Json Array return blank (“”) when run Oncreate (android)

问题

I am trying to fetch json data from server using volley library and store in array list then display data using spinner.

my code on php server side:

echo json_encode(array('result'=>$result));

My fetch data function:

private void getEventRespondTest (RequestQueue requestQueue) {
        //Creating a string request
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST,Config.DATA_URL,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject respond) {
                            try {
                                eventArray = respond.getJSONArray("result");
                                Toast.makeText(Beacon_MainActivity.this,eventArray.toString(),Toast.LENGTH_LONG).show();
                                eventDetail = getEventDetail(eventArray);

                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
//                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                            Toast.makeText(Beacon_MainActivity.this, "Unable to fetch data: " +error.getMessage(),Toast.LENGTH_LONG).show();
                        }
                    }
                );
        //Adding request to the queue
        requestQueue.add(jsonObjectRequest);
    }

    private ArrayList getEventDetail(JSONArray j) {
        ArrayList event = new ArrayList();
        //Traversing through all the items in the json array
        for (int i = 0; i < j.length(); i++) {
            try {
                //Getting json object
                JSONObject json = j.getJSONObject(i);

                //Adding the name of the event to array list
                event.add(json.getString(Config.EVENT_TITLE));
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
        Toast.makeText(Beacon_MainActivity.this,event.toString(),Toast.LENGTH_LONG).show();
        return event;
    }

And on my OnCreate method I am trying to fetch the data and display result using spinner but when run, result return first time is blank "

eventDetail = new ArrayList<>();
        eventArray = new JSONArray();

//        //get event from server
        getEventRespondTest(Volley.newRequestQueue(Beacon_MainActivity.this));
        spinner.setAdapter(new ArrayAdapter<>(Beacon_MainActivity.this, android.R.layout.simple_spinner_dropdown_item, eventDetail));

Any help is much appreciate. Thanks.

回答1:

Your function private void getEventRespondTest is returning null as it is Void. What are you doing with eventDetail = getEventDetail(eventArray); getEventRespondTest function? Or tried to change POST to GET?

UPDATE CHECK THIS CODE

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        getEventRespondTest();
    }


 private void getEventRespondTest () {
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        StringRequest request = new StringRequest("http://vinhvumobile.com/phpconnect/geteventdetail.php", new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                // we got the response, now our job is to handle it
                getDataFromJson(response);
            }
        }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                //something happened, treat the error.
                Log.e("Error", error.toString());
            }
        });
        queue.add(request);
    }

    private ArrayList getDataFromJson(String json) {
        ArrayList events=new ArrayList();
        JSONArray array;
        try {

            JSONObject gallery=new JSONObject(json);
            array=gallery.getJSONArray("result");
            //Do sth with it

            for(int i=0;i<array.length();i++){
                JSONObject jsonOBJ = (JSONObject) array.get(i);
                events.add(jsonOBJ.get("EventID"));
            }

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

回答2:

I think you response in method public void onResponse(JSONObject respond) respond is null because you use JsonObjectRequest to make request but your server(php) return a String it mean nothing JsonObject to return. Try use StringRequest instead of JsonObjectRequest . In best solution is change code your server for it return a `JsonObject' follow this (php file):

header('Content-Type: application/json');
echo json_encode(array('result'=>$result), 256); // 256 for UTF-8 data

来源：https://stackoverflow.com/questions/33991227/json-array-return-blank-when-run-oncreate-android