How to determine spinner string array list item when a radio button is selected in android?

Question

I'm confused about how to determine the array for my spinner based on the selected radio button.

So I have 1 spinner and 1 RadioButtonGroup contain with 2 RadioButtons. My case is like :

1. If RadioButton_A is selected then the spinner will display this list :

<string-array name="spinner_item_a">
    <item>plant 1</item>
    <item>plant 2</item>
    <item>plant 3</item>
</string-array>

2. If RadioButton_A is selected then the spinner will display this list :

 <string-array name="spinner_item_b">
    <item>fruit 1</item>
    <item>fruit 2</item>
    <item>fruit 3</item>
</string-array>

I'm using SharedPreferences to pass the value of the RadioButton so that the spinner can get the value. Here's my code for selected RadioButton :

onSelectedChapterChange = new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                chapters = group.getCheckedRadioButtonId() == R.id.chapter_1_radio_button ? plant : fruit;
                if (chapters.equals(plant))
                    setPrefType = "Plant";
                if (nationality.equals(fruit))
                    setPrefType = "Fruit";
                    SharedPreferences.Editor sPref = context.getSharedPreferences("ChapterTypePref", Context.MODE_PRIVATE).edit();
                    sPref.putString("ChapterInfo",setPrefType);
                    sPref.apply();
            }
        };

Here's my listener for spinner :

chapterSelectedListener = new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) 
             {
            if (position > 0) {
                chapterType = chapterItemValueList.get(position-1);
            }
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    };

Here's how I set the list of item into the adapter :

 private void initChapterSpinner(final Context context, Resources resources) {
        SharedPreferences pref = context.getSharedPreferences("ChapterTypePref", Context.MODE_PRIVATE);
        String chapterPref = pref.getString("ChapterInfo","");
        if (chapterPref == "Plant"){
            chapterItemValueList = new ArrayList<>(Arrays.asList(
                resources.getStringArray(R.array.spinner_item_a)));
        } else if (chapterPref == "Fruit"){
            chapterItemValueList = new ArrayList<>(Arrays.asList(
                resources.getStringArray(R.array.spinner_item_b)));
        }
        
        idTypeArrayAdapter = new IdTypeSpinnerAdapter(context, idTypeItemValueList);

        idTypeArrayAdapter.setDropDownViewResource(R.layout.spinner_dropdown_cdd);
    }

It turns out that, the list item of the spinner adapter becomes null. I already got the logic on how's the flow should be run, but it's just confusing on implementing it. Please kindly help me, Thank you :D