android - ListView 无限构建项目

Question

我写了一个 Flutter ListView 演示，我希望 ListView 自动滚动到最后一张图片，然后返回到第一个，对于我放的演示2 张图片，调试时一切正常，ListView 显示无限项。但是，当涉及到发布版本时，它会无限地构建项目。

如其所示，它确实适用于调试。

import 'dart:ui';

import 'package:flutter/material.dart';
import 'package:flutter_demo_module/screenutil.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      theme: ThemeData(
        primaryColor: Colors.white,
      ),
      home: _InfiniteGallery(),
    );
  }
}

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

class _InfiniteGalleryState extends State<_InfiniteGallery> {
  ListView list;
  ScrollController _controller;
  List<Image> cache = List();

  Widget _buildItem(index) {
    print("build item $index");
    final imageIndex = index % 2;
    if (cache.length <= imageIndex) {
      Image image = Image.asset(
        'images/welcome_banner_$imageIndex.jpg',
        height: ScreenUtil.getInstance().setWidth(367),
        width: ScreenUtil.getInstance().setWidth(305),
      );
      cache.add(image);
    }
    return cache[imageIndex];
  }

  Widget _buildSuggestions() {
    list = ListView.builder(
      controller: _controller,
      shrinkWrap: true,
      scrollDirection: Axis.horizontal,
      padding: const EdgeInsets.all(0),
      itemBuilder: (context, i) {
        return _buildItem(index);
      },
    );
    return list;
  }

  @override
  Widget build(BuildContext context) {
    ScreenUtil(width: 375).init(context);
    final titleStyle = TextStyle(
      fontSize: 14.0,
      color: Colors.deepOrangeAccent,
    );
    return Scaffold(
      appBar: AppBar(
        brightness: Brightness.light,
        title: Text(
          "Startup Name Generator11",
          style: titleStyle,
        ),
        actions: <Widget>[
          new IconButton(icon: const Icon(Icons.library_add), onPressed: null),
        ],
      ),
      body: Column(
        children: <Widget>[
          Container(
            height: ScreenUtil.getInstance().setWidth(367),
            child: _buildSuggestions(),
          ),
        ],
      ),
    );
  }
}

这是发布日志:

I/flutter (16705): build item 43693
I/flutter (16705): build item 43694
I/flutter (16705): build item 43695...

Answer 1

添加 itemCount

您没有为 ListView 指定 itemCount，您需要添加一个 itemCount = non-null。

Widget _buildSuggestions() {
list = ListView.builder(
  controller: _controller,
  shrinkWrap: true,
  scrollDirection: Axis.horizontal,
  padding: const EdgeInsets.all(0),

  itemCount: 5,// your count here

  itemBuilder: (context, i) {
    return _buildItem(index);
  },
);
return list;
}