1. 定义一个class

class MyPainter extends CustomPainter {  Color lineColor;  double width;  MyPainter({
    this.lineColor, this.width});  @override  void paint(Canvas canvas, Size size) {    Paint _paint = new Paint()    ..color = Colors.blueAccent    ..strokeCap = StrokeCap.round    ..isAntiAlias = true    ..strokeWidth = 5.0    ..style = PaintingStyle.stroke;    canvas.drawLine(Offset(20.0, 20.0), Offset(100.0, 100.0), _paint);  }  @override  bool shouldRepaint(CustomPainter oldDelegate) => false;}

2. 使用

Container(    child:CustomPaint(        foregroundPainter: new MyPainter(             lineColor: Colors.lightBlueAccent,             width: 8.0,       ),    ),),