方法 '[]' 不能无条件调用，因为接收者可以是 'null' [英] The method '[]' can't be unconditionally invoked because the receiver can be 'null'
本文介绍了方法 '[]' 不能无条件调用，因为接收者可以是 'null'的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我是 Flutter 的新手.我正在尝试开发一个应用程序.
I'm new to Flutter. I am trying to develop an application.
我想显示 Firebase 数据库中的人员列表.但是，我收到以下错误.
I want to show the staff list in the Firebase database. However, I am getting the following error.
错误:
方法'[]'不能无条件调用，因为接收者可以为空".尝试使呼叫有条件(使用 '?.')或添加对目标的空检查 ('!').
The method '[]' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').
科德拉姆:
`import 'package:calendar/page/mainPage.dart';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
class Staff extends StatefulWidget {
@override
_StaffState createState() => _StaffState();
}
class _StaffState extends State<Staff> {
final _firestore = FirebaseFirestore.instance;
@override
Widget build(BuildContext context) {
// ignore: unused_local_variable
CollectionReference staffRef = _firestore.collection('staff');
return Scaffold(
appBar: AppBar(
title: Text("Personel Listesi"),
backgroundColor: Colors.redAccent[400],
actions: <Widget>[
IconButton(
icon: Icon(Icons.home),
onPressed: () {
Navigator.pushAndRemoveUntil(
context,
MaterialPageRoute(builder: (_) => MainPage()),
(route) => true);
},
),
],
),
body: Container(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Center(
child: Column(
children: [
StreamBuilder<QuerySnapshot>(
stream: staffRef.snapshots(),
builder: (BuildContext context, AsyncSnapshot asyncSnapshot) {
if (asyncSnapshot.hasError) {
return Center(
child: Text(
"Bir hata oluştu, lütfen tekrar deneyiniz."));
} else {
if (asyncSnapshot.hasData) {
List<DocumentSnapshot> listStaff =
asyncSnapshot.data.docs;
return Flexible(
child: ListView.builder(
itemBuilder: (context, index) {
return Card(
elevation: 20,
color: Colors.greenAccent[200],
child: ListTile(
trailing: IconButton(
icon: Icon(Icons.delete),
onPressed: () async {
await listStaff[index]
.reference
.delete();
},
),
title: Text(
'${listStaff[index].data['nameSurname']}',
style: TextStyle(fontSize: 20),
),
subtitle: Column(
children: [
Row(
mainAxisAlignment:
MainAxisAlignment.start,
children: [
Text(
'${listStaff[index].data['tip']}',
style: TextStyle(fontSize: 14),
),
],
),
Row(
mainAxisAlignment:
MainAxisAlignment.start,
children: [
Text(
'${listStaff[index].data['mail']}',
style: TextStyle(fontSize: 14),
),
],
),
Row(
mainAxisAlignment:
MainAxisAlignment.start,
children: [
Text(
'${listStaff[index].data['phone']}',
style: TextStyle(fontSize: 14),
),
],
),
],
),
),
);
},
itemCount: listStaff.length),
);
} else {
return Center(
child: CircularProgressIndicator(),
);
}
}
},
),
],
),
),
),
),
);
}
}
`
推荐答案
在新的flutter更新中，我们不需要添加.data()
In the new flutter update, we don't need to add .data()
我的代码如下
title: Text(
**'${listStaff[index].data['nameSurname']}',**
style: TextStyle(fontSize: 20),
),
像这样改变它修复了错误.
title: Text(
**'${listPersonel[index]['nameSurname']}'**,
style: TextStyle(fontSize: 20),
),
这篇关于方法 '[]' 不能无条件调用，因为接收者可以是 'null'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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