializing.
      body: FutureBuilder<void>(
        future: _initializeControllerFuture,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            // If the Future is complete, display the preview.
            return CameraPreview(_controller);
          } else {
            // Otherwise, display a loading indicator.
            return const Center(child: CircularProgressIndicator());
          }
        },
      ),
      bottomNavigationBar: bottomNavigationBar(),
    );
  }
   // We put all the camera controls here 
  // like the capture button. You can add your custom one 
  // like flash or toggle camera mode and code its functionality
  Widget bottomNavigationBar(){
    return Container(
      color: Colors.black,
      height: 140,
      width: MediaQuery.of(context).size.width,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          SizedBox(width: 45,),
          Container(
              child: Align(
                alignment: Alignment.center,
                child:Material(
                    color: Colors.black,
                    child : InkResponse(
                      child: Container(
                        width: 80,
                        height: 80,
                        decoration: BoxDecoration(
                          borderRadius: BorderRadius.all(Radius.circular(60)),
                          border: Border.all(
                            width: 3,
                            color: Colors.white,
                            style: BorderStyle.solid,
                          ),
                        ),
                      ),
                      highlightColor: Colors.blueAccent,
                      onTap: (){ captureImage(); },
                    )
                ),
              )
          ),
          SizedBox(width: 45,)
        ],
      ),
    );
  }

  void captureImage() async {
    // Take the Picture in a try / catch block. If anything goes wrong,
    // catch the error.
    try {
      // Ensure that the camera is initialized.
      await _initializeControllerFuture;

      // Attempt to take a picture and get the file `image`
      // where it was saved.
      final image = await _controller.takePicture();

      // If the picture was taken, display it on a new screen.
      await Navigator.of(context).push(
        MaterialPageRoute( builder: (context) => DisplayImage( imagePath: image.path));

    } catch (e) {
      // If an error occurs, log the error to the console.
      print(e);
    }
  }
}

class DisplayImage extends StatelessWidget {
    final String imagePath;
    const DisplayImage({Key key, @required this.imagePath}) : super(key: key);
    String fileName = this.imagePath.split('/').last;
    @override
    Widget build(BuildContext context) {
        return Scaffold(
            appBar: AppBar(title: const Text(fileName)),
            body: Image.file(File(imagePath)),
        );
    }
}