问使用CachedNetworkImage动态改变图像的ListView

EN

import 'package:flutter/material.dart';
import 'package:cached_network_image/cached_network_image.dart';

void main() => runApp(new MyApp());

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return new MyAppState();
  }
}

class MyAppState extends State<MyApp> {
  double padding = 5.0;

  String one = 'https://SOME_URL_HERE.com';
  String two = 'https://SOME_URL_HERE.com';
  String three = 'https://SOME_URL_HERE.com';
  String four = 'https://SOME_URL_HERE.com';
  List urls;

  @override
  Widget build(BuildContext context) {
    urls = List();
    urls.add(one);
    urls.add(two);

    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text("Image list test"),
        ),
        body: showBody(),
      ),
    );
  }

  Widget showBody() {
    return Padding(
      padding: EdgeInsets.only(top: 15.0, left: 10.0, right: 10.0),
      child: ListView(
        children: <Widget>[
          showItemImages(),
          RaisedButton(
            child: Text("Change image"),
            onPressed: () {
              setState(() {
                urls = List();
                urls.add(three);
                urls.add(four);
              });
            },
          ),
          Container(
            child: Text('urls length: ${urls.length}'),
          ),
        ],
      ),
    );
  }

  Widget showItemImages() {
    return Padding(
      padding: EdgeInsets.all(padding),
      child: Container(
          margin: EdgeInsets.symmetric(vertical: 20.0),
          height: 200,
          child: urls.length > 0 //item.images.length > 0
              ? getImagesListView(context)
              : Container(child: Text('No images yet'))),
    );
  }

  getImagesListView(BuildContext context) {
    return ListView.builder(
      shrinkWrap: true,
      scrollDirection: Axis.horizontal,
      itemCount: urls.length,
      itemBuilder: (BuildContext context, int index) {
        return new Container(
          width: 160.0,
          child: _sizedContainer(
            new CachedNetworkImage(
              key: new ValueKey<String>(urls[index]),
              imageUrl: urls[index],
              //placeholder: (context, url) => new CircularProgressIndicator(),
            ),
          ),
        );
      },
    );
  }

  Widget _sizedContainer(Widget child) {
    return new SizedBox(
      width: 300.0,
      height: 150.0,
      child: new Center(
        child: child,
      ),
    );
  }
}