r_scan/example/lib/scan_dialog.dart

import 'package:flutter/material.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:r_scan/r_scan.dart';

class RScanDialog extends StatefulWidget {
  @override
  _RScanDialogState createState() => _RScanDialogState();
}

class _RScanDialogState extends State<RScanDialog> {
  RScanController _controller;

  @override
  void initState() {
    super.initState();
    initController();
  }

  bool isFirst = true;

  Future<void> initController() async {
    _controller = RScanController();
    _controller.addListener(() {
      final result = _controller.result;
      if (result != null) {
        if (isFirst) {
          Navigator.of(context).pop(result);
          isFirst = false;
        }
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: FutureBuilder<bool>(
        future: canOpenCameraView(),
        builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
          if (snapshot.hasData && snapshot.data == true) {
            return Stack(
              children: <Widget>[
                ScanImageView(
                  child: RScanView(
                    controller: _controller,
                  ),
                ),
                Align(
                    alignment: Alignment.bottomCenter,
                    child: FutureBuilder(
                      future: getFlashMode(),
                      builder: _buildFlashBtn,
                    ))
              ],
            );
          } else {
            return Container();
          }
        },
      ),
    );
  }

  Future<bool> getFlashMode() async {
    bool isOpen = false;
    try {
      isOpen = await _controller.getFlashMode();
    } catch (_) {}
    return isOpen;
  }

  Future<bool> canOpenCameraView() async {
    var status =
        await PermissionHandler().checkPermissionStatus(PermissionGroup.camera);
    if (status != PermissionStatus.granted) {
      var future = await PermissionHandler()
          .requestPermissions([PermissionGroup.camera]);
      for (final item in future.entries) {
        if (item.value != PermissionStatus.granted) {
          return false;
        }
      }
    } else {
      return true;
    }
    return true;
  }

  Widget _buildFlashBtn(BuildContext context, AsyncSnapshot<bool> snapshot) {
    return snapshot.hasData
        ? Padding(
            padding: EdgeInsets.only(
                bottom: 24 + MediaQuery.of(context).padding.bottom),
            child: IconButton(
                icon: Icon(snapshot.data ? Icons.flash_on : Icons.flash_off),
                color: Colors.white,
                iconSize: 46,
                onPressed: () {
                  if (snapshot.data) {
                    _controller.setFlashMode(false);
                  } else {
                    _controller.setFlashMode(true);
                  }
                  setState(() {});
                }),
          )
        : Container();
  }
}

class ScanImageView extends StatefulWidget {
  final Widget child;

  const ScanImageView({Key key, this.child}) : super(key: key);

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

class _ScanImageViewState extends State<ScanImageView>
    with TickerProviderStateMixin {
  AnimationController controller;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
        vsync: this, duration: Duration(milliseconds: 1000));
    controller.repeat(reverse: true);
  }

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

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
        animation: controller,
        builder: (BuildContext context, Widget child) => CustomPaint(
              foregroundPainter:
                  _ScanPainter(controller.value, Colors.white, Colors.green),
              child: widget.child,
              willChange: true,
            ));
  }
}

class _ScanPainter extends CustomPainter {
  final double value;
  final Color borderColor;
  final Color scanColor;

  _ScanPainter(this.value, this.borderColor, this.scanColor);

  Paint _paint;

  @override
  void paint(Canvas canvas, Size size) {
    if (_paint == null) {
      initPaint();
    }
    double width = size.width;
    double height = size.height;

    double boxWidth = size.width * 2 / 3;
    double boxHeight = height / 4;

    double left = (width - boxWidth) / 2;
    double top = boxHeight;
    double bottom = boxHeight * 2;
    double right = left + boxWidth;
    _paint.color = borderColor;
    final rect = Rect.fromLTWH(left, top, boxWidth, boxHeight);
    canvas.drawRect(rect, _paint);

    _paint.strokeWidth = 3;

    Path path1 = Path()
      ..moveTo(left, top + 10)
      ..lineTo(left, top)
      ..lineTo(left + 10, top);
    canvas.drawPath(path1, _paint);
    Path path2 = Path()
      ..moveTo(left, bottom - 10)
      ..lineTo(left, bottom)
      ..lineTo(left + 10, bottom);
    canvas.drawPath(path2, _paint);
    Path path3 = Path()
      ..moveTo(right, bottom - 10)
      ..lineTo(right, bottom)
      ..lineTo(right - 10, bottom);
    canvas.drawPath(path3, _paint);
    Path path4 = Path()
      ..moveTo(right, top + 10)
      ..lineTo(right, top)
      ..lineTo(right - 10, top);
    canvas.drawPath(path4, _paint);

    _paint.color = scanColor;

    final scanRect = Rect.fromLTWH(
        left + 10, top + 10 + (value * (boxHeight - 20)), boxWidth - 20, 3);

    _paint.shader = LinearGradient(colors: <Color>[
      Colors.white54,
      Colors.white,
      Colors.white54,
    ], stops: [
      0.0,
      0.5,
      1,
    ]).createShader(scanRect);
    canvas.drawRect(scanRect, _paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }

  void initPaint() {
    _paint = Paint()
      ..style = PaintingStyle.stroke
      ..strokeWidth = 1
      ..isAntiAlias = true
      ..strokeCap = StrokeCap.round
      ..strokeJoin = StrokeJoin.round;
  }
}