A QR code generation library for Dart and Flutter.
- Supports QR code versions 1 - 40
- Error correction / redundancy
To start, import the dependency in your code:
import 'package:qr/qr.dart';To build your QR code data you should do so as such:
final qrCode = QrCode(4, QrErrorCorrectLevel.L)
..addData('Hello, world in QR form!');
final qrImage = QrImage(qrCode);Now you can use your qrImage instance to render a graphical representation of
the QR code. A basic implementation would be as such:
for (var x = 0; x < qrImage.moduleCount; x++) {
for (var y = 0; y < qrImage.moduleCount; y++) {
if (qrImage.isDark(y, x)) {
// render a dark square on the canvas
}
}
}See the example directory for further details.
import 'package:flutter/material.dart';
import 'package:qr/qr.dart';
class QrCodeGenWidget extends StatefulWidget {
final String data;
final double size;
const QrCodeGenWidget({
super.key,
required this.data,
required this.size,
});
@override
State<QrCodeGenWidget> createState() => _QrCodeGenWidgetState();
}
class _QrCodeGenWidgetState extends State<QrCodeGenWidget> {
late var _qrImage = QrImage(
QrCode.fromData(
data: widget.data,
errorCorrectLevel: QrErrorCorrectLevel.L,
),
);
@override
void didUpdateWidget(QrCodeGenWidget oldWidget) {
super.didUpdateWidget(oldWidget);
if (widget.data != oldWidget.data) {
_qrImage = QrImage(
QrCode.fromData(
data: widget.data,
errorCorrectLevel: QrErrorCorrectLevel.L,
),
);
}
}
@override
Widget build(BuildContext context) {
return CustomPaint(
size: Size.square(widget.size),
isComplex: false,
willChange: false,
painter: _QrPainter(qrImage: _qrImage),
);
}
}
class _QrPainter extends CustomPainter {
final QrImage qrImage;
_QrPainter({required this.qrImage});
@override
bool shouldRepaint(covariant _QrPainter oldDelegate) {
return oldDelegate.qrImage != qrImage;
}
@override
void paint(Canvas canvas, Size size) {
final paint = Paint()
..color = Colors.black
..isAntiAlias = false;
canvas.scale(size.height / qrImage.moduleCount);
for (var x = 0; x < qrImage.moduleCount; x++) {
for (var y = 0; y < qrImage.moduleCount; y++) {
if (qrImage.isDark(y, x)) {
canvas.drawRect(
Rect.fromLTWH(x.toDouble(), y.toDouble(), 1, 1),
paint,
);
}
}
}
}
}
The following libraries use qr.dart to generate QR codes for you out of the box:
qr_flutter - A Flutter Widget to render QR codes
barcode - A package that supports many types of scannable codes, include QR.
A working demo can be found here: kevmoo.github.io/qr.dart