理解编程作为一个初学者，在扑，是我的编码错误或有问题，我的连接即没有有效的SSL证书?

Question

import 'package:flutter/material.dart';
import 'package:http/http.dart' as https;
import 'dart:convert';
//above is for import
class Loading extends StatefulWidget {
const Loading({Key? key}) : super(key: key);
@override
State<Loading> createState() => _LoadingState(); //code here
} //code above
//below code
class _LoadingState extends State<Loading> {
void getTime () async {
//make the request for timezone from Europe,London
Uri url = Uri.parse('https://worldtimeapi.org/api/timezone/Europe/London');
https.Response response = await https.get(url);
Map data = jsonDecode(response.body);
// print(data);
//code above
//get properties from data
String datetime = ['datetime'] as String;
String offset = ['offset'] as String;
print(datetime);
print(offset);
}
@override
void initState() {
super.initState();
getTime();
//code above
}

@override
Widget build(BuildContext context) {
return Scaffold(
body: Text('loading screen'),
);
}
}

下面是我的控制台:

Performing hot restart...
Syncing files to device AOSP on IA Emulator...
Restarted application in 1,541ms.
E/flutter (16861): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'List<String>' is not a subtype of type 'String' in type cast
E/flutter (16861): #0      _LoadingState.getTime (package:world_time/pages/loading.dart:22:36)
E/flutter (16861): <asynchronous suspension>
E/flutter (16861): 

Answer 1

问题在这里:

String datetime = ['datetime'] as String;
String offset = ['offset'] as String;

您正在将List<String>([""])分配给String。

{
"abbreviation": "BST",
"client_ip": "223.225.60.61",
"datetime": "2023-04-12T08:34:34.157770+01:00",
"day_of_week": 3,
"day_of_year": 102,
"dst": true,
"dst_from": "2023-03-26T01:00:00+00:00",
"dst_offset": 3600,
"dst_until": "2023-10-29T01:00:00+00:00",
"raw_offset": 0,
"timezone": "Europe/London",
"unixtime": 1681284874,
"utc_datetime": "2023-04-12T07:34:34.157770+00:00",
"utc_offset": "+01:00",
"week_number": 15
}

也没有名为"offset"在JSON响应中。所以，做这些修改:

String datetime = data['datetime'];
String offset = data['dst_offset'];