解析未来生成器时出错： 类型错误： 无法读取 null 的属性'Symbol(dartx._get)'

Question

我正在调用一个未来的生成器生成器，并得到以下错误："TypeError：无法读取null的属性"Symbol(dartx.get("；即使我正在获取json数据。未来构建器打印当我调用json时，我得到错误：NoSoke方法错误：屏幕上null上的无效成员：'get'，但我不知道哪里出了问题。

EDIT 1:userEvents是一个类级变量，可在的任何位置访问

这是我的未来：

FutureBuilder(
future: getMyEvents(),
builder: (context, snapshot) {
if (snapshot.hasError) {
return Text('Error: ${snapshot.error}');
} else {
switch (snapshot.connectionState) {
case ConnectionState.done:
_events = snapshot.data;
print("received my event data");
print(snapshot.data);
return _eventData();
break;
case ConnectionState.waiting:
CircularProgressIndicator();
break;
default:
}
}
return snapshot.data != null
? _eventData()
: _noEvents();
}),

我的api：

Future getMyEvents() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
var token = prefs.getString('token');
print('my token is $token');
var events;
final Map<String, dynamic> body = {
'access_token': token,
};
var url = "$server/api/events/my_events/";
await http.post(url, body: body, headers: {
"Content-Type": "application/x-www-form-urlencoded"
}).then((http.Response response) {
print(response.body);
var responseData = json.decode(response.body);
switch (response.statusCode) {
case (200):
UserEvents userEvents = UserEvents.fromJson(responseData);
print('My Events ${userEvents.events[0]}');
events = userEvents.events;
print('Events received');
print('Events ${events}');
break;
case (500):
print('No Events In This City');
return '';
break;
}
});
return userEvents;
}

这是打印在响应正文中的JSON数据：

{
"success": [
{
"id": 1,
"event_name": "Test Event 1",
"event_photo": "https://dispensaries.s3.amazonaws.com/event_photo/91dfce63-5f52-4e7e-bb38-a5a2800631cc_preview_gD0YH8V.png",
"vendor_name": {
"id": 1,
"vendor": "Test Vendor 1"
},
"refund_available": true,
"website": "www.test.com",
"share_count": 0,
"check_in_count": 1,
"street_address": "1231 faker streat",
"city": "Jersey City",
"state": "NJ",
"zipcode": "01010",
"event_tagline": "test",
"details": "test",
"start_date": "2020-11-27",
"start_time": "22:44:00",
"end_time": "22:44:00",
"attendees": [
{
"id": 2,
"name": "test user",
"current_selfie": "https://dispensaries.s3.amazonaws.com/sefies/cbdYoga.jpeg"
}
]
},

]
}

我该怎么解决这个问题？

Answer 1

因为userEvents变量是在switch语句内部定义的，所以在该范围之外是未定义的。将定义移动到块外，或者直接从情况返回:

switch (response.statusCode) {
case (200):
UserEvents userEvents = UserEvents.fromJson(responseData);
print('My Events ${userEvents.events[0]}');
events = userEvents.events;
print('Events received');
print('Events ${events}');
return userEvents;
// ...
}