我再次回到与我已经在堆栈溢出错误中发布的问题相关的问题：'_elements.contains(element)': is not true
这个问题一直困扰着我，但我无法重现同样的问题，现在我以某种方式再次尝试重现，我已经发布了代码让每个人弄清楚我做错了什么导致了这个断言错误和使应用程序崩溃。
我是编程新手，任何帮助将不胜感激。我已经精简了代码，我知道一些错误。但是，唯一的主要问题是Failed assertion: line 3927 pos 14: '_dependents.isEmpty': is not true.和Failed assertion: line 1766 pos 12: '_elements.contains(element)': is not true.
重现步骤。
main.dart
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:untitled1/addnewbranch.dart';
void main() {
runApp(
new MaterialApp(
home: new Branches(),
),
);
}
class ProjectModel {
BranchSetUpModelData branchesModel;
ProjectModel(this.branchesModel);
}
class BranchSetUpModelData {
String branchName;
String hostelType;
String area;
String city;
BranchSetUpModelData(this.branchName, this.hostelType, this.area, this.city);
}
DatabaseReference _branchesRef;
List<ProjectModel> projectModel = new List();
Map data = {};
List<String> mapKeys = new List();
DataSnapshot dataSnapshot;
class Branches extends StatefulWidget {
//const BranchView({ Key key }) : super(key: key);
const Branches({Key key}) : super(key: key);
@override
_BranchesState createState() => new _BranchesState();
}
class _BranchesState extends State<Branches> {
String userUid = '';
String text;
int noOfBranches = 0;
int itemCount;
Future<Null> getUserUid() async {
try {
//FirebaseUser user = await FirebaseAuth.instance.currentUser();
//userUid = user.uid;
//print(userUid);
_branchesRef =
FirebaseDatabase.instance.reference().child('data').child('branches');
print('branchesref = $_branchesRef');
if (_branchesRef != null) {
try {
_branchesRef.once().then((DataSnapshot snapShot) {
dataSnapshot = snapShot;
print(snapShot is Map);
print(dataSnapshot.value);
data = dataSnapshot.value;
print(data is Map);
print(data);
data.forEach((key, value) {
mapKeys.add(key);
});
print('no of branches = $noOfBranches');
projectModel.clear();
mapKeys.forEach((value) {
_branchesRef.child(value).once().then((DataSnapshot b) {
data = b.value;
data.keys.forEach((k) {
BranchSetUpModelData x = new BranchSetUpModelData(
b.value['branchDetails']['branchName'],
b.value['branchDetails']['hostelType'],
b.value['branchDetails']['area'],
b.value['branchDetails']['city'],
);
print('details from for each loop');
ProjectModel projectModelData = new ProjectModel(x);
projectModel.add(projectModelData);
});
print('projectmodel length = ${projectModel.length}');
});
});
setState(() {
noOfBranches = mapKeys.length;
itemCount = noOfBranches;
});
print('no of branches = $noOfBranches');
data.keys.forEach((k) {
print('inside this foreach loop');
print(k);
});
});
} catch (Exception) {
showDialog(
context: context,
child: new AlertDialog(
content: new Text(Exception.message.toString())));
}
} else {
print('user does not exist');
}
} catch (Exception) {
print(Exception.toString());
showDialog(
context: context,
child: new AlertDialog(
content: new Text(Exception.toString()),
));
}
}
@override
void initState() {
super.initState();
mapKeys.clear();
FirebaseDatabase.instance.setPersistenceEnabled(true);
FirebaseDatabase.instance.setPersistenceCacheSizeBytes(10000000);
getUserUid();
/*setState((){
noOfBranches = mapKeys.length;
});*/
print('noOfBranches in init state= $noOfBranches');
}
@override
Widget build(BuildContext context) {
print('noof branches inside widget build = $noOfBranches');
//if(noOfBranches!=0) {
return new MaterialApp(
title: 'Branches',
theme: new ThemeData(
primaryColor: const Color(0xFF229E9C),
),
home: new Scaffold(
appBar: new AppBar(
title: const Text('Branches'),
backgroundColor: Colors.teal[300],
),
floatingActionButton: new FloatingActionButton(
heroTag: 'branchesHeroTag',
child: new Icon(Icons.add),
backgroundColor: Colors.teal[300],
onPressed: (() {
Navigator.push(
context,
new MaterialPageRoute(
