I have the following code which should show a process indicator during the process of fetching a JSON data from the web. It works fine when I run in the debug mode. But as soon as I make it to an apk, the app opens and with no time delays, it throws this error:
SocketException:
How to get rid of these issues?
import 'package:flutter/material.dart';
import 'dart:async';
import 'package:http/http.dart' as http;
import 'dart:convert' as convert;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Quize It Up'),
);
}
}
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
void initState() {
super.initState();
getCategories();
}
Future<List> getCategories() async {
var url = 'https://opentdb.com/api_category.php';
var response = await http
.get(Uri.encodeFull(url), headers: {"Accept": "application/json"});
var jsonResponse = convert.jsonDecode(response.body);
List categories = jsonResponse["trivia_categories"];
return categories;
}
Widget mainGui() {
return Container(
child: FutureBuilder(
future: getCategories(),
builder: (BuildContext context, AsyncSnapshot<List> asyncSnapshot) {
switch (asyncSnapshot.connectionState) {
case ConnectionState.active:
case ConnectionState.waiting:
return Center(
child: CircularProgressIndicator(),
);
case ConnectionState.none:
return RaisedButton(
onPressed: () => getCategories(),
);
case ConnectionState.done:
if (asyncSnapshot.hasData)
return Text(asyncSnapshot.error.toString());
else
return ListView.builder(
itemCount: asyncSnapshot.data.length,
itemBuilder: (context, int index) {
return ListTile(
title: Text(asyncSnapshot.data[index]['name']),
);
},
);
}
}));
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Container(
child: mainGui(),
),
);
}
}
First of all you are calling getCategories();
in your initState()
method for no reason. Since getCategories()
is simply building and returning a Future that you don't use in initState this call is irrelevant. You might simply delete this line or even the entire initState()
method.
Then this code basically does nothing:
case ConnectionState.none:
return RaisedButton(
onPressed: () => getCategories(),
);
In order to show a button that reloads the Future you might instead refresh the state like this. This will rebuild your widget and therefore rebuild the future.
case ConnectionState.none:
return RaisedButton(
onPressed: () {
setState(() {});
},
);
But anyways. If all that you want to achieve is a loading indicator while the Future is loading I'd rather observe the hasData
attribute of the snapshot. Something like this might work:
return FutureBuilder (
future: getCategories(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.hasData) {
if (snapshot.data) {
return ListView.builder(
itemCount: asyncSnapshot.data.length,
itemBuilder: (context, int index) {
return ListTile(
title: Text(asyncSnapshot.data[index]['name']),
);
},
);
}
} else {
return Center(
child: CircularProgressIndicator(),
);
}
}
);
Just for clarity. The error you are seeing is coming from this bug here:
case ConnectionState.done:
if (asyncSnapshot.hasData)
return Text(asyncSnapshot.error.toString());
Your saying here that if the Future is done and has some data received then you show the error instead of the data.
The solution was to add<uses-permission android:name="android.permission.INTERNET"/>
in the manifest.xml file as the latest flutter SDK has changed the project structure.
是的,解决方案是添加<uses-permission android:name="android.permission.INTERNET"/>
,但您必须将其添加到 Flutter 项目中 /android/src/main 位置的 AndroidManifest.xml 文件中
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