Flutter - update form state from validator - dart

Question

I have a form with some inputs. I am using a GlobalKey<FormState> to handle submissions and validation and so on.
One of the fields is supposed to take a double input, so I validate that by trying to parse the input value to double like so :
return TextFormField(
decoration: InputDecoration(labelText: 'Price'),
keyboardType: TextInputType.number,
validator: (String value) {
double _parsedValue = double.tryParse(value);
if (_parsedValue == null) {
return "Please input a number";
}
},
onSaved: (String value) {
setState(() {
_price = double.parse(value);
});
},
);
Now that works as expected. However, if the user inputs for example 9,99 that would fail, because the parse expects 9.99 .
What I'm trying to do is, when the validator is called, I'd like to check the input string for any commas, and then if they are present, replace them with dots instead, and update the form value accordingly.
My question is - can we actually update the form state from within validators?

Answer 1

I think maybe what you need is a TextInputFormatter.
Here is a link to the docs https://docs.flutter.io/flutter/services/TextInputFormatter-class.html
There are pre-existing formatters you can use as a reference to convert comma's to dots.

Answer 2

I don't think you need to update the state in the validator. I would use only the save event to update the state. This way it gets very clear where the state is updated.
I believe nothing forbids you to update the state in the validate, but maybe it would get less organized. :)
Solution that do not exactly answer your question
I guess the best way to accomplish what you need would be using a TextInputFormatter with a WhitelistingTextInputFormatter, check it out:
Note the TextInputType.numberWithOptions(decimal: true) and that if the user pastes "-100,00" , it would become 100.0 - which for a price would be fine, but not for double values in general.
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'ValidatorState',
theme: ThemeData(primarySwatch: Colors.yellow),
home: MyFormPage(),
);
}
}
class MyFormPage extends StatefulWidget {
#override
_MyFormPageState createState() => _MyFormPageState();
}
class _MyFormPageState extends State<MyFormPage> {
final _formKey = GlobalKey<FormState>();
double _price;
void _save() {
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
Scaffold.of(_formKey.currentContext)
.showSnackBar(SnackBar(content: Text('New price defined! ($_price)')));
}
}
Widget _buildForm(BuildContext context) {
return Container(
padding: EdgeInsets.all(10.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
TextFormField(
inputFormatters: <TextInputFormatter>[
WhitelistingTextInputFormatter(RegExp("[0-9.]"))
],
decoration: InputDecoration(labelText: 'Price'),
keyboardType: TextInputType.numberWithOptions(decimal: true),
validator: (String value) {
double _parsedValue = double.tryParse(value);
if (_parsedValue == null) {
return "Please input a valid number";
}
if (_parsedValue == 0.0) {
return "Please input a valid price";
}
},
onSaved: (String value) {
setState(() {
_price = double.tryParse(value);
});
},
),
Text(""),
RaisedButton(
child: Text("Save"),
color: Theme.of(context).primaryColor,
textColor: Theme.of(context).primaryTextTheme.title.color,
onPressed: _save,
),
Text(""),
TextFormField(
decoration: InputDecoration(labelText: 'Copy and Paste area'),
),
],
),
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Validator State"),
),
body: Form(
key:_formKey,
child: _buildForm(context),
),
);
}
}
Solution that answers your question
However, that is not exactly what you described. You want to automatically replace , to .. I would avoid doing that, as 1,234.56 would translate to 1.234.56, which is invalid. If you only strip out the commas, you end up with 1234.56 which is valid.
If you really want to do as you said, you have to use a TextEditingController and a function to normalize the text data. I've made the example below, check it out - specially the _priceController and the _parsePrice.
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'ValidatorState',
theme: ThemeData(primarySwatch: Colors.yellow),
home: MyFormPage(),
);
}
}
class MyFormPage extends StatefulWidget {
#override
_MyFormPageState createState() => _MyFormPageState();
}
class _MyFormPageState extends State<MyFormPage> {
final _formKey = GlobalKey<FormState>();
TextEditingController _priceController;
double _price;
#override
void initState() {
super.initState();
_priceController = TextEditingController();
}
#override
void dispose() {
_priceController?.dispose();
super.dispose();
}
void _save() {
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
Scaffold.of(_formKey.currentContext)
.showSnackBar(SnackBar(content: Text('New price defined! ($_price)')));
}
}
double _parsePrice(String text) {
var buffer = new StringBuffer();
text.runes.forEach((int rune) {
// acceptable runes are . or 0123456789
if (rune == 46 || (rune >= 48 && rune <= 57)) buffer.writeCharCode(rune);
// if we find a , we replace with a .
if (rune == 44) buffer.writeCharCode(46);
});
return double.tryParse(buffer.toString());
}
Widget _buildForm(BuildContext context) {
return Container(
padding: EdgeInsets.all(10.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
TextFormField(
controller: _priceController,
decoration: InputDecoration(labelText: 'Price'),
keyboardType: TextInputType.numberWithOptions(decimal: true),
validator: (String value) {
double _parsedValue = _parsePrice(value);
if (_parsedValue == null) {
return "Please input a valid number";
}
if (_parsedValue == 0.0) {
return "Please input a valid price";
}
},
onSaved: (String value) {
setState(() {
_price = _parsePrice(value);
_priceController.text = _price.toString();
});
},
),
Text(""),
RaisedButton(
child: Text("Save"),
color: Theme.of(context).primaryColor,
textColor: Theme.of(context).primaryTextTheme.title.color,
onPressed: _save,
),
],
),
);
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Validator State"),
),
body: Form(
key:_formKey,
child: _buildForm(context),
),
);
}
}

Answer 3

hi did you get a fix for this?
I would rethink your strategy for this issue.
Maybe what you need is an observer function that is triggered when the user typing, which then looks at the comma and changes it to a dot.
TextFormField has a built in function,
onEditingCompleted and onFieldSubmitted which can run the function you have to make the check before the validate is run.