builder: (_) => new AddNewBranch(),
),
);
}),
tooltip: 'Add Branch',
),
body: new Container(
child: new ListView.builder(
padding: const EdgeInsets.only(
left: 4.0,
right: 4.0,
),
itemCount: itemCount,
itemBuilder: (BuildContext context, int index) {
if (noOfBranches != 0) {
// children: <Widget>[
return new InkWell(
onTap: (() {
/*Navigate here to a different page*/
}),
child: new Card(
child: new Column(
children: <Widget>[
new Container(
//margin: const EdgeInsets.only(top:16.0),
padding: const EdgeInsets.only(top: 16.0),
child: new Row(
children: <Widget>[
new Expanded(
child: new Row(
children: <Widget>[
new Container(
margin: const EdgeInsets.only(
left: 16.0,
right: 8.0,
top: 4.0,
bottom: 4.0),
child: new IconButton(
icon: new Icon(Icons.call),
onPressed: (() {}))),
new Container(
child: new Text(
'80/125',
style: new TextStyle(
fontSize: 18.0,
),
),
),
],
),
),
new Expanded(
child: new Row(
textDirection: TextDirection.rtl,
children: [
new Container(
margin:
const EdgeInsets.only(right: 16.0),
child: new Text(
projectModel[index]
.branchesModel
.hostelType,
style: new TextStyle(
fontSize: 18.0,
),
),
),
],
),
),
],
),
),
new Container(
margin:
const EdgeInsets.fromLTRB(16.0, 8.0, 16.0, 4.0),
child: new Row(children: <Widget>[
new Text(
projectModel[index].branchesModel.branchName,
style: new TextStyle(
fontSize: 24.0,
),
),
]),
),
new Container(
margin: const EdgeInsets.only(
left: 16.0, right: 16.0, bottom: 8.0),
child: new Row(
children: <Widget>[
new Text(projectModel[index].branchesModel.city),
],
),
),
],
),
),
); // InkWell ends here so this has to go into ListView.builder
} else {
itemCount = 1;
return new Center(
child: new Column(
// mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
'Setup your Hostel',
style: new TextStyle(
fontSize: 24.0,
color: Colors.grey[400],
fontWeight: FontWeight.bold,
),
),
new Text(
'Please click below + icon to Setup your Hostel',
style: new TextStyle(
fontSize: 16.0,
color: Colors.grey[400],
),
),
],
),
);
}
},
), // ListView.builder ends here.
),
),
);
}
}
globals.dart
library my_app.globals;
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_database/firebase_database.dart';
final FirebaseAuth auth = FirebaseAuth.instance;
final DatabaseReference databaseReference = FirebaseDatabase.instance.reference();
添加新分支.dart
import 'dart:async';
import 'package:meta/meta.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:untitled1/main.dart';
import './globals.dart' as gl;
class BranchSetupModel {
String branchName;
String hostelType;
String area;
String city;
BranchSetupModel(this.branchName, this.hostelType, this.area, this.city);
}
BranchSetupModel branchSetupModel =
new BranchSetupModel('', 'Hostel Type', '', '');
class AddNewBranch extends StatefulWidget {
const AddNewBranch({Key key}) : super(key: key);
@override
State<StatefulWidget> createState() {
return new _AddNewBranchState();
}
}
class _AddNewBranchState extends State<AddNewBranch> {
String actionsString = 'Next';
String userUid;
TextEditingController _branchNameController = new TextEditingController();
TextEditingController _areaController = new TextEditingController();
TextEditingController _cityController = new TextEditingController();
final GlobalKey<FormState> _formKey = new GlobalKey<FormState>();
final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
bool _formWasEdited = false;
bool _autovalidate = false;
String dropDownvalue = 'Hostel Type';
//FocusNode _branchManagerNameFocusNode = new FocusNode();
String _validateName(String value) {
_formWasEdited = true;
if (value.isEmpty) return 'Name is required.';
final RegExp nameExp = new RegExp(r'^[A-Za-z ]+$');
if (!nameExp.hasMatch(value))
return 'Please enter only alphabetical characters and spaces.';
return null;
}
