我正在尝试从ListView中的URL解析JSON，但它显示错误
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.toolbox.ImageLoader com.example.vijaypremi.acmeoopsfood.util.AppController.getImageLoader()' on a null object reference
at com.example.vijaypremi.acmeoopsfood.adapter.CustomListAdapter.<init>(CustomListAdapter.java:26)
at com.example.vijaypremi.acmeoopsfood.MainActivity.onCreate(MainActivity.java:44)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
我的主要活动是：
public class MainActivity extends Activity {
// Log tag
private static final String TAG = MainActivity.class.getSimpleName();
// Billionaires json url
private static final String url = "http://ibookstay.com/oops/restapi/all-restaurant";
private ProgressDialog pDialog;
private List<RestaurentInfo> RestaurentInfoList = new ArrayList<RestaurentInfo>();
private ListView listView;
private CustomListAdapter adapter;
String in;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.list);
adapter = new CustomListAdapter(this, RestaurentInfoList);
listView.setAdapter(adapter);
pDialog = new ProgressDialog(this);
// Showing progress dialog before making http request
pDialog.setMessage("Loading...");
pDialog.show();
// Creating volley request obj
final JsonArrayRequest reqqueue = new JsonArrayRequest(url,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
hidePDialog();
// Parsing json
try {
JSONObject jsonRootObject = new JSONObject(url);
//Get the instance of JSONArray that contains JSONObjects
JSONArray mainnode =jsonRootObject.getJSONArray("data");
//Iterate the jsonArray and print the info of JSONObjects
for(int i=0; i < mainnode.length(); i++){
JSONObject jsonObject = mainnode.getJSONObject(i);
JSONObject data = jsonObject.getJSONObject("restaurentInfo");
RestaurentInfo restaurentinfo = new RestaurentInfo();
restaurentinfo.setRestaurent_name(data.getString("restaurent_name"));
restaurentinfo.setRestaurent_logo(data.getString("restaurent_logo"));
restaurentinfo.setRestaurent_phone_number(data.getString("restaurent_phone_number"));
restaurentinfo.setRestaurent_bussiness_owner_name(data.getString("restaurent_bussiness_owner_name"));
restaurentinfo.setRestaurent_email(data.getString("restaurent_email"));
}
Log.d(TAG, "onResponse: ");
} catch (JSONException e) {e.printStackTrace();}
// notifying list adapter about data changes
// so that it renders the list view with updated data
adapter.notifyDataSetChanged();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "Error: " + error.getMessage());
hidePDialog();
}
});
// Adding request to request queue
AppController.getInstance().addToRequestQueue(reqqueue);
}
@Override
public void onDestroy() {
super.onDestroy();
hidePDialog();
}
private void hidePDialog() {
if (pDialog != null) {
pDialog.dismiss();
pDialog = null;
}
}
}
我的CustomListAdapter是：
public class CustomListAdapter extends BaseAdapter {
private Activity activity;
private LayoutInflater inflater;
private List<RestaurentInfo> restaurentinfo;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();
public CustomListAdapter(Activity activity, List<RestaurentInfo> restaurentinfo) {
this.activity = activity;
this.restaurentinfo = restaurentinfo;
}
@Override
public int getCount() {
return restaurentinfo.size();
}
@Override
public Object getItem(int location) {
return restaurentinfo.get(location);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (inflater == null)
inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.list_row, null);
if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();
NetworkImageView thumbNail = (NetworkImageView) convertView
.findViewById(R.id.thumbnail);
TextView name = (TextView) convertView.findViewById(R.id.name);
TextView worth = (TextView) convertView.findViewById(R.id.worth);
TextView source = (TextView) convertView.findViewById(R.id.source);
TextView year = (TextView) convertView.findViewById(R.id.inYear);
// getting billionaires data for the row
RestaurentInfo m = restaurentinfo.get(position);
// thumbnail image
thumbNail.setImageUrl(m.getRestaurent_logo(), imageLoader);
// name
name.setText(m.getRestaurent_name());
// Wealth Source
source.setText("Wealth Source: " + String.valueOf(m.getRestaurent_info_id()));
worth.setText(String.valueOf(m.getRestaurent_phone_number()));
// release year
year.setText(String.valueOf(m.getRestaurent_email()));
return convertView;
}
}
对于Request Queue和Image Loader，我创建了AppController：
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public ImageLoader getImageLoader() {
getRequestQueue();
if (mImageLoader == null) {
mImageLoader = new ImageLoader(this.mRequestQueue,
new LruBitmapCache());
}
return this.mImageLoader;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
// set the default tag if tag is empty
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
答案 0 :(得分：0)
您的请求对象可能会检索数据 - 但您不会在onResponse覆盖中使用它。
这需要使用响应。
// Creating volley request obj
final JsonArrayRequest reqqueue = new JsonArrayRequest(url,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
hidePDialog();
// Parsing json
try {
/*** you wanna use the response here... ***/
JSONObject jsonRootObject = new JSONObject(url);
//Get the instance of JSONArray that contains JSONObjects
JSONArray mainnode =jsonRootObject.getJSONArray("data");
//Iterate the jsonArray and print the info of JSONObjects
for(int i=0; i < mainnode.length(); i++){
JSONObject jsonObject = mainnode.getJSONObject(i);
JSONObject data = jsonObject.getJSONObject("restaurentInfo");
RestaurentInfo restaurentinfo = new RestaurentInfo();
restaurentinfo.setRestaurent_name(data.getString("re
答案 1 :(得分：0)
首先，您需要在清单
中声明该类<application
android:name=".AppController"
然后，看看这是否有效。您需要在另一个实例中获取实例。
public class CustomListAdapter extends BaseAdapter {
.......
ImageLoader imageLoader;
public CustomListAdapter(Activity activity, List<RestaurentInfo> restaurentinfo) {
this.activity = activity;
this.restaurentinfo = restaurentinfo;
this.imageLoader = AppController.getInstance().getImageLoader();
}