StateError (Bad state: No element) on IOS only - ios

Question

This error does not occur on Android or web but only on IOS. It seem very trivial but I can't figure out what's wrong.
import 'dart:developer';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'dart:convert';
import 'package:qr_code_scanner/qr_code_scanner.dart';
class ScanQrPage extends StatefulWidget {
#override
_ScanQrPageState createState() => _ScanQrPageState();
}
class _ScanQrPageState extends State<ScanQrPage> {
final qrKey = GlobalKey();
late QRViewController qrViewController;
late Barcode barcode;
// In order to get hot reload to work we need to pause the camera if the platform
// is android, or resume the camera if the platform is iOS.
#override
void reassemble() {
super.reassemble();
if (Platform.isAndroid) {
qrViewController.pauseCamera();
} else if (Platform.isIOS) {
qrViewController.resumeCamera();
}
}
#override
Widget build(BuildContext context) {
return WillPopScope(
onWillPop: () {
Navigator.of(context).pop("");
return new Future(() => true);
},
child: Scaffold(
body: Stack(
children: [
buildQrView(context),
],
),
),
);
}
Widget buildQrView(BuildContext context) {
return QRView(
onQRViewCreated: onQRViewCreated,
key: qrKey,
overlay: QrScannerOverlayShape(
cutOutSize: MediaQuery.of(context).size.width * 0.8),
onPermissionSet: (ctrl, p) => _onPermissionSet(context, ctrl, p),
);
}
void _onPermissionSet(BuildContext context, QRViewController ctrl, bool p) {
log('${DateTime.now().toIso8601String()}_onPermissionSet $p');
if (!p) {
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(content: Text('no Permission')),
);
}
}
#override
void dispose() {
qrViewController.dispose();
super.dispose();
}
void onQRViewCreated(QRViewController qrViewController) {
setState(() {
this.qrViewController = qrViewController;
});
qrViewController.scannedDataStream.listen((event) {
setState(() {
this.barcode = event;
if (Platform.isAndroid) {
qrViewController.pauseCamera();
} else if (Platform.isIOS) {
qrViewController.resumeCamera();
}
String rawData = event.code;
Uri data = Uri.dataFromString(rawData);
String para1 = data.queryParameters["buy"] ??
""; //get parameter with attribute "para1"
Codec<String, String> stringToBase64 = utf8.fuse(base64);
if (para1 != "") {
placer = stringToBase64.decode(para1);
}
WidgetsBinding.instance?.addPostFrameCallback((timeStamp) {
Navigator.pop(context, placer);
});
});
});
}
}
I've tried all the solutions with the same error found on stackoverflow (addPostFrameCallback and Future(Duration.zero)) but none of them are exactly the same and does not seem to fix my problem.
I don't think I have having the same issue as any of the other questions.
The exception is happening on the Navigator.pop(context, placer);
Does anyone have any idea how to overcome this?
Why does this only happen on IOS?