我正在尝试检索 Foursquare 场地列表。我有一个异步类来解析 Json，另一个来创建和显示列表。但我有一些错误，如解析错误、nullpointerexception..而且我不知道如何解决这个问题。我要解析的 Json 来自foursquare url。例如https://api.foursquare.com/v2/venues/search?ll=40.7,-74&radius=0&client_id=50QO00GZKUPA25PDGO1IY3UHMK3IBEMO2F4CTO5M2DBLVGQD&client_secret=MVJZGC3WT4V55DQPJYBFNZ5X3IACIDLFVM1HKA2WBTEHAXDF&v=201
这是logCat
07-24 12:39:06.485: E/SensorManager(19711): thread start
07-24 12:39:06.495: D/SensorManager(19711): registerListener :: handle = 0 name= K3DH Acceleration Sensor delay= 200000 Trklfufi 9 budiwrd5mrfo5WirfulblrwuFmfulTrklfufi$KfukwiFmfulTrklfufiRvht@,)8e(:e8
07-24 12:39:10.455: E/fail!(19711): Error convert stream to String: java.lang.NullPointerException
07-24 12:39:10.455: E/fail!(19711): Error convert stream to String: java.lang.NullPointerException
07-24 12:39:10.455: E/JSON Parser(19711): Error parsing data org.json.JSONException: End of input at character 0 of
07-24 12:39:10.455: E/JSON Parser(19711): Error parsing data org.json.JSONException: End of input at character 0 of
07-24 12:39:10.455: D/AndroidRuntime(19711): Shutting down VM
07-24 12:39:10.455: W/dalvikvm(19711): threadid=1: thread exiting with uncaught exception (group=0x41e7f2a0)
07-24 12:39:10.460: E/AndroidRuntime(19711): FATAL EXCEPTION: main
07-24 12:39:10.460: E/AndroidRuntime(19711): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mykong.android/com.mykong.android.JSonResultActivity}: java.lang.NullPointerException
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread.access$700(ActivityThread.java:140)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.os.Handler.dispatchMessage(Handler.java:99)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.os.Looper.loop(Looper.java:137)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread.main(ActivityThread.java:4921)
07-24 12:39:10.460: E/AndroidRuntime(19711): at java.lang.reflect.Method.invokeNative(Native Method)
07-24 12:39:10.460: E/AndroidRuntime(19711): at java.lang.reflect.Method.invoke(Method.java:511)
07-24 12:39:10.460: E/AndroidRuntime(19711): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
07-24 12:39:10.460: E/AndroidRuntime(19711): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
07-24 12:39:10.460: E/AndroidRuntime(19711): at dalvik.system.NativeStart.main(Native Method)
07-24 12:39:10.460: E/AndroidRuntime(19711): Caused by: java.lang.NullPointerException
07-24 12:39:10.460: E/AndroidRuntime(19711): at com.mykong.android.JSonResultActivity.onCreate(JSonResultActivity.java:65)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.Activity.performCreate(Activity.java:5206)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
07-24 12:39:10.460: E/AndroidRuntime(19711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
07-24 12:39:10.460: E/AndroidRuntime(19711): ... 11 more
这是我的解析器
public class BackgroundTask extends AsyncTask<String, Void, JSONObject> {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// variables passed in:
String url;
String method;
List<NameValuePair> params;
// constructor
public BackgroundTask(String url, String method,
List<NameValuePair> params) {
this.url = url;
this.method = method;
this.params = params;
}
@Override
protected JSONObject doInBackground(String... args) {
try {
if(method == "POST"){
DefaultHttpClient httpClient = new DefaultHttpClient();
httpClient.getParams().setParameter(ClientPNames.COOKIE_POLICY,
CookiePolicy.BROWSER_COMPATIBILITY);
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} else if(method == "GET"){
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("fail!", "Error convert stream to String: " + e.toString());
}
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
return jObj;
}
@Override
protected void onPostExecute(JSONObject obj) {
}
}
这是显示列表的活动
public class JSonResultActivity extends ListActivity {
// déclarer l’URL du fichier employes.json
private static String url = "https://api.foursquare.com/v2/venues/search?ll=40.7,-74&radius=0&client_id=50QO00GZKUPA25PDGO1IY3UHMK3IBEMO2F4CTO5M2DBLVGQD&client_secret=MVJZGC3WT4V55DQPJYBFNZ5X3IACIDLFVM1HKA2WBTEHAXDF&v=20130703";
private static final String TAG_VENUES = "venues";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_LOCATION = "location";
private static final String TAG_ADDRESS = "adresse";
private static final String TAG_CROSS_STREET = "crossStreet";
private static final String TAG_CITY = "city";
private static final String TAG_STATE = "state";
private static final String TAG_POSTAL_CODE = "postalCode";
private static final String TAG_COUNTRY = "country";
private static final String TAG_LAT = "lat";
private static final String TAG_LNG = "lng";
private static final String TAG_DISTANCE = "distance";
// initialiser à null notre liste d’employés (de type JSONArray)
JSONArray venues = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// création de la ArrayList qui nous permettra de remplir la listView
ArrayList<HashMap<String, String>> venuesList = new ArrayList<HashMap<String, String>>();
// instancier la classe JsonParser
//JsonParser jParser = new JsonParser ();
BackgroundTask backgroundTask = new BackgroundTask(null, null, null);
backgroundTask.execute(url);
// récupérer le JSONObject à partir de l’url
//JSONObject json = jParser.getJSONFromUrl(url);
JSONObject json = backgroundTask.doInBackground(url);
try {
// récupérer la liste de tous les employés
venues = json.getJSONArray(TAG_VENUES);
// parcourir toute la liste des employés
for(int i = 0; i < venues.length(); i++){
// récupérer un employé de type JSONObject
JSONObject ven = venues.getJSONObject(i);
// stocker chaque item du JSONObject employe dans une variable de type String
String id = ven.getString(TAG_ID);
String name = ven.getString(TAG_NAME);
// récupérer le JSONObject phone qui contient deux items
JSONObject location = ven.getJSONObject(TAG_LOCATION);
String address = location.getString(TAG_ADDRESS);
String crossStreet= location.getString(TAG_CROSS_STREET);
String city= location.getString(TAG_CITY);
String state= location.getString(TAG_STATE);
String postalCode= location.getString(TAG_POSTAL_CODE);
String country= location.getString(TAG_COUNTRY);
String lat= location.getString(TAG_LAT);
String lng= location.getString(TAG_LNG);
String distance= location.getString(TAG_DISTANCE);
// créer une HashMap pour ajouter les informations dans chaque item
HashMap<String, String> map = new HashMap<String, String>();
// insérer dans la HashMap les données que l’on veut afficher sous la forme de clé/valeur
map.put(TAG_ID, id);
map.put(TAG_NAME, name);
map.put(TAG_CITY, city);
map.put(TAG_LAT, lat);
map.put(TAG_LNG, lng);
map.put(TAG_DISTANCE, distance);
// ajouter une HashMap à notre ArrayList
venuesList.add(map);
}
} catch (JSONException e)
{
e.printStackTrace();
}
//créer un SimpleAdapter qui se chargera de placer les données dans chaque item de notre listView
ListAdapter adapter = new SimpleAdapter(this, venuesList,R.layout.activity_json_result, new String[] { TAG_NAME, TAG_ADDRESS, TAG_LAT, TAG_LNG },
new int[] {R.id.name, R.id.address, R.id.lat, R.id.lng });
// attribuer à notre listView l'adapter que l'on vient de créer
setListAdapter(adapter);
}
}
我该如何解决这个问题？
谢谢您的帮助。