另一個類別中呼叫時，Flutter無法取得變數的新值
我有這個 StatefulWidget，它應該根據條件從 MySQL 資料庫檢索資料並將這些檢索到的值添加到數組中，以便我可以使用數組值顯示在 ListView 上。我的問題是，有時當陣列 (_fileValues) 和 _custUsername 變數為空或未更新時，不會引發例外狀況。
這是我的有狀態小工具 (main.dart)
String? _custUsername;
List<String> _fileValues = <String>[];
class cakeLogin extends StatefulWidget {
@override
cakeLoginPageMain createState() => cakeLoginPageMain();
}
class cakeLoginPageMain extends State<cakeLogin> {
String? _CustEmailInit;
BuildContext? loginContext;
List<String> _fileNameStores = <String>[];
void callData() {
// @ Get username based on user email and assign it to _custUsername variable
UsernameGetter().Connection(_CustEmailInit!).then((UsernameValue) {
_custUsername = UsernameValue!;
});
// @ Get item names based on the user username (_custUsername) and add them into
// _fileNameStores
NameGetter().Connection(_custUsername).then((NamesValues) {
for(var _nameItems in NamesValues) {
setState(() {
_fileNameStores.add(_nameItems);
});
}
});
// @ Remove duplicates value and add them into main list (_fileValues)
var _removeDuplicates = _fileNameStores.toSet().toList();
for(var item in _removeNamesDupes) {
setState(() {
_fileValues.add(item);
});
}
}
@override
Widget build(BuildContext context) {
final _emailController = TextEditingController();
return Scaffold(
appBar: AppBar(
title: Text("Login to App",
style: TextStyle(
fontSize: 18,
color: setupFontCol,
fontWeight: FontWeight.bold
)),
backgroundColor: setupThemeBar,
centerTitle: true,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(20),
)
),
backgroundColor: setupMainTheme,
body: Padding(
padding: EdgeInsets.all(20),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
TextFormField(
controller: _emailController,
style: TextStyle(color: Color.fromARGB(255, 214, 213, 213)),
decoration: InputDecoration(
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
filled: true,
hintStyle: TextStyle(color: Color.fromARGB(255, 197, 197, 197)),
hintText: "Enter your email",
fillColor: setupThemeBar
),
),
SizedBox(height: 18),
SizedBox(height: 25),
SizedBox(
height: 45,
width: 500,
child: ElevatedButton(
style:
ElevatedButton.styleFrom(
primary: setupFontCol,
onPrimary: Colors.white,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10),
)
),
onPressed: () {
var _CustEmail = _emailController.text;
if(_CustEmail.contains("@gmail.com") || _CustEmail.contains("@email.com")) {
if(_CustEmail != "") {
_CustEmailInit = _CustEmail;
loginContext = context;
_isFromLogin = true;
_fileValues.clear();
callData();
} else {
alertDialog("Please enter your email address",context);
}
} else {
alertDialog("Email address is not valid",context);
}
},
//color: setupFontCol,
child: Text("Login",
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.normal,
fontSize: 14,
))
),
),
],
),
),
);
}
}
UsernameGetter 類別（此類將根據文字欄位輸入中的電子郵件從資料庫表中檢索使用者使用者名稱）
當我從UsernameGetter 類別列印_usernameDetected 類別時，它會傳回傳回字串的更新版本，但是當我將_custUsername# 指派給 UsernameValue 從main.dart 時，它不會更新，有時會傳回null值。
import 'package:mysql_client/mysql_client.dart';
import 'dart:convert';
import 'dart:ffi';
import 'dart:typed_data';
import 'package:signuppage/main.dart' as main;
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
class UsernameGetter {
Future<String> Connection(String _custEmail) async {
final conn = await MySQLConnection.createConnection(
host: "",
port: ,
userName: "",
password: "",
databaseName: "",
);
await conn.connect();
var _getUsernameQue = await conn.execute("SELECT CUST_USERNAME FROM information WHERE CUST_EMAIL = :email",
{
"email": _custEmail
});
String? _usernameDetected;
for(final _rowsOfEmail in _getUsernameQue.rows) {
_usernameDetected = _rowsOfEmail.assoc()['CUST_USERNAME']!;
}
return await _usernameDetected!;
}
}
NameGetter 類別（檢索儲存在文字列中的使用者項目名稱）
對於 NameGetter 類，與 UsernameGetter 發生相同的情況。當我從 main.dart 檢索值並將值加到 _fileValues 列表中時，有時該值為空，有時該值未更新。
import 'package:mysql_client/mysql_client.dart';
import 'dart:convert';
import 'dart:ffi';
import 'dart:typed_data';
import 'package:signuppage/main.dart' as main;
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
class NameGetter {
Future<List<String>> Connection(String _custUsername) async {
final conn = await MySQLConnection.createConnection(
host: "",
port: ,
userName: "",
password: "",
databaseName: "",
);
await conn.connect();
var _getItemNames= await conn.execute("SELECT ITEM_NAMES FROM item_details WHERE CUST_USERNAME = :username",
{
"username": _custUsername
});
List<String>? _itemNamesValues= <String>[];
for(var _rowsOfItemNames in _getItemNames.rows) {
var _retrieveNames = await _rowsOfItemNames.assoc()['ITEM_NAMES']!;
_itemNamesValues.add(_retrieveNames);
}
return await _itemNamesValues;
}
}
我不確定我的錯誤在哪裡，但我很確定我犯了很多錯誤，我需要有人幫我解決。特別是關於為什麼列表和變數沒有更新/有時是空的。
參考連結：
Flutter ListView 未更新
我在 flutter 中的列表沒有更新程式碼中的問題
為什麼變數值在flutter中不刷新？
