How to validate drop down in flutter - validation

Question

I've created on the dropdown and i want to validate that dropdown. when a user doesn't select an item from drop-down then it will show a validation.
here is some code I've tried so far.
in this code I've created one drop down when I am click submit then it will show a validation when the user doesn't select an item from the dropdown.
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Dropdown Validation',
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List<String> _type = <String>[
'Passport',
'Driving License',
'Voter ID card',
'Ration Card',
'Aadhar',
'Other Id'
];
String type = 'Local Goverment';
Widget _buildlicenseissuingauthority() {
return FormField(
builder: (FormFieldState state) {
return InputDecorator(
decoration: InputDecoration(
prefixIcon: Icon(Icons.location_on),
labelText: 'Select Personal Identification type',
),
isEmpty: type == '',
child: new DropdownButtonHideUnderline(
child: new DropdownButton(
value: type,
isDense: true,
onChanged: (String newValue) {
setState(() {
type = newValue;
});
},
items: _type.map(
(String value) {
return new DropdownMenuItem(
value: value,
child: new Text(value),
);
},
).toList(),
),
),
);
},
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Demo'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[_buildlicenseissuingauthority()],
),
),
);
}
}

Answer 1

please use pacakge https://pub.dev/packages/flutter_form_builder
github https://github.com/danvick/flutter_form_builder
It has more than 10 buildin validators, in your case FormBuilderValidators.required()
code snippet
FormBuilderDropdown(
attribute: "gender",
decoration: InputDecoration(
labelText: "Gender",
icon: const Icon(Icons.category),
hintText: "Select hint",
),
// initialValue: 'Male',
onChanged: _onChanged,
hint: Text('Select Gender'),
validators: [FormBuilderValidators.required()],
items: ['Male', 'Female', 'Other']
.map((gender) => DropdownMenuItem(
value: gender,
child: Text('$gender'),
))
.toList(),
)
full example code
import 'package:datetime_picker_formfield/datetime_picker_formfield.dart';
import 'package:flutter/material.dart';
import 'package:flutter_form_builder/flutter_form_builder.dart';
import 'package:intl/intl.dart';
import './data.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter FormBuilder Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
#override
MyHomePageState createState() {
return MyHomePageState();
}
}
class MyHomePageState extends State<MyHomePage> {
var data;
bool autoValidate = true;
bool readOnly = false;
bool showSegmentedControl = true;
final GlobalKey<FormBuilderState> _fbKey = GlobalKey<FormBuilderState>();
final GlobalKey<FormFieldState> _specifyTextFieldKey =
GlobalKey<FormFieldState>();
final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();
ValueChanged _onChanged = (val) => print(val);
#override
Widget build(BuildContext context) {
return Scaffold(
key: _scaffoldKey,
appBar: AppBar(
title: Text("FormBuilder Example"),
),
body: Padding(
padding: EdgeInsets.all(10),
child: SingleChildScrollView(
child: Column(
children: <Widget>[
FormBuilder(
// context,
key: _fbKey,
autovalidate: true,
// readonly: true,
child: Column(
children: <Widget>[
FormBuilderCustomField(
attribute: "name",
validators: [
FormBuilderValidators.required(),
],
formField: FormField(
// key: _fieldKey,
enabled: true,
builder: (FormFieldState<dynamic> field) {
return InputDecorator(
decoration: InputDecoration(
icon: const Icon(Icons.laptop),
hintText: "Select hint",
labelText: "Select option",
contentPadding:
EdgeInsets.only(top: 10.0, bottom: 0.0),
border: InputBorder.none,
errorText: field.errorText,
),
child: DropdownButton(
isExpanded: true,
items: ["One", "Two"].map((option) {
return DropdownMenuItem(
child: Text("$option"),
value: option,
);
}).toList(),
value: field.value,
onChanged: (value) {
field.didChange(value);
},
),
);
},
),
),
FormBuilderChipsInput(
decoration: InputDecoration(
labelText: "Chips",
icon: const Icon(Icons.person),
hintText: "Select hint",
),
attribute: 'chips_test',
// readonly: true,
onChanged: _onChanged,
// valueTransformer: (val) => val.length > 0 ? val[0] : null,
initialValue: [
Contact('Andrew', 'stock#man.com',
'https://d2gg9evh47fn9z.cloudfront.net/800px_COLOURBOX4057996.jpg'),
],
maxChips: 5,
findSuggestions: (String query) {
if (query.length != 0) {
var lowercaseQuery = query.toLowerCase();
