Digit only TextFormField in Flutter

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';

An update on or after April 2021:

TextField(
   inputformatter: [
      FilteringTextInputFormatter.digitsOnly,
      ],
   textInputType: TextInputType.number,

Other examples of the use of input formatters include:

TextField(
  inputFormatters: [
    FilteringTextInputFormatter.deny(RegExp(r'[/\\]')),
  ],
)

OR

inputFormatters: [FilteringTextInputFormatter.allow(RegExp(r'^ ?\d*')),]
   inputFormatters: [FilteringTextInputFormatter.deny(' ')]

OR

Other options include:

> lowercase letters: a-z
> capital letters: A-Z
> lowercase vowels accented: á-ú
> capital vowels accented: Á-Ú
> numbers: 0-9
> space : (space)

So in the above case you can have

inputFormatters: [
        WhitelistingTextInputFormatter(RegExp("[a-z A-Z á-ú Á-Ú 0-9]"))
      ]

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