java - 为什么我的 JsonObjectRequest 不工作？

Question

这几天我一直在摆弄这个。做错了。 Android Studio 不会让我用这个错误编译它。所以，我有这个应用程序，其中有两个选项卡和两个 fragment 。一个 fragment 称为 new，该 fragment 获取 json。但是我无法正确地做到这一点。我已经上传了错误的图片和类文件。你能帮帮我吗？

错误:“无法解析构造函数 JsonObjectRequest(int, java.lang.String, null ......)

new_fragment.java

public class new_fragment extends Fragment {
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String mParam1;
    private String mParam2;
    private VolleySingleton volleySingleton;
    private ImageLoader imageLoader;
    private RequestQueue requestQueue;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() !=null){
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
        volleySingleton = VolleySingleton.getsInstance();
        requestQueue = volleySingleton.getRequestQueue();
        RequestQueue requestQueue = VolleySingleton.getsInstance().getRequestQueue();
        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET,"http://10.0.8.152/json/new.json",null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        System.out.println(response);
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
                });
        requestQueue.add(request);
    }

    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedIntanceState) {
        setHasOptionsMenu(true);
        View layout = inflater.inflate(R.layout.new_fragment, container, false);
        return layout;
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        // TODO Auto-generated method stub
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.ref_menu, menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // handle item selection
        switch (item.getItemId()) {
            case R.id.refreshico:
                // do s.th.
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

}

Volley 单例

public class VolleySingleton {
    private static VolleySingleton sInstance = null;
    private ImageLoader mImageLoader;
    private RequestQueue mRequestQueue;
    private VolleySingleton(){
        mRequestQueue = Volley.newRequestQueue(appClass.getAppContext());
        mImageLoader = new ImageLoader(mRequestQueue,new ImageLoader.ImageCache() {
            private LruCache<String, Bitmap> cache = new LruCache<>((int)(Runtime.getRuntime().maxMemory()/1024)/8);

            @Override
            public Bitmap getBitmap(String url) {
                return cache.get(url);
            }

            @Override
            public void putBitmap(String url, Bitmap bitmap) {
                cache.put(url, bitmap);
            }
        });
    }

    public static VolleySingleton getsInstance(){
        if(sInstance==null){
            sInstance = new VolleySingleton();
        }
        return sInstance;
    }

    public RequestQueue getRequestQueue(){
        return mRequestQueue;
    }
    public ImageLoader getImageLoader(){
        return mImageLoader;
    }


}

Answer 1

强制转换 (String)null。

JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET,"http://10.0.8.152/json/new.json",(String)null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        System.out.println(response);
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {

                    }
                });