Use Flutter study notes 03-- common plug-ins

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Two-dimensional code and bar code scanning plug qrscan

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  qrscan: ^0.1.3

import 'package:flutter/material.dart';
import 'package:qrscan/qrscan.dart' as scanner;

void main() => runApp(MyApp());

class MyApp extends StatefulWidget{
  MyApp({Key key}) : super(key: key);

  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String barcode = "";

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
       home: Scaffold(
        appBar: AppBar(
          title: Text('Scan barcodes and qr codes'),
        ),  
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.end, 
            children: <Widget>[
              Text(barcode),
              MaterialButton(
                onPressed: scan,
                child: Text("Scan"),
                color: Colors.blue,
                textColor: Colors.white,
              ),
            ] 
          ),  
        ),
       ), 
    );
  }

  Future scan() async {
    try {
      String barcode = await scanner.scan();
      setState(() => this.barcode = barcode);
    } on Exception catch (e) {
      if (e == scanner.CameraAccessDenied) {
        setState(() {
          this.barcode = 'The user did not grant the camera permission!';
        });
      } else {
        setState(() => this.barcode = 'Unknown error: $e');
      }
    } on FormatException {
      setState(() => this.barcode = 'null (User returned using the "back"-button before scanning anything. Result)');
    } catch (e) {
     setState(() => this.barcode = 'Unknown error: $e');
    }
  }
}