[BUG] When open scan page then first time it is asking for the permission if user said "yes" then it is opening the camera but if user comes second time then it is displaying black page

[sahiram036]

Describe the bug I'm implementing a in-app QR scanner, Its only working once and then camera is not opening and I got a black screen.. and some logs listed below...

Flutter information ════════ Exception caught by widgets library ═══════════════════════════════════ The following assertion was thrown building FutureBuilder(dirty, state: _FutureBuilderState#50d2d): Failed assertion: boolean expression must not be null

The relevant error-causing widget was FutureBuilder lib\…\dine_in\qr_scan.dart:114 When the exception was thrown, this was the stack#0 _QRScanScrenState.build.lib\…\dine_in\qr_scan.dart:119

1 _FutureBuilderState.buildpackage:flutter/…/widgets/async.dart:615

2 StatefulElement.buildpackage:flutter/…/widgets/framework.dart:4919

3 ComponentElement.performRebuildpackage:flutter/…/widgets/framework.dart:4806

4 StatefulElement.performRebuildpackage:flutter/…/widgets/framework.dart:4977

5 Element.rebuildpackage:flutter/…/widgets/framework.dart:4529

6 ComponentElement._firstBuildpackage:flutter/…/widgets/framework.dart:4787

(elided 3 frames from dart:async) ════════ Exception caught by widgets library ═══════════════════════════════════ Failed assertion: boolean expression must not be null The relevant error-causing widget was FutureBuilder lib\…\dine_in\qr_scan.dart:114 ════════════════════════════════════════════════════════════════════════════════ [log] 2022-12-22T12:59:25.617752_onPermissionSet true

Additional context `import 'dart:convert'; import 'dart:developer';
import 'package:flutter/material.dart'; import 'package:qr_code_scanner/qr_code_scanner.dart'; import 'package:toast/toast.dart'; import 'package:app/custom/box_decorations.dart'; import 'package:app/custom/toast_component.dart'; import 'package:app/my_theme.dart'; import 'package:app/screens/new_query_screen.dart';

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

@override State createState() => _QRCodeScrenState(); }

class _QRCodeScrenState extends State { Barcode result; var resultCode = [];

QRViewController controller; final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');

@override void reassemble() { super.reassemble(); // if (Platform.isAndroid) { // controller.resumeCamera(); // } controller.pauseCamera(); controller.resumeCamera(); }

onPressContinue() async { ...............// CODE }

@override Widget build(BuildContext context) { return Scaffold( body: Column( children: [ Expanded( flex: 5, child: _buildQrView( context, ), ), Expanded( flex: 1, child: Padding( padding: const EdgeInsets.all(8), child: Row( mainAxisAlignment: MainAxisAlignment.spaceBetween, children: [ Row( mainAxisAlignment: MainAxisAlignment.spaceBetween, children: [ if (result != null) Container( width: 220, padding: EdgeInsets.only(right: 10), child: Column( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.center, children: [ Text( resultCode.toString(), style: TextStyle( fontSize: 14, color: MyTheme.accent_color, fontWeight: FontWeight.w500, ), ), SizedBox( height: 16, ), ], ), ) else Container( width: 200, child: Center( child: Row( children: [ Text( 'Scan QR Code', ), ], ), ), ), Column( mainAxisAlignment: MainAxisAlignment.end, crossAxisAlignment: CrossAxisAlignment.end, children: [ Row( children: [ FloatingActionButton.small( onPressed: () async { await controller?.toggleFlash(); setState(() {}); }, child: FutureBuilder( future: controller?.getFlashStatus(), builder: (context, snapshot) { // return Text('Flash: ${snapshot.data}'); return Icon( snapshot.data ? Icons.flashlight_off_sharp : Icons.flashlight_on_sharp, ); }, ), ), SizedBox( width: 26, ), FloatingActionButton.small( onPressed: () async { if (result != null) { Navigator.pop(context); } else { await controller?.resumeCamera(); } }, child: FutureBuilder( future: controller?.getFlashStatus(), builder: (context, snapshot) { // return Text('Flash: ${snapshot.data}'); return Icon( result != null ? Icons.close : Icons.qr_code, ); }, ), ), ], ), SizedBox( height: 10, ), if (result != null) Container( height: 30, width: 120, decoration: BoxDecorations.buildBoxDecoration_1(), child: FlatButton( padding: EdgeInsets.zero, color: MyTheme.amber, shape: RoundedRectangleBorder( borderRadius: BorderRadius.circular(6), side: BorderSide( color: MyTheme.golden, ), ), onPressed: () { onPressContinue(); }, child: Text( "Continue", style: TextStyle( fontSize: 12, color: MyTheme.golden, fontWeight: FontWeight.w700, ), ), ), ), ], ), ], ) ], ), ), ) ], ), ); }

Widget _buildQrView(BuildContext context) { // For this example we check how width or tall the device is and change the scanArea and overlay accordingly. var scanArea = (MediaQuery.of(context).size.width < 400 || MediaQuery.of(context).size.height < 400) ? 250.0 : 400.0; // To ensure the Scanner view is properly sizes after rotation // we need to listen for Flutter SizeChanged notification and update controller return QRView( key: qrKey, onQRViewCreated: _onQRViewCreated, overlay: QrScannerOverlayShape( borderColor: Colors.red, borderRadius: 10, borderLength: 30, borderWidth: 10, cutOutSize: scanArea), onPermissionSet: (ctrl, p) => _onPermissionSet(context, ctrl, p), ); }

void _onQRViewCreated(QRViewController controller) { setState( () { this.controller = controller; }, ); controller.scannedDataStream.listen( (scanData) async { try { result = scanData; resultCode = result.code.toString().split(",");

      setState(() {});
    } catch (e) {
      print("object-----------ERROR-------->$e");
    }
  },
);

}

void _onPermissionSet(BuildContext context, QRViewController ctrl, bool p) { log('${DateTime.now().toIso8601String()}_onPermissionSet $p'); if (!p) { ScaffoldMessenger.of(context).showSnackBar( const SnackBar( content: Text( 'No Permission', ), ), ); } }

@override void dispose() { controller.dispose(); super.dispose(); } }

`

[nr-ghost]

+1

[yazeed-mohammad]

see this comment, its helped me alhamdullah ..

  void _onQRViewCreated(QRViewController controller) {
    this.controller = controller;
    controller.resumeCamera();  //<--- add this line.
    controller.scannedDataStream.listen((scanData) {
      setState(() {
        result = scanData;
      });
    });
  }

[sahiram036]

see this comment, its helped me alhamdullah ..

  void _onQRViewCreated(QRViewController controller) {
    this.controller = controller;
    controller.resumeCamera();  //<--- add this line.
    controller.scannedDataStream.listen((scanData) {
      setState(() {
        result = scanData;
      });
    });
  }

Thank you working like charm !!

[sahiram036]

`void _onQRViewCreated(QRViewController controller) { setState(() { this.controller = controller; resuecamara(); }); controller.scannedDataStream.listen((scanData) { setState(() { result = scanData; print(result!.code); }); }); }

void resuecamara() { if (Platform.isAndroid) { controller!.pauseCamera(); } controller!.resumeCamera(); }`