How to properly use GetX with TextField and some server side validation?

I'm using get package for my project's state management. But i'm confused by the implementation for form inputs and validation since i couldn't find any example for it in the documentation. I have some questions regarding to this issue.

1. Should i create separate controller for each action? like PageOneController and PageOneFormController?
2. How to prevent the parent from rebuilding the child when the state changes?
3. How to trigger rebuild on data addition inside the Model().obs object?

As I mentioned above at point number 1, i found that using separate controller is a bit repetitive and unnecessary, but using same controller at multiple places prevents me to reset the state when i leave the child page since the controller was only destroyed when I leave the page which has initialized the state. To prevent any confusion from my explanation, please have a look at the illustration below.

At point number 2, as we know that the TextField widget accepts errorText for displaying an error message which is only accept a string. With this package in mind, when I try to change state of the error by the onChanged: (value) {} event, it rebuilds the entire widget everytime i type a value inside it which causing the input indicator stayed at the beginning.

In this case, point number 2 is no more happened but now it won't update the error state at all and it keep showing the error message, even when i typed a new value onto it.

Please help, here is my script:

education_info_create_page.dart

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:prismahrfinal/app/controllers/account_info/education_info_controller.dart';
import 'package:prismahrfinal/app/ui/widgets/form_input.dart';

class EducationInfoCreatePage extends GetWidget<EducationInfoController> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            title: Text('Add Education Info'),
            floating: true,
          ),
          SliverToBoxAdapter(
            child: Padding(
              padding: const EdgeInsets.symmetric(vertical: 30, horizontal: 20),
              child: Column(
                children: <Widget>[
                  Obx(
                    () => FormInput(
                      autofocus: true,
                      label: 'Institution name',
                      focusNode: controller.institutionFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.institutionError,
                      onChanged: (value) {
                        controller.institutionError = null;
                        controller.institution = value;
                      },
                      onSubmitted: (_) {
                        controller.graduationMonthFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Graduation month',
                      focusNode: controller.graduationMonthFN,
                      keyboardType: TextInputType.number,
                      textInputAction: TextInputAction.next,
                      errorText: controller.graduationMonthError,
                      onChanged: (value) {
                        controller.graduationMonthError = null;
                        controller.graduationMonth = int.parse(value);
                      },
                      onSubmitted: (_) {
                        controller.graduationYearFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Graduation Year',
                      focusNode: controller.graduationYearFN,
                      keyboardType: TextInputType.number,
                      textInputAction: TextInputAction.next,
                      errorText: controller.graduationYearError,
                      onChanged: (value) {
                        controller.graduationYearError = null;
                        controller.graduationYear = int.parse(value);
                      },
                      onSubmitted: (_) {
                        controller.qualificationFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Qualification',
                      focusNode: controller.qualificationFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.qualificationError,
                      onChanged: (value) {
                        controller.qualificationError = null;
                        controller.qualification = value;
                      },
                      onSubmitted: (_) {
                        controller.locationFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Location',
                      focusNode: controller.locationFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.locationError,
                      onChanged: (value) {
                        controller.locationError = null;
                        controller.location = value;
                      },
                      onSubmitted: (_) {
                        controller.fieldOfStudyFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Field of study',
                      focusNode: controller.fieldOfStudyFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.fieldOfStudyError,
                      onChanged: (value) {
                        controller.fieldOfStudyError = null;
                        controller.fieldOfStudy = value;
                      },
                      onSubmitted: (_) {
                        controller.majorsFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Majors',
                      focusNode: controller.majorsFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.majorsError,
                      onChanged: (value) {
                        controller.majorsError = null;
                        controller.majors = value;
                      },
                      onSubmitted: (_) {
                        controller.finalScoreFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Final Score',
                      focusNode: controller.finalScoreFN,
                      keyboardType: TextInputType.text,
                      textInputAction: TextInputAction.next,
                      errorText: controller.finalScoreError,
                      onChanged: (value) {
                        controller.finalScoreError = null;
                        controller.finalScore = double.parse(value);
                      },
                      onSubmitted: (_) {
                        controller.additionalInfoFN.requestFocus();
                      },
                    ),
                  ),
                  Obx(
                    () => FormInput(
                      label: 'Additional Info (optional)',
                      focusNode: controller.additionalInfoFN,
                      keyboardType: TextInputType.multiline,
                      maxLines: 5,
                      textInputAction: TextInputAction.go,
                      errorText: controller.additionalInfoError,
                      onChanged: (value) {
                        controller.additionalInfoError = null;
                        controller.additionalInfo = value;
                      },
                      onSubmitted: (_) {
                        controller.add();
                      },
                    ),
                  ),
                ],
              ),
            ),
          ),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.send, color: Colors.white),
        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(20)),
        backgroundColor: Theme.of(context).primaryColor,
        tooltip: 'Add Education Info',
        onPressed: controller.add,
      ),
    );
  }
}

education_info_controller.dart

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:meta/meta.dart';
import 'package:pretty_json/pretty_json.dart';
import 'package:prismahrfinal/app/data/models/account_info/education_info.dart';
import 'package:prismahrfinal/app/data/models/account_info/education_info_error.dart';
import 'package:prismahrfinal/app/data/repositories/account_info/education_info_repository.dart';

class EducationInfoController extends GetxController {
  EducationInfoController({@required this.repository})
      : assert(repository != null);

  final EducationInfoRepository repository;
  final FocusNode _institutionFN = FocusNode();
  final FocusNode _graduationMonthFN = FocusNode();
  final FocusNode _graduationYearFN = FocusNode();
  final FocusNode _qualificationFN = FocusNode();
  final FocusNode _locationFN = FocusNode();
  final FocusNode _fieldOfStudyFN = FocusNode();
  final FocusNode _majorsFN = FocusNode();
  final FocusNode _finalScoreFN = FocusNode();
  final FocusNode _additionalInfoFN = FocusNode();

  final Rx<ListEducationInfo> data = ListEducationInfo().obs;
  final Rx<EducationInfo> education = EducationInfo().obs;
  final Rx<EducationInfoError> errors = EducationInfoError().obs;

