Flutter: '_debugLifecycleState == _StateLifecycle.ready': is not true

Question

I am trying do develop a flutter mobile app that can read a qr code. But everytime I press the back button on the emulator it gives the error: '_debugLifecycleState == _StateLifecycle.ready': is not true.

Below is the code:

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

  @override
  State<QRScan> createState() => _QRScanState();
}

class _QRScanState extends State<QRScan> {
  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
  Barcode? result;
  QRViewController? controller;
  @override
  void reassemble() {
    super.reassemble();
    if (Platform.isAndroid) {
      controller!.pauseCamera();
    } else if (Platform.isIOS) {
      controller!.resumeCamera();
    }
  }
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        await controller?.stopCamera();
        super.dispose();
        return true;
      },
      child: Scaffold(
        body: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Container(
              margin: EdgeInsets.only(top: 60),
              child: Center(
                child: Text(
                  'Scan QR Code',
                  style: GoogleFonts.epilogue(
                      textStyle: TextStyle(
                        fontSize: 16,
                        fontWeight: FontWeight.w700,
                        color: cardcolor2,
                        fontStyle: FontStyle.normal,
                      )
                  ),
                ),
              ),
            ),
            Container(
              margin: EdgeInsets.only(top: 20, left: 50, right: 64),
              child: Center(
                child: Text(
                  'Scan QR Code on kiosk to directly call the customer support',
                  textAlign: TextAlign.center,
                  style: GoogleFonts.epilogue(
                      textStyle: TextStyle(
                        fontSize: 14,
                        fontWeight: FontWeight.w500,
                        color: Colors.black,
                        fontStyle: FontStyle.normal,
                      )
                  ),
                ),
              ),
            ),
            Container(
              margin: EdgeInsets.only(top: 27),
              color: Colors.blue,
              height: 400,
              child:  QRView(
                key: qrKey,
                onQRViewCreated: _onQRViewCreated,
              ),
            ),
            Container(
              margin: EdgeInsets.only(top: 36),
              child: Text(
                'Problem to scan QR?',
                textAlign: TextAlign.center,
                style: GoogleFonts.epilogue(
                    textStyle: TextStyle(
                      fontSize: 14,
                      fontWeight: FontWeight.w500,
                      color: Colors.black,
                      fontStyle: FontStyle.normal,
                    )
                ),
              ),
            ),
            Container(
              margin: EdgeInsets.only(top: 5),
              child: Text(
                'Click Here',
                textAlign: TextAlign.center,
                style: GoogleFonts.epilogue(
                    textStyle: TextStyle(
                      fontSize: 14,
                      fontWeight: FontWeight.w500,
                      color: Colors.black,
                      fontStyle: FontStyle.normal,
                    )
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

  void _onQRViewCreated(QRViewController controller) {
    this.controller = controller;
    controller.scannedDataStream.listen((scanData) {
      setState(() {
        result = scanData;
      });
    });
  }
}

And here is the error: Error shown

Appreciated if someone could help me cheers

It should close the camera first before going to previous page.

Answer 1

Instead of doing super.dispose(); inside WillPopScope, you can override the dispose method on state class.

class _QRScanState extends State<QRScan> {
  .....
  @override
  void dispose() {
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        await controller?.stopCamera();
        //not here
        return true;
      },
      child: Scaffold(