在 app 开发中，最重要的部分是，我们需要从服务或者本地获取数据，渲染到我们的挂件中。
整体效果 Gif 图：
下面，我们按照步骤来在 ListView 挂件中使用 JSON 文件：
第 1 步：创建一个 Flutter 项目
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',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primaryColor: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget{
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Listview using local json file'),
),
body: Center(),
);
}
}
第 2 步：插入 ListView 挂件
body: Center(
child: ListView.builder(
itemBuilder: (BuildContext context, int index) {
return Card(
child: Padding(
padding: const EdgeInsets.only(
top: 32,
bottom: 32,
left: 16,
right: 16,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
InkWell(
onTap: () {},
child: Text(
'Country',
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 22,
),
),
),
Text(
'Capital',
style: TextStyle(
color: Colors.grey.shade600,
),
)
],
),
Container(
height: 50,
width: 50,
child: Image.asset('assets/images/face1.jpg'),
),
],
),
),
);
}
itemCount: 5,
),
),
第 3 步：在 assets 文件夹中创建 JSON 文件
[
{
"title": "Yogita",
"text": "Kumar",
"img": "assets/images/face1.jpeg"
},
{
"title": "Abhishek",
"text": "Kumar",
"img": "assets/images/face1.jpeg"
},
{
"title": "Shashwat Kumar",
"text": "Singh",
"img": "assets/images/face1.jpeg"
},
{
"title": "Advika",
"text": "Singh",
"img": "assets/images/face1.jpeg"
},
{
"title": "Yamini",
"text": "Gupta",
"img": "assets/images/face1.jpeg"
},
{
"title": "Nisha",
"text": "Rawal",
"img": "assets/images/face1.jpeg"
},
{
"title": "Bhavesh",
"text": "Joshi",
"img": "assets/images/face1.jpeg"
},
{
"title": "Rahul",
"text": "Khanna",
"img": "assets/images/face1.jpeg"
}
]
编辑 pubspec.yaml 文件：
# To add assets to your application, add an assets section, like this:图片资源
第 4 步：从 details.json 文件中解码并获取数据
先导入 dart:convert。
import 'dart:convert';
然后声明类型为 List 的变量。
List将下面的代码添加上去：
FutureBuilder(
future: DefaultAssetBundle.of(context)
.loadString('assets/loadjson/details.json'),
builder: (context, snapshot) {
// Decode the JSON
FutureBuilder：一旦从未来返回结果，就会构建小挂件。
future：此参数接收结果并将结果发送到 Builder。
builder：此参数接收来自 feature 的数据并返回给小挂件。可以在此处对接接收到的数据并执行任何操作。
initialData：可选的参数，如果我们设置 initialData 参数的值，builder 将会在 future 返回数据前展示 initialData。
这里的 loadString() 函数是用来获取本地 JSON 文件。
future 参数接收到函数返回来的数据之后，将数据传递给 futureBuilder 参数。
builder 解析字符串并返回生成的 Json 对象。
第 5 步：将获取的 JSON 文件的数据写入 ListView 挂件中
return ListView.builder(
itemBuilder: (BuildContext context, int index) {
return Card(
child: Padding(
padding: const EdgeInsets.only(
top: 32,
bottom: 32,
left: 16,
right: 16,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (_) => Welcome()),
);
},
child: Text(
data[index]['title'],
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 22,
),
),
),
Text(
data[index]['text'],
style: TextStyle(
color: Colors.grey.shade600,
),
)
],
),
Container(
height: 50,
width: 50,
child: Image.asset(data[index]['img']),
),
],
),
),
);
},
itemCount: data == null ? 0
itemCount 允许我们在 ListView 挂件中显示所需的条数。
最终的程序 main.dart：
import 'package:flutter/material.dart';
import 'dart:convert';
import 'welcome.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget{
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primaryColor: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget{
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List data = [];
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('ListView using local json file'),
),
body: Center(
child: FutureBuilder(
future: DefaultAssetBundle.of(context)
.loadString('assets/loadjson/details.json'),
builder: (context, snapshot) {
data = json.decode(snapshot.data.toString());
return ListView.builder(
itemBuilder: (BuildContext context, int index) {
return Card(
child: Padding(
padding: const EdgeInsets.only(
top: 32,
bottom: 32,
left: 16,
right: 16,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (_) => Welcome()),
);
},
child: Text(
data[index]['title'],
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 22,
),
),
),
Text(
data[index]['text'],
style: TextStyle(
color: Colors.grey.shade600,
),
)
],
),
Container(
height: 50,
width: 50,
child: Image.asset(data[index]['img']),
),
],
),
),
);
},
itemCount: data == null ? 0
输出:
welcome.dart 文件资源：
import 'package:flutter/material.dart';
class Welcome extends StatefulWidget{
@override
_WelcomeState createState() => _WelcomeState();
}
class _WelcomeState extends State<Welcome> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Welcome'),
),
body: Center(
child: Text(
"You are Welcome",
style: TextStyle(
fontSize: 25,
fontWeight: FontWeight.bold,
),
),
),
);
}
}
显示效果：
