how to limit the user to enter number outside the given range(says 1 to 4000) in flutter textformfield

Question

Restricts the user's input. For example, if I set the numeric limit to 4000, the user cannot enter a number greater than 4000.

TextFormField(
                //TODO:보유수량 이상 쓰는것 방지할것.
                controller: _recruitStockEditingController,
                keyboardType: TextInputType.number,
                inputFormatters: [FilteringTextInputFormatter.digitsOnly],
                decoration: InputDecoration(
                    contentPadding: EdgeInsets.only(
                        left: 21.0.w, top: 11.0.h, bottom: 11.0.h),
                    hintText: "수량을 입력해주세요.",
                    hintStyle: TextStyle(
                        fontSize: 14.0.sp, color: const Color(0xff696C75)),
                    border: OutlineInputBorder(
                        borderSide: const BorderSide(color: Color(0xffCACBD4)),
                        borderRadius: BorderRadius.circular(6))),
              ),

Answer 1

1. Try this with TextInputFormatter

   import 'package:flutter/services.dart';

    class NumberLimitFormatter extends TextInputFormatter {
      @override
      TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
        if(newValue.text == "") return newValue;
        if(int.parse(newValue.text.toString())<4000){
          return newValue;
        }
        return oldValue;
      }
    }
   

Uasge:

TextField(
              controller: myController,
                keyboardType: TextInputType.number,
                inputFormatters: [
                  NumberLimitFormatter(),
                  FilteringTextInputFormatter.digitsOnly,
                 ],
            ),

2. Using Validator and TextFormField:

 TextFormField(
        keyboardType: TextInputType.number,
        autovalidateMode: AutovalidateMode
            .onUserInteraction, // to instantly valid the input
        inputFormatters: [
          FilteringTextInputFormatter.digitsOnly,
        ],
        validator: (String? value) {
          if (value == null || value.isEmpty)
            return "Enter number";
          else if (int.parse(value) > 4000)
            return "Entered number can't be greater than 4000";
          else
            return null;
        }),