Stop the Scan, Not the Camera: Implementing Continuous QR Code Scanning in Flutter
QR code scanning has become ubiquitous in our daily lives, offering a seamless way to access information and perform actions. In Flutter, the qr_code_scanner package provides a simple and effective way to integrate this functionality. However, a common challenge arises when you want the camera to continuously scan for QR codes after a successful scan, without requiring the user to manually restart the process.
This article explores how to achieve this continuous scanning behavior, allowing your Flutter app to automatically detect and process QR codes without interruption.
The Challenge: A Single Scan and Done
The qr_code_scanner package's default behavior is to stop scanning once a QR code is detected. This can be frustrating for users who need to scan multiple codes in a short period. Imagine a scenario where a user needs to scan multiple items in a store. After each scan, they would have to manually tap the "scan again" button, hindering the flow and efficiency.
Original Code (Simplified):
import 'package:flutter/material.dart';
import 'package:qr_code_scanner/qr_code_scanner.dart';
class QRScannerPage extends StatefulWidget {
@override
_QRScannerPageState createState() => _QRScannerPageState();
}
class _QRScannerPageState extends State<QRScannerPage> {
final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
QRViewController? controller;
@override
void dispose() {
controller?.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('QR Code Scanner')),
body: QRView(
key: qrKey,
onQRViewCreated: _onQRViewCreated,
),
);
}
void _onQRViewCreated(QRViewController controller) {
this.controller = controller;
controller.scannedDataStream.listen((scanData) {
// Process the scanned data
// The scanner stops after this line
});
}
}
Explanation:
This code demonstrates a basic QR code scanner in Flutter. After the QR code is scanned, the scannedDataStream.listen function processes the data and then stops scanning. We need to modify this behavior to achieve continuous scanning.
The Solution: Restarting the Scan Loop
The key to continuous scanning is to restart the scan process after each successful QR code detection. This can be achieved by using a timer or a loop to trigger the scan again after a brief delay.
Modified Code:
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:qr_code_scanner/qr_code_scanner.dart';
class QRScannerPage extends StatefulWidget {
@override
_QRScannerPageState createState() => _QRScannerPageState();
}
class _QRScannerPageState extends State<QRScannerPage> {
final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
QRViewController? controller;
Timer? _timer;
@override
void dispose() {
_timer?.cancel();
controller?.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('QR Code Scanner')),
body: QRView(
key: qrKey,
onQRViewCreated: _onQRViewCreated,
),
);
}
void _onQRViewCreated(QRViewController controller) {
this.controller = controller;
controller.scannedDataStream.listen((scanData) {
// Process the scanned data
_restartScan();
});
}
void _restartScan() {
_timer?.cancel();
_timer = Timer(Duration(milliseconds: 500), () {
controller?.resumeCamera();
});
}
}
Explanation:
- We introduce a
Timer(_timer) to handle the delay between scans. - The
_restartScan()function is called after each successful scan. _restartScan()cancels the previous timer and starts a new one with a 500ms delay.- After the delay,
controller?.resumeCamera()is called to restart the scan process.
This implementation ensures that the QR code scanner continues to scan for new codes even after a successful detection, providing a seamless and efficient user experience.
Enhancements and Considerations
- Scan Interval: Adjust the delay in
_restartScan()to control the scanning frequency. A shorter delay will increase the scan rate, while a longer delay will reduce the scan frequency. - User Feedback: Consider providing visual feedback to the user, such as a blinking indicator or a message, to inform them that the scanner is still active and waiting for another code.
- Error Handling: Implement error handling mechanisms to deal with potential issues such as camera permission errors or connection problems.
- Performance Optimization: For scenarios where the scanning frequency is high, consider optimizing the scan process to avoid unnecessary resource consumption.
Conclusion
By incorporating a simple timer mechanism, you can transform your Flutter QR code scanner into a continuous scanning powerhouse. This enhanced functionality empowers your app to seamlessly handle multiple QR codes, boosting efficiency and improving the user experience. Remember to adjust the delay and consider adding visual feedback to provide a smooth and intuitive experience for your users.
