barcode_scanner_picklist.dart
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import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:mobile_scanner/mobile_scanner.dart';
import 'package:mobile_scanner_example/picklist/classes/barcode_at_center.dart';
import 'package:mobile_scanner_example/picklist/widgets/crosshair.dart';
import 'package:mobile_scanner_example/scanner_error_widget.dart';
// This sample implements picklist functionality.
// The scanning can temporarily be suspended by the user by touching the screen.
// When the scanning is active, the crosshair turns red.
// When the scanning is suspended, the crosshair turns green.
// A barcode has to touch the center of viewfinder to be scanned.
// Therefore the Crosshair widget needs to be placed at the center of the
// MobileScanner widget to visually line up.
class BarcodeScannerPicklist extends StatefulWidget {
const BarcodeScannerPicklist({super.key});
@override
State<BarcodeScannerPicklist> createState() => _BarcodeScannerPicklistState();
}
class _BarcodeScannerPicklistState extends State<BarcodeScannerPicklist> {
final _mobileScannerController = MobileScannerController(
// The controller is started from the initState method.
autoStart: false,
);
final orientation = DeviceOrientation.portraitUp;
// On this subscription the barcodes are received.
StreamSubscription<Object?>? _subscription;
// This boolean indicates if the detection of barcodes is enabled or
// temporarily suspended.
final _scannerEnabled = ValueNotifier(true);
// This boolean is used to prevent multiple pops.
var _validBarcodeFound = false;
@override
void initState() {
// Lock to portrait (may not work on iPad with multitasking).
SystemChrome.setPreferredOrientations([orientation]);
// Get a stream subscription and listen to received barcodes.
_subscription = _mobileScannerController.barcodes.listen(_handleBarcodes);
super.initState();
// Start the controller to start scanning.
unawaited(_mobileScannerController.start());
}
@override
void dispose() {
// Cancel the stream subscription.
unawaited(_subscription?.cancel());
_subscription = null;
super.dispose();
// Dispose the controller.
_mobileScannerController.dispose();
}
// Check the list of barcodes only if scannerEnables is true.
// Only take the barcode that is at the center of the image.
// Return the barcode found to the calling page with the help of the
// navigator.
void _handleBarcodes(BarcodeCapture barcodeCapture) {
// Discard all events when the scanner is disabled or when already a valid
// barcode is found.
if (!_scannerEnabled.value || _validBarcodeFound) {
return;
}
final barcode = findBarcodeAtCenter(barcodeCapture, orientation);
if (barcode != null) {
_validBarcodeFound = true;
Navigator.of(context).pop(barcode);
}
}
@override
Widget build(BuildContext context) {
return PopScope(
onPopInvoked: (didPop) {
// Reset the page orientation to the system default values, when this page is popped
if (!didPop) {
return;
}
SystemChrome.setPreferredOrientations(<DeviceOrientation>[]);
},
child: Scaffold(
appBar: AppBar(title: const Text('Picklist scanner')),
backgroundColor: Colors.black,
body: Listener(
// Detect if the user touches the screen and disable/enable the scanner accordingly
behavior: HitTestBehavior.opaque,
onPointerDown: (_) => _scannerEnabled.value = false,
onPointerUp: (_) => _scannerEnabled.value = true,
onPointerCancel: (_) => _scannerEnabled.value = true,
// A stack containing the image feed and the crosshair
// The location of the crosshair must be at the center of the MobileScanner, otherwise the detection area and the visual representation do not line up.
child: Stack(
fit: StackFit.expand,
children: [
MobileScanner(
controller: _mobileScannerController,
errorBuilder: (context, error, child) =>
ScannerErrorWidget(error: error),
fit: BoxFit.contain,
),
Crosshair(_scannerEnabled),
],
),
),
),
);
}
}