Flutter绘制弧线

如图所示，实现带弧度的容器，用

CustomPaint实现，直接上代码

import 'dart:math';import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';void main() {runApp(MyApp());
}class MyApp extends StatelessWidget {// This widget is the root of your application.@overrideWidget build(BuildContext context) {return MaterialApp(title: 'Flutter Demo',theme: ThemeData(// This is the theme of your application.//// Try running your application with "flutter run". You'll see the// application has a blue toolbar. Then, without quitting the app, try// changing the primarySwatch below to Colors.green and then invoke// "hot reload" (press "r" in the console where you ran "flutter run",// or simply save your changes to "hot reload" in a Flutter IDE).// Notice that the counter didn't reset back to zero; the application// is not restarted.primarySwatch: Colors.blue,// This makes the visual density adapt to the platform that you run// the app on. For desktop platforms, the controls will be smaller and// closer together (more dense) than on mobile platforms.visualDensity: VisualDensity.adaptivePlatformDensity,),home: MyHomePage(title: 'Flutter Demo Home Page'),);}
}class MyHomePage extends StatefulWidget {MyHomePage({Key key, this.title}) : super(key: key);// This widget is the home page of your application. It is stateful, meaning// that it has a State object (defined below) that contains fields that affect// how it looks.// This class is the configuration for the state. It holds the values (in this// case the title) provided by the parent (in this case the App widget) and// used by the build method of the State. Fields in a Widget subclass are// always marked "final".final String title;@override_MyHomePageState createState() => _MyHomePageState();
}class _MyHomePageState extends State<MyHomePage> {int _counter = 0;void _incrementCounter() {setState(() {// This call to setState tells the Flutter framework that something has// changed in this State, which causes it to rerun the build method below// so that the display can reflect the updated values. If we changed// _counter without calling setState(), then the build method would not be// called again, and so nothing would appear to happen._counter++;});}@overrideWidget build(BuildContext context) {// This method is rerun every time setState is called, for instance as done// by the _incrementCounter method above.//// The Flutter framework has been optimized to make rerunning build methods// fast, so that you can just rebuild anything that needs updating rather// than having to individually change instances of widgets.return Scaffold(appBar: AppBar(// Here we take the value from the MyHomePage object that was created by// the App.build method, and use it to set our appbar title.title: Text(widget.title),),body: Center(// Center is a layout widget. It takes a single child and positions it// in the middle of the parent.child: Column(mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[Text('You have pushed the button this many times:',),Text('$_counter',style: Theme.of(context).textTheme.headline4,),Container(height: 100,color: Colors.red,child: CustomPaint(painter: Sky(),child: Center(child: Text('',style: const TextStyle(fontSize: 40.0,fontWeight: FontWeight.w900,color: Color(0xFFFFFFFF),),),),))],),),floatingActionButton: FloatingActionButton(onPressed: _incrementCounter,tooltip: 'Increment',child: Icon(Icons.add),), // This trailing comma makes auto-formatting nicer for build methods.);}
}class Sky extends CustomPainter {Paint _paint = Paint()..color = Colors.red //画笔颜色..strokeCap = StrokeCap.butt //画笔笔触类型// ..isAntiAlias = true //是否启动抗锯齿// ..blendMode = BlendMode.exclusion //颜色混合模式..style = PaintingStyle.fill //绘画风格，默认为填充// ..colorFilter = ColorFilter.mode(Colors.redAccent,//     BlendMode.exclusion) //颜色渲染模式，一般是矩阵效果来改变的,但是flutter中只能使用颜色混合模式// ..maskFilter = MaskFilter.blur(BlurStyle.inner, 3.0) //模糊遮罩效果，flutter中只有这个..filterQuality = FilterQuality.high //颜色渲染模式的质量..strokeWidth = 1.0; //@overridevoid paint(Canvas canvas, Size size) {// Path path = new Path();// path.moveTo(0, 0);// path.lineTo(100, 100);// path.lineTo(200, 200);// path.lineTo(0, 0);// path.close();// canvas.drawPath(path, _paint);// canvas.drawCircle(Offset(100, 100), 50, _paint);canvas.drawLine(Offset(20.0, 20.0), Offset(100.0, 100.0), _paint);const PI = 3.1415926;// Rect rect2 = Rect.fromCircle(center: Offset(100.0, 50.0), radius: 200.0);// canvas.drawArc(rect2, -PI, PI, false, _paint,);// Rect rect1 = Rect.fromPoints(Offset(150.0, 200.0), Offset(300.0, 250.0));// canvas.drawOval(rect1, _paint);var startPoint = Offset(0, size.height); 开始位置var controlPoint1 = Offset(size.width / 4, size.height / 3 * 4); 控制点var controlPoint2 = Offset(3 * size.width / 4, size.height / 3 * 4);控制点var endPoint = Offset(size.width, size.height);结束位置var path = Path();path.moveTo(startPoint.dx, startPoint.dy);path.cubicTo(controlPoint1.dx, controlPoint1.dy,controlPoint2.dx, controlPoint2.dy,endPoint.dx, endPoint.dy);canvas.drawPath(path, _paint);}@overridebool shouldRepaint(Sky oldDelegate) => false;@overridebool shouldRebuildSemantics(Sky oldDelegate) => false;
}

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