问题
I am new to Flutter but I am trying to create a DropdownButtonFormField and it is not working. I am getting an error that says I have duplicate values. What is interesting is that I do not have a list with duplicate values. I have found a similar question on SO and the solution says to initiate the strings with a value and that the user was duplicating a list item, but I have a similar solution for another another list and it seems to work fine. I cannot figure out why it is not working here. Any help is greatly appreciated.
Error Message:
There should be exactly one item with [DropdownButton]'s value: 0.
Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
'package:flutter/src/material/dropdown.dart':
Failed assertion: line 1411 pos 15: 'items == null || items.isEmpty || value == null ||
items.where((DropdownMenuItem<T> item) {
return item.value == value;
}).length == 1'
The relevant error-causing widget was:
StreamBuilder<UserProfile>
ProfileForm Class:
final List<String> accountType = ['Educator', 'School Administrator', 'Parent'];
String _currentAccountType;
@override
Widget build(BuildContext context) {
final user = Provider.of<User>(context);
return StreamBuilder<UserProfile>(
stream: DatabaseService(uid: user.uid).userProfileData,
builder: (context, snapshot) {
if (snapshot.hasData) {
UserProfile userProfileData = snapshot.data;
return Form(
key: _formKey,
child: Column(
children: <Widget>[
SizedBox(height: 20.0),
DropdownButtonFormField(
decoration: textInputDecoration,
value: _currentAccountType ?? userProfileData.accountType,
items: accountType.map((accountType) {
return DropdownMenuItem(
value: accountType,
child: Text(accountType),
);
}).toList(),
onChanged: (val) {
setState(() {
_currentAccountType = val;
});
},
),
Database Class
class DatabaseService {
final String uid;
DatabaseService({this.uid});
final CollectionReference userProfileCollection =
Firestore.instance.collection('user_profile');
Future updateUserProfile(
String accountType,
String birthDate,
String courseName,
String dateJoined,
String email,
String firstName,
String lastName,
String schoolName,
String title) async {
return await userProfileCollection.document(uid).setData({
'accountType': accountType,
'birthDate': birthDate,
'courseName': courseName,
'dateJoined': dateJoined,
'email': email,
'firstName': firstName,
'lastName': lastName,
'schoolName': schoolName,
'title': title,
});
}
//User Profile from snapshot
List<Profile> _userProfileListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.documents.map((doc) {
return Profile(
accountType: doc.data['accountType'] ?? '',
birthDate: doc.data['birthDate'] ?? '',
courseName: doc.data['courseName'] ?? '',
dateJoined: doc.data['dateJoined'] ?? '',
email: doc.data['email'] ?? '',
firstName: doc.data['firstName'] ?? '',
lastName: doc.data['lastName'] ?? '',
schoolName: doc.data['schoolName'] ?? '',
title: doc.data['title'] ?? '',
);
}).toList();
}
UserProfile _userProfileFromSnapshot(DocumentSnapshot snapshot) {
return UserProfile(
uid: uid,
accountType: snapshot.data['accountType'],
birthDate: snapshot.data['birthDate'],
courseName: snapshot.data['courseName'],
dateJoined: snapshot.data['dateJoined'],
email: snapshot.data['email'],
firstName: snapshot.data['firstName'],
lastName: snapshot.data['lastName'],
schoolName: snapshot.data['schoolName'],
title: snapshot.data['title'],
);
}
Stream<List<Profile>> get userProfile {
return userProfileCollection.snapshots().map(_userProfileListFromSnapshot);
}
Stream<UserProfile> get userProfileData {
return userProfileCollection
.document(uid)
.snapshots()
.map(_userProfileFromSnapshot);
}
}
回答1:
userProfileData.accountType is '0', not 'Educator' or 'School Administrator' or 'Parent'.
Success: value must in items.value
final List<String> accountType = ['Educator', 'School Administrator', 'Parent'];
DropdownButtonFormField(
decoration: textInputDecoration,
value: accountType[0],
items: accountType.map((accountType) {
return DropdownMenuItem(
value: accountType,
child: Text(accountType),
);
}).toList(),
onChanged: (val) {
setState(() {
_currentAccountType = val;
});
},
),
Failed: There should be exactly one item with [DropdownButton]'s value: hahaha
final List<String> accountType = ['Educator', 'School Administrator', 'Parent'];
DropdownButtonFormField(
decoration: textInputDecoration,
value: 'hahaha',
items: accountType.map((accountType) {
return DropdownMenuItem(
value: accountType,
child: Text(accountType),
);
}).toList(),
onChanged: (val) {
setState(() {
_currentAccountType = val;
});
},
),
回答2:
In my case, below change resolved the error:
Error scenario:
var itemList=['Alpha','Beta','Cat'];
var itemSelected='Zebra';
Working scenario:
var itemList=['Alpha','Beta','Cat'];
var itemSelected='Cat'; //Can be Alpha, Beta or Cat but not any other value
Dropdown widget code:
DropdownButton<String>(
items: itemList.map((String singleItem){
return DropdownMenuItem<String>(
value: singleItem,
child:Text(singleItem)
);
}).toList(),
onChanged: (String itemChosen){
setState(() {
this.itemSelected=itemChosen;
});
},
value:itemSelected ,
),
Having the 'itemSelected' variable value same as one of the elements in the list resolved the problem for me.
回答3:
I also encountered this case, but there is no workaround for you to help me see where the error code is?
var dataLv2 = new List<DropdownMenuItem<String>>();
var dataLv3 = new List<DropdownMenuItem<String>>();
Widget widgetLoaiViPham() {
return StreamBuilder(
initialData: "KHONG",
stream: widget.bloc.subject_ketluan_cmis_loai_vipham_stream,
builder: (context, snapshot) {
return DropdownButtonFormField(
value: snapshot.data,
items: getDropDownMenuLv1(),
decoration: InputDecoration(labelText: "Loại vi phạm"),
onChanged: (newVal) {
dataLv2 = defaultVal2(newVal);
var tempVal2 = dataLv2.length > 0 ? dataLv2.first.value : null;
dataLv3 = defaultVal3(tempVal2);
var tempVal3 = dataLv3.length > 0 ? dataLv3.first.value : null;
widget.bloc.subject_ketluan_cmis_loai_vipham_sink.add(newVal);
widget.bloc.subject_ketluan_cmis_loai_kiemtra_sink.add(tempVal2);
widget.bloc.subject_ketluan_cmis_loai_xuly_sink.add(tempVal3);
},
);
},
);
}
Widget widgetLoaiKiemTra() {
return StreamBuilder(
initialData: null,
stream: widget.bloc.subject_ketluan_cmis_loai_kiemtra_stream,
builder: (context, snapshot) {
return DropdownButtonFormField(
value: null,
items: dataLv2,
decoration: InputDecoration(labelText: "Loại kiểm tra"),
onChanged: (newVal) {
dataLv3 = defaultVal3(newVal);
var tempVal3 = dataLv3.length > 0 ? dataLv3.first.value : null;
widget.bloc.subject_ketluan_cmis_loai_kiemtra_sink.add(newVal);
widget.bloc.subject_ketluan_cmis_loai_xuly_sink.add(tempVal3);
},
);
},
);
}
When changing the widgetLoaiViPham, the data of the widgetLoaiKiemTra will change according to everything is normal, but when I change the widgetLoaiKiemTra and then I continue to change the widgetLoaiViPham, an error will occur.
Although debugging, the value and items of widgetLoaiKiemTra match
来源：https://stackoverflow.com/questions/59925233/either-zero-or-2-or-more-dropdownmenuitems-were-detected-with-the-same-value