flutter: CustomPaint widget turned blank when put in a Column - flutter

Question

I've got something super bizarre:
The following code paints a rectangle with CustomPaint. This version works fine
import 'package:flutter/material.dart';
class MyApp extends StatefulWidget {
#override
_ MyAppState createState() => _ MyAppState();
}
class _MyAppState extends State<MyApp> {
EmbeddedPainter _painter;
#override
void initState() {
super.initState();
_painter = EmbeddedPainter();
}
#override
Widget build(BuildContext context) {
return Container(
child: ClipRect(
child: CustomPaint(
painter: _painter
),
),
);
}
}
Then as soon as I place this CustomPaint into a Column widget, I no longer see the painted rectangle.
import 'package:flutter/material.dart';
class MyApp extends StatefulWidget {
#override
_ MyAppState createState() => _ MyAppState();
}
class _MyAppState extends State<MyApp> {
EmbeddedPainter _painter;
#override
void initState() {
super.initState();
_painter = EmbeddedPainter();
}
#override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
ClipRect(
child: CustomPaint(
painter: _painter
),
),
],
)
);
}
}
The painter looks like this
class EmbeddedPainter extends CustomPainter with ChangeNotifier {
var _paint = Paint()
..strokeJoin = StrokeJoin.miter
..strokeWidth = 1.0
..color = Colors.green
..style = PaintingStyle.fill;
#override
void paint(Canvas canvas, Size size) {
canvas.drawRect(Rect.fromLTWH(50, 50, 100, 100), _paint);
}
#override
bool shouldRepaint(CustomPainter oldDelegate) => true;
void update(Color color0, Color color1) {
// draw
notifyListeners();
}
}

Answer 1

Solved it myself:
The ClipRect must be wrapped with a container with size, e.g., a SizedBox.
#override
Widget build(BuildContext context) {
return Container(
child: Column(
children: <Widget>[
SizedBox(
width: 500,
height: 300,
child: ClipRect(
child: CustomPaint(
painter: _painter
),
),
)
],
)
);
}