Digit only TextFormField in Flutter

Question

Im am working on an app that requires a price input in ¥ and as such has no decimal places. If we use keyboardType: TextInputType.numberWithOptions() we can get a number pad input. If we use validator: (input) { } we can check if input is valid but we cannot prevent it.

The problem is we can save a draft that will not need validation. So it is better for us to only allow digit input in the first place.

import 'package:flutter/material.dart';  void main() => runApp(MyApp());  class MyApp extends StatelessWidget {   @override   Widget build(BuildContext context) {     return MaterialApp(       title: 'Digits Only',       theme: ThemeData(         primarySwatch: Colors.blue,       ),       home: MyHomePage(title: 'Flutter Demo Home Page'),     );   } }  class MyHomePage extends StatefulWidget {   MyHomePage({Key key, this.title}) : super(key: key);    final String title;    @override   _MyHomePageState createState() => new _MyHomePageState(); }  class _MyHomePageState extends State<MyHomePage> {   @override   Widget build(BuildContext context) {     return Scaffold(       appBar: AppBar(         title: Text(widget.title),       ),       body: Center(         child: Column(           mainAxisAlignment: MainAxisAlignment.center,           children: [             TextFormField(               autovalidate: true,               keyboardType: TextInputType.number,               validator: (input) {                 final isDigitsOnly = int.tryParse(input);                 return isDigitsOnly == null                     ? 'Input needs to be digits only'                     : null;               },             ),           ],         ),       ),     );   } } 

Is there a way to prevent certain text input and only allow digits?

Answer 1

Yep, you can use the inputFormatters attribute and add the WhitelistingTextInputFormatter.digitsOnly expression

  import 'package:flutter/services.dart';     TextFormField(           ...           inputFormatters: [WhitelistingTextInputFormatter.digitsOnly],         ) 

You can find more info here: https://docs.flutter.io/flutter/services/TextInputFormatter-class.html

After flutter 1.12, WhitelistingTextInputFormatter was deprecated and you are running a newer version, use :

FilteringTextInputFormatter.digitsOnly

https://api.flutter.dev/flutter/services/FilteringTextInputFormatter-class.html

Answer 2

With WhitelistingTextInputFormatter deprecated and using a double number:

keyboardType: TextInputType.numberWithOptions(decimal: true), inputFormatters: [FilteringTextInputFormatter.allow(RegExp('[0-9.,]+')),], onChanged: (value) => doubleVar = double.parse(value), 

RegExp('[0-9.,]+') allows for digits between 0 and 9, also comma and dot.

You can use RegExp('([0-9]+(\.[0-9]+)?)') to allow digits and only one dot. See explanation here.

double.parse() converts from string to double.

Don't forget you need: import 'package:flutter/services.dart';