NPE在填充的ListView使用JSON

public class DisplayServiceActivity extends ListActivity { 
private ListView listOfServices; 

//JSONArrays? 
JSONArray directory = null; 

//JSON Node names 
private static String TAG_ID = "id"; 
private static String TAG_NAME= "name"; 
private static String TAG_DIRECTORY = "Categories"; 
private final static String url; 
JSONObject json; 
jsonParser jParser = new jsonParser(); 

@SuppressLint("NewApi") 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    Request request = new Request(); 
    request.execute(); 

    listOfServices =getListView(); //get builtin listView 


    ArrayList<HashMap<String, String>> directoryList = new ArrayList<HashMap<String, String>>(); 

    try{ 
     //getting Array 
     directory = json.getJSONArray(TAG_DIRECTORY); 

     for(int i= 0; i<directory.length(); i++){ 
      JSONObject addItem =directory.getJSONObject(i); 

      //store each item in variable 
      String id = addItem.getString(TAG_ID); 
      String name= addItem.getString(TAG_NAME); 

      //create new HashMap 
      HashMap<String,String> map = new HashMap<String, String>(); 

      //add each child node to HashMap key 
      map.put(TAG_ID, id); 
      map.put(TAG_NAME, name); 

      //adding HashList to ArrarList 
      directoryList.add(map); 
     } 

    } catch (JSONException e){ 
     e.printStackTrace(); 
    } 

    ListAdapter adapter = new SimpleAdapter(this, 
      directoryList, 
      R.layout.list_item, 
      new String[] { TAG_ID,TAG_NAME }, 
      new int[] { android.R.id.text1,android.R.id.text2 }); 

    setListAdapter(adapter); 
    setContentView(R.layout.service); 
    // Make sure we're running on Honeycomb or higher to use ActionBar APIs 
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { 
     // Show the Up button in the action bar. 
     getActionBar().setDisplayHomeAsUpEnabled(true); 
    } 
}// end of onCreate Method 

public class Request extends AsyncTask<Void, Void, Void> { 
    protected Void doInBackground(Void... params) { 
     json = jParser.getJSONfromURL(url); 
     return null; 
    } 
    @Override 
    protected void onPostExecute(Void v) {   
     super.onPostExecute(v); 
    } 

} 


@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
    case android.R.id.home: 
     NavUtils.navigateUpFromSameTask(this); 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
}

}NPE在填充的ListView使用JSON

我試圖在從按鈕開始一個新的活動來填充使用JSON列表視圖。在調試時我收到一個NPE。這裏是日誌的貓，當我開始練習，然後點擊按鈕開始displayServicesActivity

---------- 
05-12 00:36:57.012: I/Adreno200-EGLSUB(18696): <ConfigWindowMatch:2081>: Format RGBA_8888. 

05-12 00:36:57.022: D/memalloc(18696): /dev/pmem: Mapped buffer base:0x50755000 size:3112960 offset:2498560 fd:54 

05-12 00:36:57.243: D/memalloc(18696): /dev/pmem: Mapped buffer base:0x50c44000 size:4956160 offset:4341760 fd:57 

05-12 00:37:05.511: D/memalloc(18696): /dev/pmem: Mapped buffer base:0x511fe000 size:2416640 offset:1802240 fd:60 

05-12 00:37:07.853: W/dalvikvm(18696): threadid=1: thread exiting with uncaught exception (group=0x40a601f8) 

05-12 00:37:07.863: E/AndroidRuntime(18696): FATAL EXCEPTION: main 

05-12 00:37:07.863: E/AndroidRuntime(18696): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.hstnc_activity/com.example.hstnc_activity.DisplayServiceActivity}: java.lang.NullPointerException 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.ActivityThread.access$600(ActivityThread.java:123) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.os.Handler.dispatchMessage(Handler.java:99) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.os.Looper.loop(Looper.java:137) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.ActivityThread.main(ActivityThread.java:4424) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at java.lang.reflect.Method.invokeNative(Native Method) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at java.lang.reflect.Method.invoke(Method.java:511) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:812) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:579) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at dalvik.system.NativeStart.main(Native Method) 

05-12 00:37:07.863: E/AndroidRuntime(18696): Caused by: java.lang.NullPointerException 

05-12 00:37:07.863: E/AndroidRuntime(18696): at com.example.hstnc_activity.DisplayServiceActivity.onCreate(DisplayServiceActivity.java:59) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.Activity.performCreate(Activity.java:4465) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 

05-12 00:37:07.863: E/AndroidRuntime(18696): at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 

05-12 00:37:07.863: E/AndroidRuntime(18696): ... 11 more 

05-12 00:37:08.193: E/JSON Parser Error(18696): Error parsing data org.json.JSONException: Value <!DOCTYPE of type java.lang.String cannot be converted to JSONObject

來源

2013-05-12 user2374128

什麼是在第59行運行？ – codeMagic 2013-05-12 05:01:44

你得到的是html的東西'<！類型的DOCTYPE，而不是JSON，因此你崩潰了''onCreate'。這個堆棧跟蹤中的最後一行是你的罪魁禍首。 – 2013-05-12 05:04:22

它看起來像你的JSONArray是沒有得到來自AsyncTask填充調用方法length()之前它，所以它正在返回null，因此您的NPE。

把這些代碼在你的onPostExecute()所以它不會運行，直到後doInBackground()已經完成，它會在UI Thread

來源

2013-05-12 05:15:14 codeMagic

NPE在填充的ListView使用JSON

回答

相關問題