Future<Null> getUserUid() async {
try {
FirebaseUser user = await FirebaseAuth.instance.currentUser();
userUid = user.uid;
print(userUid);
} catch (Exception) {
print(Exception.toString());
}
}
@override
void initState() {
super.initState();
getUserUid();
_branchNameController =
new TextEditingController(text: branchSetupModel.branchName);
_areaController = new TextEditingController(text: branchSetupModel.area);
_cityController = new TextEditingController(text: branchSetupModel.city);
dropDownvalue = branchSetupModel.hostelType;
branchSetupModel = new BranchSetupModel('', 'Hostel Type', '', '');
}
@override
Widget build(BuildContext context) {
return new MaterialApp(
theme: new ThemeData(
primarySwatch: Colors.teal,
),
title: 'Branch Setup',
home: new Scaffold(
appBar: new AppBar(
title: const Text('Add New Branch'),
backgroundColor: Colors.teal[300],
leading: new IconButton(
icon: new Icon(Icons.arrow_back),
onPressed: (() {
print('back button clicked');
//to be removed and to include functionality here
Navigator.push(
context,
new MaterialPageRoute(
builder: (_) => new Branches(),
),
);
}),
),
actions: <Widget>[
new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
mainAxisSize: MainAxisSize.min,
children: <Widget>[
new FlatButton(
child: new Text(
actionsString,
style: new TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.w500,
color: Colors.white,
),
),
onPressed: () {
print('Save button clicked');
String pushKey = gl.databaseReference
.child('data')
.child('branches')
.push()
.key;
gl.databaseReference
.child('data')
.child('branches')
.child(pushKey)
.child('branchDetails')
.set({
"branchName": branchSetupModel.branchName,
"hostelType": branchSetupModel.hostelType,
"area": branchSetupModel.area,
"city": branchSetupModel.city,
"pushKey": pushKey
});
Navigator.push(
context,
new MaterialPageRoute(
builder: (_) => new Branches(),
),
);
},
splashColor: const Color(0xFF229E9C),
),
],
),
),
],
),
body: new Form(
key: _formKey,
child: new ListView(
children: <Widget>[
new Container(
margin: const EdgeInsets.only(left: 16.0, right: 16.0),
child: new Row(
children: <Widget>[
new Text('Hostel Type'),
],
),
),
new Container(
//height: 56.0,
margin: const EdgeInsets.only(left: 16.0, right: 16.0),
child: new Column(
children: <Widget>[
new DropdownButton<String>(
//key: _dropDownKey,
hint: new Text(dropDownvalue),
items: <String>[
'Mens',
'Womens',
].map(
(String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
},
).toList(),
onChanged: (String value) {
setState(() {
dropDownvalue = value;
branchSetupModel.hostelType = value;
print(branchSetupModel.hostelType);
});
},
),
],
),
),
new Container(
margin: const EdgeInsets.only(left: 16.0, right: 16.0),
child: new Row(
children: <Widget>[
new Expanded(
child: new TextField(
autocorrect: false,
decoration: new InputDecoration(
labelText: 'Branch Name',
),
controller: _branchNameController,
onChanged: (String value) {
branchSetupModel.branchName =
_branchNameController.text;
print(branchSetupModel.branchName);
},
//validator: _validateName,
),
),
],
),
),
new Container(
margin: const EdgeInsets.only(left: 16.0, right: 16.0),
child: new Row(
children: <Widget>[
new Expanded(
child: new TextField(
decoration: new InputDecoration(
labelText: 'Area/Location',
),
controller: _areaController,
onChanged: (String value) {
branchSetupModel.area = value;
print(branchSetupModel.area);
},
//validator: _validateName,
),
),
],
),
),
new Container(
margin: const EdgeInsets.only(
left: 16.0,
right: 16.0,
),
child: new Row(
children: <Widget>[
new Expanded(
child: new TextField(
decoration: new InputDecoration(
小智 15
我最近在尝试从有状态小部件导航到另一条路线时遇到了同样的异常。原来我忘记super.initState();在小部件的开头添加该行initState()
一旦我把它改成这个，它就完美地工作了
@override
void initState() {
super.initState();
....
