颤振/飞镖 当我尝试从互联网导入数据时，它不会加载它

Question

我是Flutter/Dart的新手... 我正在尝试使用 json.decode 从 http 导入数据，但它始终为空，显示"正在加载..."。我正在使用FutureBuilder！我已经搜索了解决方案，但没有找到。我正在使用 https://jsonplaceholder.typicode.com/posts 来模拟它。 希望有人能帮忙！:))

class Page1 extends StatelessWidget {
//********************************** GOOGLE MAPS *****************************************
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: MapView(),
);
}
}
class MapView extends StatefulWidget {
@override
_MapViewState createState() => _MapViewState();
}
class _MapViewState extends State<MapView> {
CameraPosition _initialLocation = CameraPosition(target: LatLng(0.0, 0.0));
GoogleMapController mapController;
final Geolocator _geolocator = Geolocator();
Position _currentPosition;
@override
void initState() {
super.initState();
_getCurrentLocation();
}
_getCurrentLocation() async {
await _geolocator
.getCurrentPosition(desiredAccuracy: LocationAccuracy.high)
.then((Position position) async {
setState(() {
// Store the position in the variable
_currentPosition = position;
print('CURRENT POS: $_currentPosition');
// For moving the camera to current location
mapController.animateCamera(
CameraUpdate.newCameraPosition(
CameraPosition(
target: LatLng(position.latitude, position.longitude),
zoom: 13.0,
),
),
);
});
}).catchError((e) {
print(e);
});
}
@override
Widget build(BuildContext context) {
// Determining the screen width & height
var height = MediaQuery.of(context).size.height;
var width = MediaQuery.of(context).size.width;

//********************************** GOOGLE MAPS SCREEN **********************************
return Container(
height: height,
width: width,
child: Scaffold(
body: Stack(
children: <Widget>[
GoogleMap(
initialCameraPosition: _initialLocation,
myLocationEnabled: true,
myLocationButtonEnabled: false,
mapType: MapType.normal,
zoomGesturesEnabled: true,
zoomControlsEnabled: false,
onMapCreated: (GoogleMapController controller) {
mapController = controller;
},
),
SafeArea(child:
Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Container(
child: Material(
shape:StadiumBorder(),
color: Color(0xffeb5c68),
child: InkWell(
splashColor: Color(0xffda1b2b) ,
child: SizedBox(
width: 130,
height: 47,
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text("MY ORDERS", style: TextStyle(fontWeight: FontWeight.bold)),
SizedBox(width: 3),
Icon(Icons.arrow_forward),
]
),
),
onTap: () {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Page2()),
);
},
),
),
)
]
),
),
SafeArea(child:
Row(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
ClipOval(
child: Material(
color: Color(0xffeb5c68),
child: InkWell(
splashColor: Color(0xffda1b2b),
child: SizedBox(
width: 56,
height: 56,
child: Icon(Icons.my_location, size: 28,),
),
onTap: () {
mapController.animateCamera(
CameraUpdate.newCameraPosition(
CameraPosition(
target: LatLng(
_currentPosition.latitude,
_currentPosition.longitude,
),
zoom: 13.0,
),
),
);
},
),
),
),
]
),
),
//********************************** ORDERS **********************************
Container(
padding: EdgeInsets.only(top: 550, bottom: 50),
child: FutureBuilder(
future: getTechies(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
print(snapshot.data);
if (snapshot.data == null) {
return Container(
child: Center(
child: Text("Loading...", style: TextStyle(fontSize: 30),)
)
);
} else {
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (BuildContext context, int index){
return ListTile(
title: Text(snapshot.data[index].userId),
subtitle: Text(snapshot.data[index].id),
);
}
);
}
}
)
),
],
)
),
);
}
Future<List<Technician>> getTechies() async {
var data = await http.get("https://jsonplaceholder.typicode.com/posts");
var jsonData = json.decode(data.body);
List<Technician> techies = [];
for (var u in jsonData) {
Technician myTechy = Technician(u["userId"], u["id"], u["tittle"], u["body"]);
techies.add(myTechy);
}

return techies;
}
}
//********************************** PAGE 2 **********************************
class Page2 extends StatelessWidget {

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("YOUR ORDERS"),
backgroundColor: Colors.green
),
);
}
}

技术员类：

class Technician {
final String userId;
final String id;
final String tittle;
final String body;

Technician(this.userId, this.id, this.tittle, this.body);
}

Answer 1

处理数据时出错。

使用尝试捕获查看错误。您将看到此错误

类型">

int"不是类型"字符串"的子类型

这是解决方法

Future<List<Technician>> getTechies() async {
try {
var data = await http.get("https://jsonplaceholder.typicode.com/posts");
var jsonData = json.decode(data.body);
List<Technician> techies = [];
for (var u in jsonData) {
Technician myTechy = Technician(u["userId"], u["id"], u["tittle"], u["body"]);
techies.add(myTechy);
}
return techies;
} catch (e) {
print(e);
}
}

id和userIdint.所以把你的Technician类改成这个

class Technician {
final int userId;
final int id;
final String tittle;
final String body;
Technician(this.userId, this.id, this.tittle, this.body);
}

如果您不想更改Technician类。在循环中执行此操作

for (var u in jsonData) {
Technician myTechy = Technician(u["userId"].toString(), u["id"].toString(), u["tittle"], u["body"]);
techies.add(myTechy);
}

然后将您的列表生成器更改为此

return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (BuildContext context, int index) {
return ListTile(
title: Text(snapshot.data[index].userId.toString()),
subtitle: Text(snapshot.data[index].id.toString()),
);
},
);