flutter CachedNetworkImage doesn't work as expected - flutter

Question

I'm trying to work with cached images.
I followed this https://flutter.dev/docs/cookbook/images/cached-images,
but it doesn't work.
CachedNetworkImage throws error: "The argument type 'CircularProgressIndicator' can't be assigned to the parameter type '(BuildContext, String) → Widget'. (argument_type_not_assignable at [hello2] lib/main.dart:21)"
Below is the problem code:
import 'package:flutter/material.dart';
import 'package:cached_network_image/cached_network_image.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
final title = 'Cached Images';
return MaterialApp(
title: title,
home: Scaffold(
appBar: AppBar(
title: Text(title),
),
body: Center(
child: CachedNetworkImage(
placeholder: CircularProgressIndicator(),
imageUrl:
'https://picsum.photos/250?image=9',
),
),
),
);
}
}
```dart

Answer 1

reinstall your application and then run again will work, it worked for me
import 'package:flutter/material.dart';
import 'package:cached_network_image/cached_network_image.dart';
class App extends StatelessWidget {
const App({Key key}) : super(key: key);
#override
Widget build(BuildContext context) {
final title = 'Cached Images';
return MaterialApp(
title: title,
home: Scaffold(
appBar: AppBar(
title: Text(title),
),
body: Center(
child: CachedNetworkImage(
placeholder: (context, url) => CircularProgressIndicator(),
imageUrl: 'https://picsum.photos/250?image=9',
),
),
),
);
}
}

Answer 2

It works after changing:
placeholder: CircularProgressIndicator(),
to:
placeholder: (context, url) => new CircularProgressIndicator(),
BTW: cached_network_image had a breaking change in 0.6.0.
The tutorial link (https://flutter.dev/docs/cookbook/images/cached-images) is out of date.

Answer 3

I would like to add explanation to the above agreed answer.
placeholder is of type Widget Function(BuildContext, String)? placeholder
So it throws you error:
The argument type CircularProgressIndicator can't be assigned to the parameter type (BuildContext, String) → Widget
Convert:
placeholder: CircularProgressIndicator()
to
placeholder: (context, url) => new CircularProgressIndicator(),