Android empty ArrayList and Spinner

Question

Hey i'm creating Android application which connect with my database MySQL. I created an ArrayList with categories and added it to Adapter and then to Spinner. I see Spinner items but after onClick nothing happens and when I try to check what is in my ArrayList I see that it is empty.Data downloaded.

After click in Spinner nothing change

Here is my code:

public class InsertProductActivity extends AppCompatActivity {
    Spinner categories;
    String categoriesURL = "myURL";
    ArrayList<String> downloadedCategories = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_insert_product);
        categories = findViewById(R.id.categories);
        getCategories();
        ArrayAdapter<String> adapter = new ArrayAdapter<>(this,android.R.layout.simple_spinner_item,downloadedCategories);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        categories.setAdapter(adapter);
    }
    protected void getCategories(){
        RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, categoriesURL
                , new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            JSONArray jsonArray = response.getJSONArray("categories");
                            for(int i=0;i<jsonArray.length();i++){
                                downloadedCategories.add(jsonArray.getJSONObject(i).getString("name"));
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
        });
        requestQueue.add(jsonObjectRequest);
    }
}

Answer 1

try this one.

protected void getCategories(){
    RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, categoriesURL, new Response.Listener<JSONObject>() {
        @Override
        public void onResponse(JSONObject response) {
            try {
                JSONArray jsonArray = response.getJSONArray("categories");
                downloadedCategories = new ArrayList<>(); // try to add your instantiation of your arrayList here.
                for(int i=0;i<jsonArray.length();i++) {
                    downloadedCategories.add(jsonArray.getJSONObject(i).getString("name"));
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {

    }
});
//this block of code will prompt after your downloadedCategories finish storing your objects to your arrayList because if you put this in onCreate this wil call before your getCategories process not finish yet. So much better its much safer here.
    ArrayAdapter<String> adapter = new ArrayAdapter<>(this,android.R.layout.simple_spinner_item,downloadedCategories);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    categories.setAdapter(adapter);
    requestQueue.add(jsonObjectRequest);
}