Android使用volley的一个空指针问题

Question

使用了volley的listview，但是直接停止运行。
小弟看了一天，还是不明白，问题出在哪里，求指点
错误提示：

E/AndroidRuntime: FATAL EXCEPTION: main
                                                         Process: com.xd.v2ex, PID: 32632
                                                         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.xd.v2ex/com.xd.v2ex.activity.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.xd.v2ex.utils.ApplicationController.addToRequestQueue(com.android.volley.Request)' on a null object reference
                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2702)
                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767)
                                                             at android.app.ActivityThread.access$900(ActivityThread.java:177)
                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                             at android.os.Looper.loop(Looper.java:145)
                                                             at android.app.ActivityThread.main(ActivityThread.java:5981)
                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                             at java.lang.reflect.Method.invoke(Method.java:372)
                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
                                                          Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.xd.v2ex.utils.ApplicationController.addToRequestQueue(com.android.volley.Request)' on a null object reference
                                                             at com.xd.v2ex.activity.MainActivity.fetchMovies(MainActivity.java:116)
                                                             at com.xd.v2ex.activity.MainActivity.onCreate(MainActivity.java:79)
                                                             at android.app.Activity.performCreate(Activity.java:6289)
                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2655)
                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767) 
                                                             at android.app.ActivityThread.access$900(ActivityThread.java:177) 
                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449) 
                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                             at android.os.Looper.loop(Looper.java:145) 
                                                             at android.app.ActivityThread.main(ActivityThread.java:5981) 
                                                             at java.lang.reflect.Method.invoke(Native Method) 
                                                             at java.lang.reflect.Method.invoke(Method.java:372) 
                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

MainActivity

package com.xd.v2ex.activity;

import android.app.ProgressDialog;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.util.Log;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.xd.v2ex.R;
import com.xd.v2ex.adapter.LatestAdapter;
import com.xd.v2ex.bean.ItemInfo;
import com.xd.v2ex.utils.ApplicationController;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

private static final String TAG = MainActivity.class.getSimpleName();

private ArrayList<ItemInfo> itemInfos;
private LatestAdapter latestAdapter;
private ListView latestListView;

private static final String url = "http://www.v2ex.com/api/topics/latest.json";

private ProgressDialog pDialog;

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

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    /**

• listview
  */

     latestListView = (ListView) findViewById(R.id.latestListView);
  
     itemInfos = new ArrayList<ItemInfo>();
  
     fetchMovies();
     latestAdapter = new LatestAdapter(MainActivity.this, itemInfos);
  
     latestListView.setAdapter(latestAdapter);

  }

1. void fetchMovies() {

      JsonArrayRequest req = new JsonArrayRequest(url, new Response.Listener<JSONArray>() {
   
          @Override
          public void onResponse(JSONArray jsonArray) {
   
              for (int i = 0; i < jsonArray.length(); i++) {
                  try {
                      JSONObject object=jsonArray.getJSONObject(i);
                      ItemInfo itemInfo=new ItemInfo();
                      itemInfo.setTitle(object.getString("title"));
                      itemInfo.setImage("http:"+object.getJSONObject("member").getString("avatar_large"));
                      itemInfo.setNode(object.getString("created"));
                      itemInfo.setAuthor(object.getString("id"));
   
                      itemInfos.add(itemInfo);
                  } catch (JSONException e) {
                      e.printStackTrace();
                  }
   
              }
              //ע��ˢ������
              latestAdapter.notifyDataSetChanged();
          }
      }, new Response.ErrorListener() {
          @Override
          public void onErrorResponse(VolleyError volleyError) {
              Log.e(TAG, "error:" + volleyError.getMessage());
          }
      });
      ApplicationController.getInstance().addToRequestQueue(req);

   }

   @Override

2. void onBackPressed() {

      DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
      if (drawer.isDrawerOpen(GravityCompat.START)) {
          drawer.closeDrawer(GravityCompat.START);
      } else {
          super.onBackPressed();
      }

   }

   @Override

3. boolean onCreateOptionsMenu(Menu menu) {

      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.main, menu);
      return true;

   }

   @Override

4. boolean onOptionsItemSelected(MenuItem item) {

      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.
      int id = item.getItemId();
   
      //noinspection SimplifiableIfStatement
      if (id == R.id.action_settings) {
          return true;
      }
   
      return super.onOptionsItemSelected(item);

   }

   @SuppressWarnings("StatementWithEmptyBody")
   @Override

5. boolean onNavigationItemSelected(MenuItem item) {

      // Handle navigation view item clicks here.
      int id = item.getItemId();
   
      if (id == R.id.nav_camera) {
          // Handle the camera action
      } else if (id == R.id.nav_gallery) {
   
      } else if (id == R.id.nav_slideshow) {
   
      } else if (id == R.id.nav_manage) {
   
      } else if (id == R.id.nav_share) {
   
      } else if (id == R.id.nav_send) {
   
      }
   
      DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
      drawer.closeDrawer(GravityCompat.START);
      return true;

   }
   }

Answer 1

把fetchMovies()方法调用放到latestListView.setAdapter之后

Answer 2

ApplicationController.getInstance().addToRequestQueue(req); 既然是这句报错了，你就验证下前后是否是null的，打印下ApplicationController.getInstance() 和 req 这两个，在调用前，不过看你req是在上面重新new的一个，所以ApplicationController.getInstance()这个为null的可能性比较大。

Answer 3

我快哭了…………我也是遇到这个问题，哥你是怎么解决的？？？ 跪求……