}
hma*_*des 10
此错误是由于不正确的小部件配置而发生的，因此换句话说，它本身不是错误，而是另一个错误的症状。
对于OP
OP已经找到解决方案了，我就不多说了。修复你应该的错误ListView就可以了。
长话短说
尝试：
super.initState()你所有的StatefulWidgets.initState()覆盖。Widget.key物品都是独一无二的。builder函数的小部件没有错误。这些小部件包括AnimatedBuilder、LayoutBuilder和外部包（例如GetX或 ）Provider，它们具有构建器，以及任何依赖于它们的包（例如Bloc）。对于这些小部件，当您根据某些传递的值构建相同的不同builder部件时，通常会发生异常。例如：Widgetinstance members...
BlocBuilder<MyBloc, MyState>(
builder: (context, state) => Container(
color: state is SomeState ? Colors.blue : Colors.red, // Something along these lines
),
)
// or
BlocBuilder<MyBloc, MyState>(
builder: (context, state) => state is SomeState ? Container(color: Colors.red) : Container(color: Colors.blue),
)
....
更多说明
首先，我想指出，虽然异常消息有点误导，但 flutter 团队有几个TODOs 来使异常更清晰，并专门指有故障的小部件。
GlobalKey正如消息中提到的，该错误与小部件树中的重复有关。通常，由于Key在两个不同的小部件上直接使用相同的部件而不会发生这种情况（因为开发人员通常都知道这一点）。相反，它隐藏在其他问题后面，例如上面提到的问题。然而，它们都会产生类似的效果：它们会导致小部件的生命周期状态出现错误。
initState例如，忘记调用会扰乱小部件的生命周期状态更新。GlobalKey我不太确定这种情况发生在哪里，但如果小部件的生命周期状态被篡改，框架似乎会为同一个小部件创建重复的元素/小部件。这还需要进一步调查和确认。
小部件的问题builder在于，如果要返回的第一个小部件出现builder异常，框架将挂载它，但由于某种原因，当要返回的第二个小部件插入builder到树中时，生命周期不会发生变化，第一个和第二个小部件最终都具有相同的Key.
在这两种情况下，当框架卸载当前活动的小部件时，它会检查小部件的生命周期状态，确定哪些部件处于非活动状态，然后忽略它们。但是，由于某些小部件的生命周期状态是错误的，因此它可能会将不活动的小部件视为活动的，将其与当前活动的小部件进行比较以查找重复项，然后抛出异常。
如果您想自己检查，可以src/widgets/framework.dart从函数开始读取错误消息中引用的文件BuilderOwner.finalizeTree()。
Mah*_*ahi -6
我的一位同事实际上改变了我构建 ListView.builder 的方式，现在我没有看到错误。我会密切关注这一点，并发布任何新的方法来回答这个问题或再次出现的任何错误。
我只更改了我发布以供参考的 main.dart 文件。
主程序.dart
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:untitled1/addnewbranch.dart';
void main() {
runApp(
new MaterialApp(
home: new Branches(),
),
);
}
class ProjectModel {
BranchSetUpModelData branchesModel;
ProjectModel(this.branchesModel);
}
class BranchSetUpModelData {
String branchName;
String hostelType;
String area;
String city;
BranchSetUpModelData(this.branchName, this.hostelType, this.area, this.city);
}
DatabaseReference _branchesRef;
List<ProjectModel> projectModel = new List();
Map data = {};
List<String> mapKeys = new List();
DataSnapshot dataSnapshot;
class Branches extends StatefulWidget {
//const BranchView({ Key key }) : super(key: key);
const Branches({Key key}) : super(key: key);
@override
_BranchesState createState() => new _BranchesState();
}
class _BranchesState extends State<Branches> {
String userUid = '';
String text;
Future<Null> getUserUid() async {
try {
//FirebaseUser user = await FirebaseAuth.instance.currentUser();
//userUid = user.uid;
//print(userUid);
_branchesRef =
FirebaseDatabase.instance.reference().child('data').child('branches');
print('branchesref = $_branchesRef');
if (_branchesRef != null) {
try {
_branchesRef.once().then((DataSnapshot snapShot) {
dataSnapshot = snapShot;
print(snapShot is Map);
print(dataSnapshot.value);
data = dataSnapshot.value;
print(data is Map);
print(data);
data.forEach((key, value) {
mapKeys.add(key);
});
projectModel.clear();
mapKeys.forEach((value) {
_branchesRef.child(value).once().then((DataSnapshot b) {
data = b.value;
setState(() {
data.keys.forEach((k) {
BranchSetUpModelData x = new BranchSetUpModelData(
b.value['branchDetails']['branchName'],
b.value['branchDetails']['hostelType'],
b.value['branchDetails']['area'],
b.value['branchDetails']['city'],
);
print('details from for each loop');
ProjectModel projectModelData = new ProjectModel(x);
projectModel.add(projectModelData);
