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flutter | Dart - NoSuchMethodError : The method 'map' was called on null

转载 作者:行者123 更新时间:2023-12-03 04:39:20 25 4
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构建时收到错误:
NoSuchMethodError:在 null 上调用了方法“map”。
接收方:空
尝试调用:
map (关闭:交易=>容器)

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building TransactionList(dirty):
The method 'map' was called on null.
Receiver: null
Tried calling: map<Container>(Closure: (Transaction) => Container)

The relevant error-causing widget was:
TransactionList file:///C:/.../AndroidStudioProjects/money_tracker/lib/Widgets/user_transactions.dart:44:9
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
#1 TransactionList.build (package:money_tracker/models/transaction_list.dart:14:30)
#2 StatelessElement.build (package:flutter/src/widgets/framework.dart:4576:28)
#3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4502:15)
#4 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
我相信该错误与 user_transactions.dart 文件中的 TransactionList(_userTransactions) 行有关,但不确定如何解决。
代码:
来自 main.dart:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:gradient_app_bar/gradient_app_bar.dart';
import 'package:money_tracker/Widgets/user_transactions.dart';

void main() {
runApp(Home());
}

class Home extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: GradientAppBar(
centerTitle: true,
gradient: LinearGradient(
colors: [Colors.green, Color(0xff01655e)],
),
title: Text(
'Money Tracker',
style: TextStyle(color: Colors.white),
),
// backgroundColorStart: Color(0xff01655e),
actions: <Widget>[
Icon(Icons.add),
],
),
body: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Container(
width: double.infinity,
margin: EdgeInsets.all(15.0),
child: Card(
//Card is a freestyle container
color: Color(0xff01655e),
child: Text('Chart'),
elevation: 5.0,
),
),
UserTransactions(),
],
),
),
);
}
}
来自 user_transactions.dart:
import 'package:flutter/material.dart';
import 'package:money_tracker/models/transaction_list.dart';
import 'new_transaction.dart';
import '../models/transaction.dart';

class UserTransactions extends StatefulWidget {
@override
_UserTransactionsState createState() => _UserTransactionsState();
}

class _UserTransactionsState extends State<UserTransactions> {
final List<Transaction> _userTransactions = [
Transaction(
id: '1',
title: 'course',
amount: 11.99,
dateTime: DateTime.now(),
),
Transaction(
id: '2',
title: 'milk',
amount: 2.87,
dateTime: DateTime.now(),
),
];

void _addNewTransaction(String txTitle, double amount) {
final newTx = Transaction(
title: txTitle,
amount: amount,
dateTime: DateTime.now(),
id: DateTime.now().toString());

setState(() {
_userTransactions.add(newTx);
});
}

@override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
NewTransaction(_addNewTransaction),
TransactionList(_userTransactions),
],
);
}
}
来自 transaction_list.dart:
import 'package:flutter/material.dart';
import 'transaction.dart';
import 'package:intl/intl.dart';

class TransactionList extends StatelessWidget {
TransactionList(List<Transaction> userTransactions, {this.transactions});
final List<Transaction> transactions;

@override
Widget build(BuildContext context) {
return Column(
children: transactions.map((tx) {
return Container(
margin: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
padding: EdgeInsets.all(0.5),
decoration: BoxDecoration(
border: Border.all(color: Colors.grey, width: 2.0),
borderRadius: BorderRadius.all(
Radius.circular(15.0),
),
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Container(
child: Text(
'\$${tx.amount}',
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 20.0,
),
),
),
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(tx.title,
style: TextStyle(
fontWeight: FontWeight.bold, fontSize: 18.0)),
Text(
DateFormat().format(tx.dateTime),
style: TextStyle(color: Colors.grey),
)
],
),
],
),
);
}).toList(),
);
}
}
来自 transaction.dart:
class Transaction {
Transaction(
{@required this.id,
@required this.title,
@required this.amount,
@required this.dateTime});

final String id;
final String title;
final double amount;
final DateTime dateTime;
}
来自 new_transaction.dart:
class NewTransaction extends StatelessWidget {
final Function addTx;
final title = TextEditingController();
final amount = TextEditingController();

NewTransaction(addNewTransaction, {this.addTx});
@override
Widget build(BuildContext context) {
return Card(
elevation: 5.0,
child: Container(
width: double.infinity,
margin: EdgeInsets.all(15.0),
child: Column(
children: <Widget>[
Text(
'Add New Transaction',
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 20.0,
),
),
TextField(
decoration: InputDecoration(labelText: 'Title'),
controller: title,
// onChanged: (value) {
// title = value;
// },
),
TextField(
decoration: InputDecoration(labelText: 'Amount'),
controller: amount,
// onChanged: (value) {
// amount = value;
// },
),
Padding(
padding: EdgeInsets.all(8.0),
child: FlatButton(
padding: EdgeInsets.all(10.0),
color: Colors.green,
onPressed: () {
addTx(
title.text,
double.parse(amount.text),
);
},
child: Text(
'Add',
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
),
),
),
)
],
),
),
);
}
}

最佳答案

错误表示 transactionsnull .您没有向该参数传递任何内容。
您的 TransactionList构造函数有 2 个参数,但只使用了一个。改变它从

TransactionList(List<Transaction> userTransactions, {this.transactions});
TransactionList(this.transactions);

关于 flutter | Dart - NoSuchMethodError : The method 'map' was called on null,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/63536823/

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