return mockResults.where((profile) {
return profile.name
.toLowerCase()
.contains(query.toLowerCase()) ||
profile.email
.toLowerCase()
.contains(query.toLowerCase());
}).toList(growable: false)
..sort((a, b) => a.name
.toLowerCase()
.indexOf(lowercaseQuery)
.compareTo(b.name
.toLowerCase()
.indexOf(lowercaseQuery)));
} else {
return const <Contact>[];
}
},
chipBuilder: (context, state, profile) {
return InputChip(
key: ObjectKey(profile),
label: Text(profile.name),
avatar: CircleAvatar(
backgroundImage: NetworkImage(profile.imageUrl),
),
onDeleted: () => state.deleteChip(profile),
materialTapTargetSize:
MaterialTapTargetSize.shrinkWrap,
);
},
suggestionBuilder: (context, state, profile) {
return ListTile(
key: ObjectKey(profile),
leading: CircleAvatar(
backgroundImage: NetworkImage(profile.imageUrl),
),
title: Text(profile.name),
subtitle: Text(profile.email),
onTap: () => state.selectSuggestion(profile),
);
},
),
FormBuilderDateTimePicker(
attribute: "date",
onChanged: _onChanged,
inputType: InputType.date,
format: DateFormat("yyyy-MM-dd"),
decoration: InputDecoration(
labelText: "Appointment Time",
icon: const Icon(Icons.calendar_today),
hintText: "Select hint",
),
// readonly: true,
),
FormBuilderSlider(
attribute: "slider",
validators: [FormBuilderValidators.min(6)],
onChanged: _onChanged,
min: 0.0,
max: 10.0,
initialValue: 1.0,
divisions: 20,
decoration: InputDecoration(
labelText: "Number of somethings",
icon: const Icon(Icons.snooze),
hintText: "Select hint",
),
),
FormBuilderCheckbox(
decoration: InputDecoration(
labelText: "terms",
icon: const Icon(Icons.subject),
hintText: "Select hint",
),
attribute: 'accept_terms',
initialValue: false,
onChanged: _onChanged,
leadingInput: true,
label: Text(
"I have read and agree to the terms and conditions"),
validators: [
FormBuilderValidators.requiredTrue(
errorText:
"You must accept terms and conditions to continue",
),
],
),
FormBuilderDropdown(
attribute: "gender",
decoration: InputDecoration(
labelText: "Gender",
icon: const Icon(Icons.category),
hintText: "Select hint",
),
// initialValue: 'Male',
onChanged: _onChanged,
hint: Text('Select Gender'),
validators: [FormBuilderValidators.required()],
items: ['Male', 'Female', 'Other']
.map((gender) => DropdownMenuItem(
value: gender,
child: Text('$gender'),
))
.toList(),
),
FormBuilderTextField(
attribute: "age",
decoration: InputDecoration(
labelText: "Age",
icon: const Icon(Icons.accessibility),
hintText: "Select hint",
),
onChanged: _onChanged,
valueTransformer: (text) => num.tryParse(text),
validators: [
FormBuilderValidators.numeric(),
FormBuilderValidators.max(70),
],
),
FormBuilderTypeAhead(
// initialValue: "Canada",
decoration: InputDecoration(
labelText: "Country",
icon: const Icon(Icons.golf_course),
hintText: "Select hint",
),
attribute: 'country',
onChanged: _onChanged,
itemBuilder: (context, country) {
return ListTile(
title: Text(country),
);
},
suggestionsCallback: (query) {
if (query.length != 0) {
var lowercaseQuery = query.toLowerCase();
return allCountries.where((country) {
return country
.toLowerCase()
.contains(lowercaseQuery);
}).toList(growable: false)
..sort((a, b) => a
.toLowerCase()
.indexOf(lowercaseQuery)
.compareTo(
b.toLowerCase().indexOf(lowercaseQuery)));
} else {
return allCountries;
}
},
),
FormBuilderRadio(
decoration: InputDecoration(
labelText: 'My chosen language',
icon: const Icon(Icons.language),
hintText: "Select hint",
),
attribute: "best_language",
leadingInput: true,
onChanged: _onChanged,
validators: [FormBuilderValidators.required()],
options: [
"Dart",
"Kotlin",
"Java",
"Swift",
"Objective-C"
]
.map((lang) => FormBuilderFieldOption(value: lang))
.toList(growable: false),
),
FormBuilderSegmentedControl(
decoration: InputDecoration(
labelText: "Movie Rating (Archer)",
icon: const Icon(Icons.crop_rotate),
hintText: "Select hint",
),
attribute: "movie_rating",
options: List.generate(5, (i) => i + 1)
.map(
(number) => FormBuilderFieldOption(value: number))
.toList(),
onChanged: _onChanged,
),
FormBuilderSwitch(
decoration: InputDecoration(
labelText: "conditions",
icon: const Icon(Icons.dashboard),
hintText: "Select hint",
),
label: Text('I Accept the tems and conditions'),
attribute: "accept_terms_switch",
initialValue: true,
onChanged: _onChanged,
),
FormBuilderStepper(
decoration: InputDecoration(
labelText: "Stepper",
icon: const Icon(Icons.account_box),
hintText: "Select hint",
