flutter CachedNetworkImage 无法按预期工作

Question

我正在尝试使用缓存的图像。我跟着这个https://flutter.dev/docs/cookbook/images/cached-images ,但它不起作用。

CachedNetworkImage 抛出错误:“无法将参数类型‘CircularProgressIndicator’分配给参数类型‘(BuildContext, String) → Widget’。(argument_type_not_assignable at [hello2] lib/main.dart:21)”

下面是问题代码:

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

重新安装你的应用程序然后再次运行就可以了，它对我有用

    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',
          ),
        ),
      ),
    );
  }
}