How to create a dotted border around a box in flutter?

Question

I am building a list of boxes layouts in my app using flutter. I want dotted border around the box. I have used card widget to create the boxes. But, how can I get dotted border around the boxes?

Answer 1

EDIT

I have added this as a package in pub.

Now, all you need to do is

DottedBorder(
  color: Colors.black,
  gap: 3,
  strokeWidth: 1,
  child: FlutterLogo(size: 148),
)

Working Solution [Outdated]

Like tomerpacific said in this answer, Flutter does not have a default implementation for dashed border at the moment.

I worked for some time yesterday and was able to come up with a solution using CustomPainter. Hope this helps someone.

Add the DashedRect to your container, like so

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          height: 400,
          width: 300,
          color: Colors.black12,
          child: DashedRect(color: Colors.red, strokeWidth: 2.0, gap: 3.0,),
        ),
      ),
    );
  }
}

DashedRect.dart

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

class DashedRect extends StatelessWidget {
  final Color color;
  final double strokeWidth;
  final double gap;

  DashedRect(
      {this.color = Colors.black, this.strokeWidth = 1.0, this.gap = 5.0});

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Padding(
        padding: EdgeInsets.all(strokeWidth / 2),
        child: CustomPaint(
          painter:
              DashRectPainter(color: color, strokeWidth: strokeWidth, gap: gap),
        ),
      ),
    );
  }
}

class DashRectPainter extends CustomPainter {
  double strokeWidth;
  Color color;
  double gap;

  DashRectPainter(
      {this.strokeWidth = 5.0, this.color = Colors.red, this.gap = 5.0});

  @override
  void paint(Canvas canvas, Size size) {
    Paint dashedPaint = Paint()
      ..color = color
      ..strokeWidth = strokeWidth
      ..style = PaintingStyle.stroke;

    double x = size.width;
    double y = size.height;

    Path _topPath = getDashedPath(
      a: math.Point(0, 0),
      b: math.Point(x, 0),
      gap: gap,
    );

    Path _rightPath = getDashedPath(
      a: math.Point(x, 0),
      b: math.Point(x, y),
      gap: gap,
    );

    Path _bottomPath = getDashedPath(
      a: math.Point(0, y),
      b: math.Point(x, y),
      gap: gap,
    );

    Path _leftPath = getDashedPath(
      a: math.Point(0, 0),
      b: math.Point(0.001, y),
      gap: gap,
    );

    canvas.drawPath(_topPath, dashedPaint);
    canvas.drawPath(_rightPath, dashedPaint);
    canvas.drawPath(_bottomPath, dashedPaint);
    canvas.drawPath(_leftPath, dashedPaint);
  }

  Path getDashedPath({
    @required math.Point<double> a,
    @required math.Point<double> b,
    @required gap,
  }) {
    Size size = Size(b.x - a.x, b.y - a.y);
    Path path = Path();
    path.moveTo(a.x, a.y);
    bool shouldDraw = true;
    math.Point currentPoint = math.Point(a.x, a.y);

    num radians = math.atan(size.height / size.width);

    num dx = math.cos(radians) * gap < 0
        ? math.cos(radians) * gap * -1
        : math.cos(radians) * gap;

    num dy = math.sin(radians) * gap < 0
        ? math.sin(radians) * gap * -1
        : math.sin(radians) * gap;

    while (currentPoint.x <= b.x && currentPoint.y <= b.y) {
      shouldDraw
          ? path.lineTo(currentPoint.x, currentPoint.y)
          : path.moveTo(currentPoint.x, currentPoint.y);
      shouldDraw = !shouldDraw;
      currentPoint = math.Point(
        currentPoint.x + dx,
        currentPoint.y + dy,
      );
    }
    return path;
  }

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

I do not expect this to fit in with all use cases and there is a lot of room for customization and improvement. Comment if you find any bugs.

Answer 2

Here is a fdottedline flutter package to easily added dotted borders around widgets. This use the easiest way to create a dotted line view and provides developers with the ability to create dashed lines. It also supports creating a dashed border for a [Widget]. Support for controlling the thickness, spacing, and corners of the dotted border.

1. To use this package, add fdottedline as a dependency in your pubspec.yaml file.

2. Usage: Dotted Shape Demo

   FDottedLine(
     color: Colors.lightBlue[600],
     height: 100.0,
     width: 50,
     strokeWidth: 2.0,
     dottedLength: 10.0,
     space: 2.0,
   )
   

Answer 3

You can use dotted_border Flutter package

return DottedBorder(
   borderType: BorderType.RRect,
   radius: Radius.circular(20),
   dashPattern: [10, 10],
   color: Colors.grey,
   strokeWidth: 2,
   child: Card(
       color: Colors.amber,
       shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(10),
       ),
       child: Center(child: Text("hi")),
   )

Answer 4

There is an one plugin for draw dotted border around widgets

https://pub.dev/packages/dotted_border

Using this plugin you can draw dotted or dashed border

//1. Install the plugin by add dependencies in pubspace.yaml
dotted_border: ^1.0.6

Add below code for show border

DottedBorder(
color: Colors.black,
strokeWidth: 1,
child: FlutterLogo(size: 148),
)

Answer 5

Currently, there is no support for a dashed border in Flutter, since there are only two styles:

Solid or None

To add a border to your widget you need to do the following:

• Add a BoxDecoration property to your widget

• Part of the properties of BoxDecoration is border

   decoration: BoxDecoration(
    border: Border.all(
       width: 1,
       style: BorderStyle.solid/none
     ),
   );
  

I also found out this SO question which demonstrates how to add a circular dashed border.