Flutter: Multiple widgets used the same GlobalKey or Duplicate GlobalKeys - flutter

Question

I am trying to create a dynamic form and using TextFormField for validation purpose.
Below is the code that is giving error Multiple widgets used the same GlobalKey or Duplicate Global key.
I am not sure how can i fix this or how can i make Dynamic Form clean as per standard.
import 'package:flutter/material.dart';
class App extends StatefulWidget {
#override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
String person;
String age;
String job;
var nameTECs = <TextEditingController>[];
var ageTECs = <TextEditingController>[];
var jobTECs = <TextEditingController>[];
var cards = <Card>[];
var nameController = TextEditingController();
var ageController = TextEditingController();
var jobController = TextEditingController();
#override
void initState() {
super.initState();
cards.add(createCard());
}
Card createCard() {
nameTECs.add(nameController);
ageTECs.add(ageController);
jobTECs.add(jobController);
return Card(
child:new Form(
key: _formKey,
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
Text('Person ${cards.length + 1}'),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: nameController,
decoration: InputDecoration(labelText: 'Full Name'),
validator: validatetext,
onSaved: (String val) {
person = val;
},
),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: ageController,
decoration: InputDecoration(labelText: 'Age'),
validator: validatetext,
onSaved: (String val) {
age = val;
},
),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: jobController,
decoration: InputDecoration(labelText: 'Study/ job'),
validator: validatetext,
onSaved: (String val) {
job = val;
},
),
],
),
),
);
}
void _validateInputs() {
print('button');
if (_formKey.currentState.validate()) {
// If all data are correct then save data to out variables
_formKey.currentState.save();
_onDone();
}
}
_onDone() {
List<PersonEntry> entries = [];
for (int i = 0; i < cards.length; i++) {
var name = nameTECs[i].text;
var age = ageTECs[i].text;
var job = jobTECs[i].text;
entries.add(PersonEntry(name, age, job));
}
Navigator.pop(context, entries);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Column(
children: <Widget>[
Expanded(
child: ListView.builder(
itemCount: cards.length,
itemBuilder: (BuildContext context, int index) {
return cards[index];
},
),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: RaisedButton(
child: Text('Add new'),
onPressed: () => setState(() => cards.add(createCard())),
),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: RaisedButton(
child: Text('Remove last'),
onPressed: () => setState(() => cards.removeLast()),
),
)
],
),
floatingActionButton:
FloatingActionButton(child: Icon(Icons.save), onPressed: _validateInputs),
);
}
}
class PersonEntry {
final String name;
final String age;
final String studyJob;
PersonEntry(this.name, this.age, this.studyJob);
#override
String toString() {
return 'Person: name= $name, age= $age, study job= $studyJob';
}
}
String validatetext(String value) {
if (value.length < 5)
return 'More than 5 char is required';
else
return null;
}
In case someone wants full error.
The following assertion was thrown while finalizing the widget tree:
Multiple widgets used the same GlobalKey.
The key [LabeledGlobalKey<FormState>#89788] was used by multiple widgets. The parents of those widgets were:
- Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null, hintOverrides: null, renderObject: RenderSemanticsAnnotations#65de2 relayoutBoundary=up10)
- Semantics(container: false, properties: SemanticsProperties, label: null, value: null, hint: null, hintOverrides: null, renderObject: RenderSemanticsAnnotations#f4085 relayoutBoundary=up10)
A GlobalKey can only be specified on one widget at a time in the widget tree.
When the exception was thrown, this was the stack
#0 GlobalKey._debugVerifyGlobalKeyReservation.<anonymous closure>.<anonymous closure>.<anonymous closure>
package:flutter/…/widgets/framework.dart:246
#1 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
#2 GlobalKey._debugVerifyGlobalKeyReservation.<anonymous closure>.<anonymous closure>
package:flutter/…/widgets/framework.dart:193
#3 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
#4 GlobalKey._debugVerifyGlobalKeyReservation.<anonymous closure>

Answer 1

The issue is You're using the same key _formKey when for all your forms. You can create a List of _formKeys that contains Globalkey<FormState> and key adding or removing to it based on the length of your cards.
I added a demo using your code as an example:
class App extends StatefulWidget {
#override
_AppState createState() => _AppState();
}
class _AppState extends State<App> {
List<GlobalKey<FormState>> _formKeys = [
GlobalKey<FormState>()
]; // create a list of form keys
String person;
String age;
String job;
var nameTECs = <TextEditingController>[];
var ageTECs = <TextEditingController>[];
var jobTECs = <TextEditingController>[];
var cards = <Card>[];
var nameController = TextEditingController();
var ageController = TextEditingController();
var jobController = TextEditingController();
#override
void initState() {
super.initState();
cards.add(createCard());
}
Card createCard() {
nameTECs.add(nameController);
ageTECs.add(ageController);
jobTECs.add(jobController);
return Card(
child: new Form(
key: _formKeys[_formKeys.length-1], // acess each form key here
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
Text('Person ${cards.length + 1}'),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: nameController,
decoration: InputDecoration(labelText: 'Full Name'),
validator: validatetext,
onSaved: (String val) {
person = val;
},
),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: ageController,
decoration: InputDecoration(labelText: 'Age'),
validator: validatetext,
onSaved: (String val) {
age = val;
},
),
TextFormField(
style: TextStyle(color: Colors.blue),
controller: jobController,
decoration: InputDecoration(labelText: 'Study/ job'),
validator: validatetext,
onSaved: (String val) {
job = val;
},
),
],
),
),
);
}
void _validateInputs() {
print('button');
for (int i = 0; i < _formKeys.length; i++) { // validate the form keys here
if (_formKeys[i].currentState.validate()) {
// validate each form
// If all data are correct then save data to out variables
_formKeys[i].currentState.save(); // dave each form
_onDone();
}
}
}
_onDone() {
List<PersonEntry> entries = [];
for (int i = 0; i < cards.length; i++) {
var name = nameTECs[i].text;
var age = ageTECs[i].text;
var job = jobTECs[i].text;
entries.add(PersonEntry(name, age, job));
}
Navigator.pop(context, entries);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Column(
children: <Widget>[
Expanded(
child: ListView.builder(
itemCount: cards.length,
itemBuilder: (BuildContext context, int index) {
return cards[index];
},
),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: RaisedButton(
child: Text('Add new'),
onPressed: () => setState(
() {
_formKeys.add(GlobalKey<FormState>()); // add a new form key
cards.add(createCard());
},
),
),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: RaisedButton(
child: Text('Remove last'),
onPressed: () => setState(() {
cards.removeLast();
_formKeys.removeLast(); // remove the last form key
}),
),
)
],
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.save), onPressed: _validateInputs),
);
}
}
class PersonEntry {
final String name;
final String age;
final String studyJob;
PersonEntry(this.name, this.age, this.studyJob);
#override
String toString() {
return 'Person: name= $name, age= $age, study job= $studyJob';
}
}
String validatetext(String value) {
if (value.length < 5)
return 'More than 5 char is required';
else
return null;
}
RESULT:
NOTE: The answer is mainly focused on solving the issue of the GlobalKey, if you type in a Form it updates value in every Form because you are using the same controllers for the Forms, you can fix it by also creating a List of Controllers for your TextFormFields.

Answer 2

You're using the same key _formKey when creating a card and adding it to the list card, you should create a global key for each card as a list of the same size of cards, so every time you add/remove a card you do the same to the list of global key