});
});
print('projectmodel length = ${projectModel.length}');
});
});
data.keys.forEach((k) {
print('inside this foreach loop');
print(k);
});
});
} catch (Exception) {
showDialog(
context: context,
child: new AlertDialog(
content: new Text(Exception.message.toString())));
}
} else {
print('user does not exist');
}
} catch (Exception) {
print(Exception.toString());
showDialog(
context: context,
child: new AlertDialog(
content: new Text(Exception.toString()),
));
}
}
@override
void initState() {
super.initState();
mapKeys.clear();
FirebaseDatabase.instance.setPersistenceEnabled(true);
FirebaseDatabase.instance.setPersistenceCacheSizeBytes(10000000);
getUserUid();
/*setState((){
noOfBranches = mapKeys.length;
});*/
}
@override
Widget build(BuildContext context) {
//if(noOfBranches!=0) {
return new MaterialApp(
title: 'Branches',
theme: new ThemeData(
primaryColor: const Color(0xFF229E9C),
),
home: new Scaffold(
appBar: new AppBar(
title: const Text('Branches'),
backgroundColor: Colors.teal[300],
),
floatingActionButton: new FloatingActionButton(
heroTag: 'branchesHeroTag',
child: new Icon(Icons.add),
backgroundColor: Colors.teal[300],
onPressed: (() {
Navigator.push(
context,
new MaterialPageRoute(
builder: (_) => new AddNewBranch(),
),
);
}),
tooltip: 'Add Branch',
),
body: (projectModel.length == 0)
? new Center(
child: new Column(
// mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
'Setup your Hostel',
style: new TextStyle(
fontSize: 24.0,
color: Colors.grey[400],
fontWeight: FontWeight.bold,
),
),
new Text(
'Please click below + icon to Setup your Hostel',
style: new TextStyle(
fontSize: 16.0,
color: Colors.grey[400],
),
),
],
),
)
: new Container(
child: new ListView.builder(
padding: const EdgeInsets.only(
left: 4.0,
right: 4.0,
),
itemCount: projectModel.length,
itemBuilder: (BuildContext context, int index) {
// children: <Widget>[
return new InkWell(
onTap: (() {
/*Navigate here to a different page*/
}),
child: new Card(
child: new Column(
children: <Widget>[
new Container(
//margin: const EdgeInsets.only(top:16.0),
padding: const EdgeInsets.only(top: 16.0),
child: new Row(
children: <Widget>[
new Expanded(
child: new Row(
children: <Widget>[
new Container(
margin: const EdgeInsets.only(
left: 16.0,
right: 8.0,
top: 4.0,
bottom: 4.0),
child: new IconButton(
icon: new Icon(Icons.call),
onPressed: (() {}))),
new Container(
child: new Text(
'80/125',
style: new TextStyle(
fontSize: 18.0,
),
),
),
],
),
),
new Expanded(
child: new Row(
textDirection: TextDirection.rtl,
children: [
new Container(
margin: const EdgeInsets.only(
right: 16.0),
child: new Text(
projectModel[index]
.branchesModel
.hostelType,
style: new TextStyle(
fontSize: 18.0,
),
),
),
],
),
),
],
),
),
new Container(
margin: const EdgeInsets.fromLTRB(
16.0, 8.0, 16.0, 4.0),
child: new Row(children: <Widget>[
new Text(
projectModel[index].branchesModel.branchName,
style: new TextStyle(
fontSize: 24.0,
),
),
]),
),
new Container(
margin: const EdgeInsets.only(
left: 16.0, right: 16.0, bottom: 8.0),
child: new Row(
children: <Widget>[
new Text(
projectModel[index].branchesModel.city),
],
),
),
],
),
),
); // InkWell ends here so this has to go into ListView.builder
},
), // ListView.builder ends here.
),
),
);
}
}
我希望这能帮助每个遇到相同用例的人解决他们的问题，非常感谢。马希。
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