Render QrView in Dialog

QrDialog.dart

import 'package:flutter/material.dart';
import 'package:deshario/components/ScannerOverlay.dart';
import 'package:qr_code_scanner/qr_code_scanner.dart';

class QrDialog extends StatefulWidget {

  final String dialogTitle;
  final ValueChanged<String> onGetResult;

  QrDialog({
    @required this.dialogTitle,
    @required this.onGetResult
  });

  @override
  QrDialogState createState() => QrDialogState();
}

class QrDialogState extends State<QrDialog> {
  final GlobalKey mqrKey = GlobalKey(debugLabel: 'mQR');

  QRViewController controller;

  Widget renderQr(){
    return Stack(
      children: [
        QRView(
          key: mqrKey,
          overlay: ScannerOverlay(
              borderColor: Colors.white,
              borderLength: 40,
              borderWidth: 5,
              cutOutSize: 280
          ),
          onQRViewCreated: _onQRViewCreate),
      ],
    );
  }

  Dialog dialogContent(mContext){
    return Dialog(
      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(3)),
      child: Container(
        width: MediaQuery.of(context).size.width * 1,
        height: MediaQuery.of(context).size.height * 0.45,
        color: Colors.transparent,
        child: Column(
          children: <Widget>[
            Expanded(
              flex: 1,
              child: Center(
                child: Text('${widget.dialogTitle}', style: TextStyle(fontSize: 20)),
              ),
            ),
            Expanded(
              flex: 5,
              child: QRView(
                key: GlobalKey(debugLabel: 'order.getKey()'),
                overlay: ScannerOverlay(
                  borderColor: Colors.white,
                  borderLength: 40,
                  borderWidth: 5,
                  cutOutSize: 250
                ),
                onQRViewCreated: _onQRViewCreate
              ),
            ),
          ],
        )
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return dialogContent(context);
  }

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

  void _onQRViewCreate(QRViewController controller) {
    this.controller = controller;
    controller.scannedDataStream.listen((scanData){
      widget.onGetResult(scanData);
    });
  }
}

ScannerOverlay.dart

import 'dart:ui';

import 'package:flutter/material.dart';

class ScannerOverlay extends ShapeBorder {
  final Color borderColor;
  final double borderWidth;
  final Color overlayColor;
  final double borderRadius;
  final double borderLength;
  final double cutOutSize;

  ScannerOverlay({
    this.borderColor = Colors.red,
    this.borderWidth = 3.0,
    this.overlayColor = const Color.fromRGBO(0, 0, 0, 80),
    this.borderRadius = 0,
    this.borderLength = 40,
    this.cutOutSize = 250,
  }) : assert(
            cutOutSize != null
                ? cutOutSize != null
                    ? borderLength <= cutOutSize / 2 + borderWidth * 2
                    : true
                : true,
            "Border can't be larger than ${cutOutSize / 2 + borderWidth * 2}");

  @override
  EdgeInsetsGeometry get dimensions => const EdgeInsets.all(10.0);

  @override
  Path getInnerPath(Rect rect, {TextDirection textDirection}) {
    return Path()
      ..fillType = PathFillType.evenOdd
      ..addPath(getOuterPath(rect), Offset.zero);
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection textDirection}) {
    Path _getLeftTopPath(Rect rect) {
      return Path()
        ..moveTo(rect.left, rect.bottom)
        ..lineTo(rect.left, rect.top)
        ..lineTo(rect.right, rect.top);
    }

    return _getLeftTopPath(rect)
      ..lineTo(
        rect.right,
        rect.bottom,
      )
      ..lineTo(
        rect.left,
        rect.bottom,
      )
      ..lineTo(
        rect.left,
        rect.top,
      );
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection textDirection}) {
    final width = rect.width;
    final borderWidthSize = width / 2;
    final height = rect.height;
    final borderOffset = borderWidth / 2;
    final _borderLength = borderLength > cutOutSize / 2 + borderWidth * 2
        ? borderWidthSize / 2
        : borderLength;
    final _cutOutSize = cutOutSize != null && cutOutSize < width
        ? cutOutSize
        : width - borderOffset;

    final backgroundPaint = Paint()
      ..color = overlayColor
      ..style = PaintingStyle.fill;

    final borderPaint = Paint()
      ..color = borderColor
      ..style = PaintingStyle.stroke
      ..strokeWidth = borderWidth;

    final boxPaint = Paint()
      ..color = borderColor
      ..style = PaintingStyle.fill
      ..blendMode = BlendMode.dstOut;

    final cutOutRect = Rect.fromLTWH(
      rect.left + width / 2 - _cutOutSize / 2 + borderOffset,
      rect.top + height / 2 - _cutOutSize / 2 + borderOffset,
      _cutOutSize - borderOffset * 2,
      _cutOutSize - borderOffset * 2,
    );

    canvas.saveLayer(
      rect,
      backgroundPaint,
    );

    canvas
      ..drawRect(
        rect,
        backgroundPaint,
      )
      // Draw top right corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.right - _borderLength,
          cutOutRect.top,
          cutOutRect.right,
          cutOutRect.top + _borderLength,
          topRight: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      // Draw top left corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.left,
          cutOutRect.top,
          cutOutRect.left + _borderLength,
          cutOutRect.top + _borderLength,
          topLeft: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      // Draw bottom right corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.right - _borderLength,
          cutOutRect.bottom - _borderLength,
          cutOutRect.right,
          cutOutRect.bottom,
          bottomRight: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      // Draw bottom left corner
      ..drawRRect(
        RRect.fromLTRBAndCorners(
          cutOutRect.left,
          cutOutRect.bottom - _borderLength,
          cutOutRect.left + _borderLength,
          cutOutRect.bottom,
          bottomLeft: Radius.circular(borderRadius),
        ),
        borderPaint,
      )
      ..drawRRect(
        RRect.fromRectAndRadius(
          cutOutRect,
          Radius.circular(borderRadius),
        ),
        boxPaint,
      )
      ..restore();
  }

  @override
  ShapeBorder scale(double t) {
    return ScannerOverlay(
      borderColor: borderColor,
      borderWidth: borderWidth,
      overlayColor: overlayColor,
    );
  }
}