  @override
  void onInit() => fetchDataFromApi();

  void fetchDataFromApi() async {
    data.value = await repository.getData();
    if (data.value == null) {
      Get.snackbar("Error", "Can't connect to server");
    }
  }

  void add() async {
    this._unfocus();
    debugPrint(prettyJson(education.value.toJson()));

    final response = await repository.add(education.value.toJson());
    if (response == null) {
      Get.snackbar("Error", "Can't connect to server");
      return;
    } else if (response is EducationInfoError) {
      errors.value = response;
      return;
    }

    data.value.educations.add(response);
  }

  void _unfocus() {
    this.institutionFN.unfocus();
    this.graduationMonthFN.unfocus();
    this.graduationYearFN.unfocus();
    this.qualificationFN.unfocus();
    this.locationFN.unfocus();
    this.fieldOfStudyFN.unfocus();
    this.majorsFN.unfocus();
    this.finalScoreFN.unfocus();
    this.additionalInfoFN.unfocus();
  }

  // Getters -- Focus Nodes
  get institutionFN => this._institutionFN;
  get graduationMonthFN => this._graduationMonthFN;
  get graduationYearFN => this._graduationYearFN;
  get qualificationFN => this._qualificationFN;
  get locationFN => this._locationFN;
  get fieldOfStudyFN => this._fieldOfStudyFN;
  get majorsFN => this._majorsFN;
  get finalScoreFN => this._finalScoreFN;
  get additionalInfoFN => this._additionalInfoFN;

  // Getters -- Values
  get institution => this.education.value.institution;
  get graduationMonth => this.education.value.graduationMonth;
  get graduationYear => this.education.value.graduationYear;
  get qualification => this.education.value.qualification;
  get location => this.education.value.location;
  get fieldOfStudy => this.education.value.fieldOfStudy;
  get majors => this.education.value.majors;
  get finalScore => this.education.value.finalScore;
  get additionalInfo => this.education.value.additionalInfo;

  // Getters -- Errors
  get institutionError => this.errors.value.institution?.first;
  get graduationMonthError => this.errors.value.graduationMonth?.first;
  get graduationYearError => this.errors.value.graduationYear?.first;
  get qualificationError => this.errors.value.qualification?.first;
  get locationError => this.errors.value.location?.first;
  get fieldOfStudyError => this.errors.value.fieldOfStudy?.first;
  get majorsError => this.errors.value.majors?.first;
  get finalScoreError => this.errors.value.finalScore?.first;
  get additionalInfoError => this.errors.value.additionalInfo?.first;

  // Setters -- Values
  set institution(value) => this.education.value.institution = value;
  set graduationMonth(value) => this.education.value.graduationMonth = value;
  set graduationYear(value) => this.education.value.graduationYear = value;
  set qualification(value) => this.education.value.qualification = value;
  set location(value) => this.education.value.location = value;
  set fieldOfStudy(value) => this.education.value.fieldOfStudy = value;
  set majors(value) => this.education.value.majors = value;
  set finalScore(value) => this.education.value.finalScore = value;
  set additionalInfo(value) => this.education.value.additionalInfo = value;

  // Setters -- Errors
  set institutionError(value) => this.errors.value.institution = value;
  set graduationMonthError(value) => this.errors.value.graduationMonth = value;
  set graduationYearError(value) => this.errors.value.graduationYear = value;
  set qualificationError(value) => this.errors.value.qualification = value;
  set locationError(value) => this.errors.value.location = value;
  set fieldOfStudyError(value) => this.errors.value.fieldOfStudy = value;
  set majorsError(value) => this.errors.value.majors = value;
  set finalScoreError(value) => this.errors.value.finalScore = value;
  set additionalInfoError(value) => this.errors.value.additionalInfo = value;
}

app_pages.dart

import 'package:get/get.dart';
import 'package:prismahrfinal/app/bindings/education_info_binding.dart';
import 'package:prismahrfinal/app/bindings/employment_info_binding.dart';
import 'package:prismahrfinal/app/bindings/personal_info_binding.dart';
import 'package:prismahrfinal/app/ui/android/account_info/education_info/education_info.dart';
import 'package:prismahrfinal/app/ui/android/account_info/education_info/education_info_create.dart';
import 'package:prismahrfinal/app/ui/android/account_info/employment_info/employment_info.dart';
import 'package:prismahrfinal/app/ui/android/account_info/personal_info/personal_info.dart';
import 'package:prismahrfinal/app/ui/android/account_info/personal_info/personal_info_edit.dart';
import 'package:prismahrfinal/app/ui/android/home.dart';
import 'package:prismahrfinal/app/ui/android/login.dart';
import 'package:prismahrfinal/app/ui/android/account_info.dart';
part './app_routes.dart';

abstract class AppPages {
  static final pages = [
    GetPage(
      name: Routes.EDUCATION_INFO,
      page: () => EducationInfoPage(),
      binding: EducationInfoBinding(),
    ),
    GetPage(
      name: Routes.EDUCATION_INFO_CREATE,
      page: () => EducationInfoCreatePage(),
    ),
  ];
}