如何在创建UI之前调用API,并且仅当API响应出现波动时才加载UI。
[基本上,我只想在API响应到来时才加载UI,否则我想显示错误消息,那么有人可以帮我吗?如何做到这一点?
使用FutureBuilder
:
基于交互的最新快照自行构建的小部件与未来。
完整示例:
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
// podo class
class ObjectClass {
String name;
ObjectClass({this.name});
ObjectClass.fromJson(Map<String, dynamic> json) {
name = json['name'];
}
}
class Demo extends StatefulWidget {
@override
_DemoState createState() => new _DemoState();
}
class _DemoState extends State<Demo> {
Future<List<ObjectClass>> fetchJson() async {
final response = await http.Client().get('your json url');
return compute(parseJson, response.body);
}
// A function that converts a response body into a List<ObjectClass>.
List<ObjectClass> parseJson(String responseBody) {
final parsed = json.decode(responseBody).cast<Map<String, dynamic>>();
return parsed
.map<ObjectClass>((json) => ObjectClass.fromJson(json))
.toList();
}
Widget _bodyBuild({List<ObjectClass> data}) {
return Container(); // make your ui here and use the 'data' variable
}
Widget demoBody() {
return FutureBuilder<List<ObjectClass>>(
future: fetchJson(), // api call method here, to fetch json/data
builder: (context, snapshot) {
if (snapshot.hasError) {
return Container(); // widget to be shown on any error
}
return snapshot.hasData
? _bodyBuild(data: snapshot.data)
: Text("Loading"); // widget to be shown while data is being loaded from api call method
},
);
}
@override
Widget build(BuildContext context) {
return Scaffold(appBar: AppBar(title: Text("DEMO")), body: demoBody());
}
}