Dart / flutter: how to build a form with multiple user input fields easily

This is not possible. Only children of an InheritedWidget can access it's properties

The solution would be to have your InheritedWidget somewhere above your Button. But that imply you'd have to refactor to take this into account.

Following Rémi's remarks, I came up with a working solution, albeit I'm pretty sure it is not the best and not to be followed on a massive scale, but should work fine for a couple of fields.

The solution comes by handling all TextField widgets inside one single State, alongside the e-mail composition.

In order to achieve a relatively clean code, we can use a custom function that build an input field with the appropriate data label, which accepts two input parameters: a String and a TextEditingController.

The label is also used to determine which variable the setState() method will pass the newly submitted text.

Widget buildTextInputRow(var label, TextEditingController textEditingController) {    return new ListView(      shrinkWrap: true,      children: <Widget>[        new Row(          children: <Widget>[            new Expanded(              child: new Container(                  padding: const EdgeInsets.only(left: 5.0, top: 2.0, right: 5.0  ),                  child: new Text(label, style: infoText16BlackBold)),            ),          ],        ),        new Row(          children: <Widget>[            new Expanded(              child: new Container(                  padding: const EdgeInsets.only(left: 5.0, right: 5.0),                  child: new TextField(                      controller: textEditingController,                      decoration: new InputDecoration(hintText: adoptionHintText),                      onChanged: (String str) {                        setState(() {                          switch(label) {                            case 'Név':                              tempName = 'Név: ' + textEditingController.text + '\r\n';                              break;                            case 'Kor':                              tempAge = 'Kor: ' + textEditingController.text + '\r\n';                              break;                            case 'Cím':                              tempAddress = 'Cím: ' + textEditingController.text + '\r\n';                              break;                            default:                              break;                          }                        });                      }                  )),            ),          ],        )      ],    );  }

The problem is obviously that you will need a new TextEditingController and a new String to store every new input you want the user to enter:

  TextEditingController nameInputController = new TextEditingController();  var tempName;  TextEditingController ageInputController = new TextEditingController();  var tempAge;  TextEditingController addressInputController = new TextEditingController();  var tempAddress;

This will result in a lot of extra lines if you have a lot of fields, and you will also have to update the composeEmail() method accordingly, and the more fields you have, you will be more likely to forget a couple.

  var emailBody;  composeEmail(){    emailBody = tempName + tempAge + tempAddress;    return emailBody;  }

Finally, it is time to build the form:

@override  Widget build(BuildContext context) {    return new Scaffold(      appBar: new AppBar(        title: new Text('Örökbefogadás'),      ),      body: new ListView(        children: <Widget>[          buildTextInputRow('Név', nameInputController),          buildTextInputRow('Kor', ageInputController),          buildTextInputRow('Cím', addressInputController),          new FlatButton(onPressed: () { print(composeEmail()); }, child: new Text('test'))        ],      ),    );  }

For convenience, I just printed the e-mail body to the console while testing

I/flutter ( 9637): Név: ZoliI/flutter ( 9637): Kor: 28I/flutter ( 9637): Cím: Budapest

All this is handled in a single State.