Draw lines with flutter

Question

Is there any way to display skew borders at the top and bottom? I came up with the solution below by using two images (top_layout and bottom_layout.png). Is there any other way to make those color bars with shadows without using static images?

return Container(
      color: const Color.fromARGB(255, 236, 0, 140),
      child: Container(
        padding: const EdgeInsets.all(8.0),
        child: Container(
          color: Colors.white,
          margin:
              EdgeInsets.only(top: 60.0, bottom: 20.0, left: 15.0, right: 15.0),
          child: Stack(
            children: <Widget>[
              Positioned.fill(
                child: Image.asset(
                  "assets/imgs/top_layout.png",
                  fit: BoxFit.fitWidth,
                  alignment: Alignment.topCenter,
                ),
              ),
              Positioned.fill(
                child: Image.asset(
                  "assets/imgs/xbottom_layout.png",
                  fit: BoxFit.fitWidth,
                  alignment: Alignment.bottomLeft,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }

Answer 1

How do draw lines in Flutter using the CustomPaint widget

To paint in Flutter you use the CustomPaint widget. The CustomPaint widget takes a CustomPainter object as a parameter. In that class you have to override the paint method, which gives you a canvas that you can paint on. Here is the code to draw the line in the image above.

@override
void paint(Canvas canvas, Size size) {
  final p1 = Offset(50, 50);
  final p2 = Offset(250, 150);
  final paint = Paint()
    ..color = Colors.black
    ..strokeWidth = 4;
  canvas.drawLine(p1, p2, paint);
}

Notes:

• The drawLine method draws a line connecting the two points you give it.
• An Offset is a pair of (dx, dy) doubles, offset from the top left corner of the CustomPaint widget.

Another option

You could do something similar with the drawPoints method using the PointMode.polygon option.

@override
void paint(Canvas canvas, Size size) {
  final pointMode = ui.PointMode.polygon;
  final points = [
    Offset(50, 100),
    Offset(150, 75),
    Offset(250, 250),
    Offset(130, 200),
    Offset(270, 100),
  ];
  final paint = Paint()
    ..color = Colors.black
    ..strokeWidth = 4
    ..strokeCap = StrokeCap.round;
  canvas.drawPoints(pointMode, points, paint);
}

Context

Here is the main.dart code so that you can see it in context.

import 'dart:ui' as ui;
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: HomeWidget(),
      ),
    );
  }
}

class HomeWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: CustomPaint( //                       <-- CustomPaint widget
        size: Size(300, 300),
        painter: MyPainter(),
      ),
    );
  }
}

class MyPainter extends CustomPainter { //         <-- CustomPainter class
  @override
  void paint(Canvas canvas, Size size) {
    //                                             <-- Insert your painting code here.
  }

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

See also

See this article for my fuller answer.