flutter validate radio buttons

问题

How can I add a validator function to a list of RadioButtons in order to have them validated (like TextFormFields with _formKey.currentState.validate()) after the User submits the Form?

回答1:

You can copy paste run full code below
You can use package https://pub.dev/packages/flutter_form_builder
It support bulid-in validators such as FormBuilderValidators.required() you can directly use
you can also use custom validator function https://pub.dev/packages/flutter_form_builder#custom-validator-function

FormBuilderRadio(
                      decoration:
                          InputDecoration(labelText: 'My chosen language'),
                      attribute: "best_language",
                      leadingInput: true,
                      onChanged: _onChanged,
                      validators: [FormBuilderValidators.required()],
                      options:
                          ["Dart", "Kotlin", "Java", "Swift", "Objective-C"]
                              .map((lang) => FormBuilderFieldOption(
                                    value: lang,
                                    child: Text('$lang'),
                                  ))
                              .toList(growable: false),
                    ),

working demo

full code

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_form_builder/flutter_form_builder.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,
        inputDecorationTheme: InputDecorationTheme(
          labelStyle: TextStyle(color: Colors.purple),
        ),
      ),
      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>();

  ValueChanged _onChanged = (val) => print(val);
  var genderOptions = ['Male', 'Female', 'Other'];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("FormBuilder Example"),
      ),
      body: Padding(
        padding: EdgeInsets.all(10),
        child: SingleChildScrollView(
          child: Column(
            children: <Widget>[
              FormBuilder(
                // context,
                key: _fbKey,
                autovalidate: true,
                initialValue: {
                  'movie_rating': 5,
                },
                readOnly: false,
                child: Column(
                  children: <Widget>[
                    FormBuilderRadio(
                      decoration:
                          InputDecoration(labelText: 'My chosen language'),
                      attribute: "best_language",
                      leadingInput: true,
                      onChanged: _onChanged,
                      validators: [FormBuilderValidators.required()],
                      options:
                          ["Dart", "Kotlin", "Java", "Swift", "Objective-C"]
                              .map((lang) => FormBuilderFieldOption(
                                    value: lang,
                                    child: Text('$lang'),
                                  ))
                              .toList(growable: false),
                    ),
                  ],
                ),
              ),
              Row(
                children: <Widget>[
                  Expanded(
                    child: MaterialButton(
                      color: Theme.of(context).accentColor,
                      child: Text(
                        "Submit",
                        style: TextStyle(color: Colors.white),
                      ),
                      onPressed: () {
                        if (_fbKey.currentState.saveAndValidate()) {
                          print(_fbKey.currentState.value);
                        } else {
                          print(_fbKey.currentState.value);
                          print("validation failed");
                        }
                      },
                    ),
                  ),
                  SizedBox(
                    width: 20,
                  ),
                  Expanded(
                    child: MaterialButton(
                      color: Theme.of(context).accentColor,
                      child: Text(
                        "Reset",
                        style: TextStyle(color: Colors.white),
                      ),
                      onPressed: () {
                        _fbKey.currentState.reset();
                      },
                    ),
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}

来源：https://stackoverflow.com/questions/61368025/flutter-validate-radio-buttons