Pass a class as method parameter in Dart - flutter

Question

Suppose this class:
class SimpleRectPaint extends Object {
static CustomPaint build( ParamsBundle paramBundle ) {
return CustomPaint(
painter: SimpleRectPainter( paramBundle: paramBundle ),
child: Container(width: paramBundle.width, height: paramBundle.height)
);
}
}
I'd like to abstract the class SimpleRectPaint by means of a ClassReference parameter someClass and make the method more generic. Unfortunately, this isn't valid code:
class SimpleRectPaint extends Object {
static CustomPaint build( ParamsBundle paramBundle, ClassReference someClass ) {
return CustomPaint(
painter: someClass( paramBundle: paramBundle ),
child: Container(width: paramBundle.width, height: paramBundle.height)
);
}
}
Q: How do I have to write it instead?

Answer 1

You could do that by passing a CustomPainterCreator:
import 'package:flutter/material.dart';
void main() {
runApp(
MaterialApp(
title: 'Generic Painter',
home: Scaffold(
body: MyWidget(),
),
),
);
}
class MyWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Center(
child: SizedBox(
width: 200,
height: 200,
child: Stack(
fit: StackFit.expand,
children: [
Background(),
MyPainter(creator: RectPainter.creator, color: Color(0xFF104C91)),
MyPainter(creator: OvalPainter.creator, color: Color(0xFF1F8AC0)),
],
),
),
);
}
}
class Background extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Container(
decoration: BoxDecoration(
color: Color(0xFFEFC9AF),
border: Border.all(width: 3.0),
borderRadius: BorderRadius.all(Radius.circular(10.0)),
),
);
}
}
typedef CustomPainterCreator(Color color);
class MyPainter extends StatelessWidget {
final CustomPainterCreator creator;
final Color color;
const MyPainter({
Key key,
this.creator,
this.color,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return CustomPaint(
painter: creator(color),
);
}
}
class OvalPainter extends CustomPainter {
static CustomPainterCreator creator = (color) => OvalPainter(color: color);
final Color color;
OvalPainter({this.color = Colors.green});
#override
void paint(Canvas canvas, Size size) {
final paint = Paint()..color = color;
canvas.drawOval(
Rect.fromLTWH(size.width * .4, size.height * .15, size.width * .5,
size.height * .5),
paint,
);
}
#override
bool shouldRepaint(OvalPainter oldDelegate) => false;
}
class RectPainter extends CustomPainter {
static CustomPainterCreator creator = (color) => RectPainter(color: color);
final Color color;
RectPainter({this.color = Colors.indigo});
#override
void paint(Canvas canvas, Size size) {
final paint = Paint()..color = color;
canvas.drawRRect(
RRect.fromRectAndRadius(
Rect.fromLTWH(size.width * .15, size.height * .25, size.width * .6,
size.height * .6),
Radius.circular(20)),
paint,
);
}
#override
bool shouldRepaint(RectPainter oldDelegate) => false;
}
But, though the exercise is interesting... Why?
Instead of:
MyPainter(creator: RectPainter.creator, color: Color(0xFF104C91)),
You can just do:
CustomPaint(painter: RectPainter(color: Color(0xFF104C91))),
If, not, what is the specific needs that would require more abstraction?