Flutter绘制弯曲虚线

效果

开始

修改main.dart文件:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Drawing Shapes",
      home: DrawingPage(),
    );
  }
}

class DrawingPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Curved Line"),
      ),
      body: CustomPaint(
        painter: CurvePainter(),
        child: Container(),
      ),
    );
  }
}

class CurvePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {

  }

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

接下来我们在CurvePainter中实现绘制:

这里使用贝塞尔曲线绘制,需要4个点,分别是:起点,终点和两个控制点,像图中那样,移动控制点就能改变曲线形状。你可以在在线工具中尝试:

我们使用 cubicTo方法设置路径path:

void cubicTo(double x1, double y1, double x2, double y2, double x3, double y3)

函数绘制路径从当前点到(x3,y3),控制点是(x1,y1),(x2,y2)

正如你看到的,cubicTo 方法接受3个点作为参数,前两个代表控制点,最后一个是结束点。开始点就是你的pen当前坐在canvas中的点。

canvas的坐标系是左上角是(0,0)。右下角是(size.width, size.height)。所以可以尝试调整4个点:

void paint(Canvas canvas, Size size) {

  var paint = Paint();

  paint.color = Colors.lightBlue;
  paint.style = PaintingStyle.stroke;
  paint.strokeWidth = 3;

  var startPoint = Offset(0, size.height / 2);
  var controlPoint1 = Offset(size.width / 4, size.height / 3);
  var controlPoint2 = Offset(3 * size.width / 4, size.height / 3);
  var endPoint = Offset(size.width, size.height / 2);

  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);
}

paint对象就是相当于我们的笔,被设置了蓝色和宽度为3.

我们使用path表述贝塞尔曲线。moveTo方法移动笔到开始点的位置。最后使用drawPath方法绘制出来。

虚线

可以是使用三方库绘制虚线:https://pub.dartlang.org/packages/path_drawing

要使用它现在 pubspec.yml文件添加这个库:

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  path_drawing: ^0.4.0

运行“flutter packages get”获得库,然后导入头文件就可以使用了:

import 'package:path_drawing/path_drawing.dart';

把上面的路径用dashPath包裹一下就可以了:

canvas.drawPath(
  dashPath(
    path,
    dashArray: CircularIntervalList<double>(<double>[15.0, 10.5]),
  ),
  paint,
);

dashPath方法接受两个参数,第一个就是要绘制的path,第二个参数定义每一段虚线的长度和两个虚线间的间隔长度。结果如下:

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