),
attribute: "stepper",
initialValue: 10,
step: 1,
validators: [
(val) {
if (!_fbKey.currentState.fields["accept_terms_switch"]
.currentState.value &&
val >= 10) {
return "You can only put more than 10 if you've accepted terms";
}
}
],
),
FormBuilderRate(
decoration: InputDecoration(
labelText: "Rate this form",
icon: const Icon(Icons.branding_watermark),
hintText: "Select hint",
),
attribute: "rate",
iconSize: 32.0,
initialValue: 1,
max: 5,
onChanged: _onChanged,
),
FormBuilderCheckboxList(
decoration: InputDecoration(
labelText: "The language of my people",
icon: const Icon(Icons.collections),
hintText: "Select hint",
),
attribute: "languages",
initialValue: ["Dart"],
leadingInput: true,
options: [
FormBuilderFieldOption(value: "Dart"),
FormBuilderFieldOption(value: "Kotlin"),
FormBuilderFieldOption(value: "Java"),
FormBuilderFieldOption(value: "Swift"),
FormBuilderFieldOption(value: "Objective-C"),
],
onChanged: _onChanged,
),
FormBuilderCustomField(
attribute: 'custom',
valueTransformer: (val) {
if (val == "Other")
return _specifyTextFieldKey.currentState.value;
return val;
},
formField: FormField(
builder: (FormFieldState<String> field) {
var languages = [
"English",
"Spanish",
"Somali",
"Other"
];
return InputDecorator(
decoration: InputDecoration(
labelText: "What's your preferred language?",
icon: const Icon(Icons.bug_report),
hintText: "Select hint",
),
child: Column(
children: languages
.map(
(lang) => Row(
children: <Widget>[
Radio<dynamic>(
value: lang,
groupValue: field.value,
onChanged: (dynamic value) {
field.didChange(lang);
},
),
lang != "Other"
? Text(lang)
: Expanded(
child: Row(
children: <Widget>[
Text(
lang,
),
SizedBox(width: 20),
Expanded(
child: TextFormField(
key:
_specifyTextFieldKey,
),
),
],
),
),
],
),
)
.toList(growable: false),
),
);
},
),
),
FormBuilderSignaturePad(
decoration: InputDecoration(
labelText: "Signature",
icon: const Icon(Icons.card_travel),
hintText: "Select hint",
),
attribute: "signature",
// height: 250,
clearButtonText: "Start Over",
onChanged: _onChanged,
),
],
),
),
Row(
children: <Widget>[
Expanded(
child: MaterialButton(
color: Theme.of(context).accentColor,
child: Text(
"Submit",
style: TextStyle(color: Colors.white),
),
onPressed: () {
_fbKey.currentState.save();
if (_fbKey.currentState.validate()) {
print(_fbKey.currentState.value);
} else {
print(_fbKey.currentState.value);
print("validation failed");
_scaffoldKey.currentState.showSnackBar(
SnackBar(
content: Text('Validation failed'),
duration: Duration(seconds: 3),
));
}
},
),
),
SizedBox(
width: 20,
),
Expanded(
child: MaterialButton(
color: Theme.of(context).accentColor,
child: Text(
"Reset",
style: TextStyle(color: Colors.white),
),
onPressed: () {
_fbKey.currentState.reset();
},
),
),
],
),
],
),
),
),
);
}
}
Data.dart
class Contact {
final String name;
final String email;
final String imageUrl;
const Contact(this.name, this.email, this.imageUrl);
#override
bool operator ==(Object other) =>
identical(this, other) ||
other is Contact &&
runtimeType == other.runtimeType &&
name == other.name;
#override
int get hashCode => name.hashCode;
#override
String toString() {
return name;
}
}
const allCountries = [
"Afghanistan",
"Albania",
"Algeria",
"American Samoa",
"Andorra",
"Angola",
"Anguilla",
];
const contacts = <Contact>[
Contact('Andrew', 'stock#man.com',
'https://d2gg9evh47fn9z.cloudfront.net/800px_COLOURBOX4057996.jpg'),
Contact('Paul', 'paul#google.com',
'https://mbtskoudsalg.com/images/person-stock-image-png.png'),
Contact('Fred', 'fred#google.com',
'https://media.istockphoto.com/photos/feeling-great-about-my-corporate-choices-picture-id507296326'),
Contact('Brian', 'brian#flutter.io',
'https://upload.wikimedia.org/wikipedia/commons/7/7c/Profile_avatar_placeholder_large.png'),
];
demo, after click submit button, you can see gender has red text "This field can not be empty"

Answer 2

Flutter already has its own Form DropDownButtom for this
List<String> typeNeg = [
"One",
"Two",
"Three",];
String dropdownValue = "One";
DropdownButtonFormField<String>(
value: dropdownValue,
hint: Text("Type of business"),
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
},
validator: (String value) {
if (value?.isEmpty ?? true) {
return 'Please enter a valid type of business';
}
},
items: typeNeg
.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
onSaved: (val) => setState(() => _user.typeNeg = val),
),