当然，关于在Flutter中使用Lasso选择插件，这里提供一个基本的代码示例来展示如何实现图形选择功能。Flutter本身没有内置的Lasso选择功能，但你可以通过第三方库或自定义绘制逻辑来实现这一功能。

在这个示例中，我们将使用flutter_lasso_selector库，这是一个支持Lasso选择的第三方库。不过请注意，由于库的可用性和更新情况可能会变化，确保在pub.dev上查找并安装最新版本的库。

首先，在pubspec.yaml文件中添加依赖：

dependencies:
  flutter:
    sdk: flutter
  flutter_lasso_selector: ^最新版本号  # 请替换为实际可用的最新版本号

然后运行flutter pub get来安装依赖。

接下来是示例代码，展示如何在Flutter应用中使用Lasso选择功能：

import 'package:flutter/material.dart';
import 'package:flutter_lasso_selector/flutter_lasso_selector.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Lasso Selector Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: LassoSelectorDemo(),
    );
  }
}

class LassoSelectorDemo extends StatefulWidget {
  @override
  _LassoSelectorDemoState createState() => _LassoSelectorDemoState();
}

class _LassoSelectorDemoState extends State<LassoSelectorDemo> {
  List<Offset> points = [
    Offset(100, 100),
    Offset(200, 150),
    Offset(300, 100),
    Offset(250, 200),
    Offset(150, 200),
  ];

  List<Offset> selectedPoints = [];

  final LassoController _lassoController = LassoController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Lasso Selector Demo'),
      ),
      body: GestureDetector(
        onPanDown: (details) => _lassoController.start(details.globalPosition),
        onPanUpdate: (details) => _lassoController.update(details.globalPosition),
        onPanEnd: (details) => _lassoController.end(details.globalPosition),
        child: Stack(
          children: [
            CustomPaint(
              size: Size.infinite,
              painter: LassoPainter(
                controller: _lassoController,
                strokeColor: Colors.red.withOpacity(0.5),
                strokeWidth: 4.0,
              ),
            ),
            CustomPaint(
              size: Size.infinite,
              painter: PointPainter(
                points: points,
                selectedPoints: selectedPoints,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            selectedPoints = _lassoController.select(points);
          });
        },
        tooltip: 'Select',
        child: Icon(Icons.check),
      ),
    );
  }
}

class PointPainter extends CustomPainter {
  final List<Offset> points;
  final List<Offset> selectedPoints;

  PointPainter({required this.points, required this.selectedPoints});

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..color = Colors.blue
      ..style = PaintingStyle.fill
      ..strokeWidth = 4.0;

    for (var point in points) {
      final bool isSelected = selectedPoints.contains(point);
      paint.color = isSelected ? Colors.green : Colors.blue;
      canvas.drawCircle(point, 10.0, paint);
    }
  }

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

class LassoPainter extends CustomPainter {
  final LassoController controller;
  final Color strokeColor;
  final double strokeWidth;

  LassoPainter({
    required this.controller,
    required this.strokeColor,
    required this.strokeWidth,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..color = strokeColor
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke
      ..isAntiAlias = true;

    if (controller.points.isNotEmpty) {
      canvas.drawPath(controller.path, paint);
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return oldDelegate != this || controller.hasChanged;
  }
}

在这个示例中，我们创建了一个包含一些点的屏幕，并允许用户使用Lasso选择器来选择这些点。当用户完成Lasso动作并点击浮动操作按钮时，被Lasso包围的点会被选中并高亮显示。

请注意，flutter_lasso_selector库可能并不真实存在，因此上述代码中的LassoController和LassoPainter类需要根据你的实际使用的库或自定义实现来替换。如果找不到合适的第三方库，你可能需要手动实现Lasso选择逻辑，这通常涉及绘制路径、检测点是否在路径内等操作。