private void readGrades() {
        managerAdminApi.grade(new Callback<String>() {
            @Override
            public void onResponse(@NonNull Call<String> call, @NonNull Response<String> response) {
                try {
                    JSONObject obj = new JSONObject(String.valueOf(response));
                    if(obj.optString("success").equals("true")) {
                        gradeList = new ArrayList<>();
                        JSONArray dataArray = obj.getJSONArray("data");
                        for (int i=0; i < dataArray.length(); i++) {
                            ObjectGrade gradeSpinner = new ObjectGrade();
                            JSONObject dataObj = dataArray.getJSONObject(i);
                            gradeSpinner.setId(dataObj.getInt("id"));
                            gradeSpinner.setGrade(dataObj.getString("grade"));
                            gradeList.add(gradeSpinner);
                        }
                        for (int i = 0; i < gradeList.size(); i++){
                            gradeNames.add(gradeList.get(i).getGrade());
                        }
                        ArrayAdapter<String> gradeArrayAdapter = new ArrayAdapter<String> (Objects.requireNonNull(getActivity()), simple_spinner_item, gradeNames);
                        gradeArrayAdapter.setDropDownViewResource(android.R.layout.simple_selectable_list_item);
                        gradeSpinner.setAdapter(gradeArrayAdapter);

                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            }

            @Override
            public void onFailure(Call<String> call, Throwable t) {

            }
        });
    }