Flutter 中画圆

问题：

Flutter 中如何画圆？

解决方法：

创建一个 StatelessWidget 叫做 MyArc,  接收一个直径的参数：

class MyArc extends StatelessWidget {
  final double diameter;

  const MyArc({Key key, this.diameter = 200}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: MyPainter(),
      size: Size(diameter, diameter),
    );
  }
}

// This is the Painter class
class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = Paint()..color = Colors.blue;
    canvas.drawArc(
      Rect.fromCenter(
        center: Offset(size.height / 2, size.width / 2),
        height: size.height,
        width: size.width,
      ),
      math.pi,
      math.pi,
      false,
      paint,
    );
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}