listview - 如何通过ListView.Custom类型创建ListView

Question

如何通过 ListView.Custom 创建 ListView 。我尝试使用 ListView.Builder 和 ListView.Separted。两者都工作正常。

import 'package:flutter/material.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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          // Here we take the value from the MyHomePage object that was created by
          // the App.build method, and use it to set our appbar title.
          title: Text(widget.title),
        ),
        body: ListView.custom(
          scrollDirection: Axis.vertical,
          reverse: false,
          childrenDelegate: new MyCustomDelegate(),));
  }
}

List<String> listItems = ["One", "Two", "Three", "Four","Five","Six"];


class MyCustomDelegate extends SliverChildDelegate {

 @override
   int get estimatedChildCount => listItems.length;  

  @override
    bool shouldRebuild(SliverChildDelegate oldDelegate) {
      return true;
    }
  @override
    Widget build(BuildContext context, int index) {
      return Container(padding: new EdgeInsets.only(top: 16.0),
      child: new Text(listItems[index]),);

    }
}

谁能帮我解决这个问题。提前致谢。

Answer 1

您应该添加验证以确保您的项目在范围内:

     @override
    Widget build(BuildContext context, int index) {
      return index < estimatedChildCount
          ? Container(
              padding: new EdgeInsets.only(top: 16.0),
              child: new Text(listItems[index]),
            )
          : null;
    }