flutter textformfield issue

  if (isPraticeChecked)
                TextFormField(
                    decoration:
                        const InputDecoration(labelText: 'No.of Questions'),
                    controller: noOfquestionController,
                    keyboardType: TextInputType.number,
                    inputFormatters: [
                      FilteringTextInputFormatter.digitsOnly
                    ],
                    validator: (value) {
                      final isNum = num.tryParse(value!);
                      
                      if (isNum == null ||
                          int.parse(value) < 1 ||
                          int.parse(value) > 30) {
                        return 'No. of question must be 1 to 30.';
                      }
                      return null;

this is the textformfield keyboardtype.number this kb only receiving num if user enter other then num like "-",",",".," it is giving blank page