执行JsonObjectRequest时遇到困难

Question

在实现JsonObjectRequest时，我很难从网络上获得JsonObject。我正在尝试创建一个新的JsonObjectRequest：

  JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {

                        JSONObject ratesJsonObj = response.getJSONObject("rates");
                        String RON = ratesJsonObj.getString("RON");

                        Log.v("Currency", RON);

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

                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    });

但是所有的一切都是被安卓工作室用红色装饰的，上面写着

Error:(41, 47) error: reference to JsonObjectRequest is ambiguous, both constructor 
JsonObjectRequest(int,String,String,Listener<JSONObject>,ErrorListener)
in JsonObjectRequest and constructor 
JsonObjectRequest(int,String,JSONObject,Listener<JSONObject>,ErrorListener) 
in JsonObjectRequest match

有人知道怎么回事吗？

Answer 1

试着这样做：

JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, (JSONObject) null,
        new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                try {

                    JSONObject ratesJsonObj = response.getJSONObject("rates");
                    String RON = ratesJsonObj.getString("RON");

                    Log.v("Currency", RON);

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

            }
        }, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {

    }
});

Answer 2

将null转换为string，它将工作。(字符串)空