[英]add(com.android.volley.Request<java.lang.Object>) in RequestQueue cannot be aplied to (com.example.nikochan.instaticket.CrearEventoRequest)
[英]I keep getting com.android.volley.RequestQueue.add on a null object reference error
我需要顯示一個JSON文件中的產品列表,但我不斷收到此錯誤:
https://i.imgur.com/WEu4DzV.png
我嘗試移動代碼中的所有內容(因此可能將其弄亂了一點),但我無法使其正常工作。 我是一個初學者,因此很難為我解決此類錯誤。
這是產生錯誤的片段:
package com.example.app;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public class ListFragment extends Fragment {
private RecyclerView mRecyclerView;
private ListAdapter mListAdapter;
private ArrayList<Item> mList;
private RequestQueue mRequestQueue;
Context context;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_list, container, false);
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mRecyclerView = view.findViewById(R.id.recycler_view);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
mRecyclerView.setAdapter(mListAdapter);
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
parseJSON();
super.onActivityCreated(savedInstanceState);
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mList = new ArrayList<>();
mListAdapter = new ListAdapter(context, mList);
}
private void parseJSON() {
String url = "http://my_ip_adress/sestavsisvujsvetweb/api/seznammagnetek";
JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
int number = 0;
try {
number = response.getInt("monumentid1");
} catch (JSONException e) {
e.printStackTrace();
}
String name = null;
try {
name = response.getString("name1");
} catch (JSONException e) {
e.printStackTrace();
}
String region = null;
try {
region = response.getString("region1");
} catch (JSONException e) {
e.printStackTrace();
}
mRequestQueue = Volley.newRequestQueue(context);
mList.add(new Item(number, name, region));
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
mRequestQueue.add(request); //this causes the problem, why? :(
}
}
發生此問題的原因是您在試圖將請求添加到requestQueue之前,先知道該請求已成功檢索了您的信息。 首先,檢查JsonObjectRequest是否具有onSuccess函數,如果沒有,則需要在onResponse內部添加到requestQueue。 否則,android是同步的,因此它將在實際檢索Json之前執行您的代碼行。
因此,快速的解決方法是:
if(request != null) {
mRequestQueue.add(request);
}
如果它為null,將確保不添加。 將此添加到您的onCreate中:
mRequestQueue = Volley.newRequestQueue(context);
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