Flutter: Failed assertion: line 1927 pos 12: 'hasSize' - flutter

Question

I want to add an image in the background. I found this code snippet here in StackOverflow.
SizedBox.expand(
// -> 01
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: NetworkImage(
'https://wallpapercave.com/wp/wp5561184.jpg'),
fit: BoxFit.cover, // -> 02
),
),
),
),
this worked quite well for me in this code:
enter codeimport 'package:flutter/material.dart';
class Welcome extends StatelessWidget {
final int _picState;
final VoidCallback _picStateChange;
final Function _quizStarted;
Welcome(this._quizStarted, this._picState, this._picStateChange);
#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
alignment: AlignmentDirectional.bottomCenter,
children: [
SizedBox.expand(
// -> 01
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: NetworkImage(
'https://wallpapercave.com/wp/wp5561184.jpg'),
fit: BoxFit.cover, // -> 02
),
),
),
),
SafeArea(
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 20),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
const Spacer(),
Text(
'Start Application',
style: Theme.of(context).textTheme.headline3?.copyWith(
color: Colors.white54,
fontWeight: FontWeight.bold,
),
textAlign: TextAlign.center,
),
Spacer(),
Spacer(),
TextField(
onTap: () => _picStateChange(),
decoration: InputDecoration(
focusColor: Colors.amber,
filled: true,
fillColor: Colors.white.withOpacity(0.2),
hintText: 'ENTER YOUR NAME HERE',
hintStyle: TextStyle(
wordSpacing: 2,
fontWeight: FontWeight.bold,
color: Colors.white,
decoration: TextDecoration.underline),
border: OutlineInputBorder(
borderRadius: BorderRadius.all(Radius.circular(12))),
),
),
InkWell(
onTap: () => _quizStarted(),
child: Container(
width: double.infinity,
alignment: Alignment.center,
padding: EdgeInsets.all(15),
decoration: BoxDecoration(
borderRadius: BorderRadius.all(Radius.circular(20)),
gradient: (LinearGradient(
colors: [Colors.lime, Colors.blueGrey.shade700],
begin: Alignment.topRight,
end: Alignment.bottomLeft))),
child: Text('START THE APPLICATION',
style: Theme.of(context)
.textTheme
.button
?.copyWith(color: Colors.white38)),
),
),
Spacer(),
],
),
))
],
),
);
}
}
but when I used the same code in another section(the one below) the error "Failed assertion: line 1927 pos 12: 'hasSize'" appears
**import 'package:flutter/material.dart';
class Answer extends StatelessWidget {
final VoidCallback ansk;
final String gimme_Da_Answer;
Answer(this.ansk, this.gimme_Da_Answer);
#override
Widget build(BuildContext context) {
return Stack(
alignment: AlignmentDirectional.bottomCenter,
children: [
SizedBox.expand(
// -> 01
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: NetworkImage(
'https://wallpapercave.com/wp/wp5561184.jpg'),
fit: BoxFit.fitHeight, // -> 02
),
),
),
),
SafeArea(
child: Padding(
padding: const EdgeInsets.symmetric(vertical: 18, horizontal: 17),
child: InkWell(
onTap: () => ansk(),
child: (Container(
child: Text(gimme_Da_Answer,textAlign: TextAlign.center,
style: TextStyle(
fontSize: 25,
color: Colors.cyan.shade800,
fontWeight: FontWeight.bold)),
width: double.infinity,
padding: EdgeInsets.all(15),
margin: EdgeInsets.all(10),
decoration: BoxDecoration(
border: Border.all(color: Colors.blue, width: 4),
color: Colors.blueAccent.shade100.withOpacity(0.4),
borderRadius: BorderRadius.all(Radius.circular(15))),
)),
),
),
),
]);
}
}**
^the code that shows error for me
THANKS A LOT!!!

Answer 1

The error occurs here because the Widget is looking for a size since fit has been set on the BoxDecoration. To solve this issue, set a width and height on the Container.
Container(
// set Container dimension
width: 100,
height: 100,
decoration: BoxDecoration(
image: DecorationImage(
image: NetworkImage(),
fit: BoxFit.cover,
),
),
)