Allow only specific input in TextFormField without validation in Flutter

Question

I want to allow the user to only put maximum of 5 numbers between 1 and 10.000, but this TextFormField is not required and should not be submitted through Form validation, but I want to let the user know if he is adding this field, that he can not exceed 10.000 and he must put only numbers from 1 to 10.000. The code for the TextFormField:

TextFormField(
                                keyboardType: TextInputType.number,
                                controller: _number,
                                inputFormatters: <TextInputFormatter>[
                                  FilteringTextInputFormatter.digitsOnly //I have set this so the input is only numbers/digits
                                ],
                                decoration: kTextFieldDecoration.copyWith(
                                  hintText: 'Enter number between 1 and 10.000',
                                  labelText: 'Number from 1 to 10.000',
                                ),
                              ),

I'm not sure how to achieve this, I used regex validation for the rest of the fields, but since this field is not required, I can't validate it through Form validation. Any form of help is appreciated. Thanks in advance!

Solution 1

May try the code below, for your reference https://stackoverflow.com/a/68072967/7972633

Updated version 1

class NumericalRangeFormatter extends TextInputFormatter {
  final double min;
  final double max;

  NumericalRangeFormatter({required this.min, required this.max});

  @override
  TextEditingValue formatEditUpdate(
    TextEditingValue oldValue,
    TextEditingValue newValue,
  ) {

    if (newValue.text == '') {
      return newValue;
    } else if (int.parse(newValue.text) < min) {
      return TextEditingValue().copyWith(text: min.toStringAsFixed(5));
    } else {
      return int.parse(newValue.text) > max ? oldValue : newValue;
    }
  }
}

keyboardType: TextInputType.numberWithOptions(),
inputFormatters: [
   LengthLimitingTextInputFormatter(5) // only allow 5 digit number
],

Solution 2

You can use validator for a field that is not mandatory in this way :

validator: (value) {
    if (value == null || value.isEmpty) {
      return null;
    }else {
      double? num = double.tryParse(value);
      if(num == null)
         return 'Invalid value';
      else if(num < 1 || num > 10)
         return 'Please enter value between 1 and 10.000';
    }
    return null;
},

So, in this way if value is null or empty then we can skip check otherwise perform required check.

Comments

[Jahidul Islam]

you just want to put num from 1 to 10 with three decimal places and look here stackoverflow.com/questions/70059605/…

[GrandMagus]

Yes, but I still want to tell the user that he can not exceed the number 10.000, I can still put in let's say 55.000, the number limit is five but the limited number is way off.

[HeIsDying]

@GrandMagusi have updated my answer, have a try

[HeIsDying]

stackoverflow.com/questions/58836681/…

[GrandMagus]

I tested it out, it works actually, you can enter only a 5 digit number that is 10k, but any number from 1-9999 is good. Thanks for the detailed research and information provided.

[GrandMagus]

Like I said in the question above, I need this to limit the user without using validations because this field is not required in the Form populated.

[GrandMagus]

The only one more thing I need, if there is a chance to notify the user what is the limit of the input.

[Shatanik Mahanty]

Yes that's why I added a return null in case user has not filled the input for this field

[GrandMagus]

And also, please reference where to call the NumericalRangeFormatter class for people that are having the same issue (inside the inputFormatters[]). Thanks again!

[GrandMagus]

Ok, this answer is also correct, I just tested it out in multiple options and it works great, but I think I will go with @HeIsDying answer since it limits the user not to exceed those digits at start. I wish I could accept both answers to be honest! Thanks a lot mate once again!

[Shatanik Mahanty]

I also feel @HelsDying answer is much more compact and you should totally go with it. Thanks for your kind works and good luck with the work.