使用提供程序实例化列表

Question

我正在努力学习如何使用ChangeNotificationProvider，但遇到了困难。我已经这样设置了类：

void main() => runApp(
ChangeNotifierProvider(create: (context) => ItemList(),
child: MyApp(),
)
);
class ItemData {
final String title;
final int score;
ItemData({required this.title, required this.score});
}
class ItemList extends ChangeNotifier{
final _items = [];
void add(item){
_items.add(item);
notifyListeners();
}
void update(){
notifyListeners();
}
}
final itemList = ItemList();

现在我想创建列表：

我正在尝试通过调用添加项目

itemList.add(ItemData({elements}))

但这不起作用。如何创建列表以便将其放入Listview Builder？

Answer 1

试试这个：

main.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() => runApp(
const MyApp(),
);
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: ChangeNotifierProvider(
create: (context) => ItemList(), child: const NewHomePage()),
);
}
}
class NewHomePage extends StatefulWidget {
const NewHomePage({Key? key}) : super(key: key);
@override
_NewHomePageState createState() => _NewHomePageState();
}
class _NewHomePageState extends State<NewHomePage> {
@override
Widget build(BuildContext context) {
return Consumer<ItemList>(builder: (context, providerItem, child) {
return Scaffold(
appBar: AppBar(
backgroundColor: const Color(0XFF2e3438),
),
body: Column(
mainAxisSize: MainAxisSize.min,
children: [
providerItem.basketItem.isEmpty
? const Text("No item in the list")
: ListView.builder(
itemCount: providerItem.basketItem.length,
shrinkWrap: true,
itemBuilder: (context, index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
"Title: " + providerItem.basketItem[index].title),
);
}),
ElevatedButton(
onPressed: () {
providerItem.addItem(ItemData(
title: DateTime.now().toString(),
score: DateTime.now().month));
print("data added successfully" +
providerItem.basketItem.length.toString());
},
child: const Text("Add Data")),
],
));
});
}
}

item_data.dart

class ItemData {
final String title;
final int score;
ItemData({required this.title, required this.score});
}

item_list.dart

class ItemList extends ChangeNotifier {
List<ItemData> _items = [];
void addItem(ItemData itemData) {
_items.add(itemData);
notifyListeners();
}
List<ItemData> get basketItem {
return _items;
}
}