Restrict Special Character Input Flutter

Question

I have a TextField that will only take numbers as an input. The Keyboard that appears allows for the input of the the following characters: "-(hyphen) ,(comma) .(period) and space". How can I prevent the user from entering all except the period.

child: new TextField(
  controller: _controller,
  maxLengthEnforced: true,
  keyboardType: TextInputType.number,
  maxLength: 4, //9999 upper limit
  ), //TextField

I've tried to use RegExp to take the _controller text, remove the characters and place it back into to field without any luck.

...//Add Listener to _controller
_controller.addListener(restrictCharacters);
...

//Listener
void restrictCharacters(){
  RegExp regexp = new RegExp(
    r"^|\-|\,|\ ",
    caseSensitive: false,
    multiLine: false,);
  String text = _controller.text;
  String chng = text.replaceaLL(regExp,"");
  _controller.text = chng;
}

When applied the cursor moves to beginning and the field keeps the - (hyphen) for example.

Answer 1

In your TextInputField() include this paramenter

inputFormatters: [new WhitelistingTextInputFormatter(RegExp("[0-9]")),],

If you want to allow only letters the the Regex would be

inputFormatters: [new WhitelistingTextInputFormatter(RegExp("[a-zA-Z]")),],

Update WhitelistingTextInputFormatter has been deprecated

use FilteringTextInputFormatter like this:

TextField(
 inputFormatters: <TextInputFormatter>[
      FilteringTextInputFormatter.allow(RegExp("[0-9a-zA-Z]")),
  ], // Only numbers can be entered
),

Answer 2

WhitelistingTextInputFormatter is deprecated. You should use FilteringTextInputFormatter.allow:

inputFormatters: [ FilteringTextInputFormatter.allow(RegExp("[a-zA-Z]")), ]

or FilteringTextInputFormatter.deny instead of BlacklistingTextInputFormatter