Question

我正在使用Simpleadapter创建一个Lisview来显示一些数据，但是我收到了这个错误：

java.lang.NullPointerException, at com.example.example.FindPeopleFragment.ListDrwaer(FindPeopleFragment.java:214)

代码

// Async Task to access the web
 private class JsonReadTask extends AsyncTask<String, Void, String> {
  @Override
  protected String doInBackground(String... params) {
   HttpClient httpclient = new DefaultHttpClient();
   HttpPost httppost = new HttpPost(params[0]);
   try {
    HttpResponse response = httpclient.execute(httppost);
    jsonResult = inputStreamToString(
      response.getEntity().getContent()).toString();
   }

   catch (ClientProtocolException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
   return null;
  }

  private StringBuilder inputStreamToString(InputStream is) {
   String rLine = "";
   StringBuilder answer = new StringBuilder();
   BufferedReader rd = new BufferedReader(new InputStreamReader(is));

   try {
    while ((rLine = rd.readLine()) != null) {
     answer.append(rLine);
    }
   }

   catch (IOException e) {
    // e.printStackTrace();
    Toast.makeText(getActivity(),
      "Error..." + e.toString(), Toast.LENGTH_LONG).show();
   }
   return answer;
  }

  @Override
  protected void onPostExecute(String result) {
   ListDrwaer();
  }
 }// end async task

 public void accessWebService() {
  JsonReadTask task = new JsonReadTask();
  // passes values for the urls string array
  task.execute(new String[] { url });
 }

 // build hash set for list view
 public void ListDrwaer() {
  List<Map<String, String>> employeeList = new ArrayList<Map<String, String>>();

  try {
   JSONObject jsonResponse = new JSONObject(jsonResult);
   JSONArray jsonMainNode = jsonResponse.optJSONArray("Utente");

   for (int i = 0; i < jsonMainNode.length(); i++) {
    JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
    String name = jsonChildNode.optString("Nome");
    String number = jsonChildNode.optString("Cognome");
    String string = jsonChildNode.optString("Stringa");
    String data = jsonChildNode.optString("DataLogin");
    String outPut = name + "-" + number + "-" + string  + "-" + data  ;
    Toast.makeText(getActivity(),outPut ,
         Toast.LENGTH_SHORT).show();
    employeeList.add(createEmployee("Utente", outPut));
   }
  } catch (JSONException e) {
   Toast.makeText(getActivity(), "Error" + e.toString(),
     Toast.LENGTH_SHORT).show();
  }

  SimpleAdapter simpleAdapter = new SimpleAdapter(getActivity(), employeeList,android.R.layout.simple_list_item_1,
          new String[] { "employees" },
          new int[] { android.R.id.text1 });

  listView.setAdapter(simpleAdapter);

 }

 private HashMap<String, String> createEmployee(String name, String number) {
  HashMap<String, String> employeeNameNo = new HashMap<String, String>();
  employeeNameNo.put(name, number);
  return employeeNameNo;
 }

最后一行是214行。为什么我收到此错误？

这是logcat：

11-20 10:49:23.287: E/AndroidRuntime(24897): Process: com.example.richapp, PID: 24897
11-20 10:49:23.287: E/AndroidRuntime(24897): java.lang.NullPointerException
11-20 10:49:23.287: E/AndroidRuntime(24897):    at com.example.richapp.FindPeopleFragment.ListDrwaer(FindPeopleFragment.java:214)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at com.example.richapp.FindPeopleFragment$JsonReadTask.onPostExecute(FindPeopleFragment.java:176)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at com.example.richapp.FindPeopleFragment$JsonReadTask.onPostExecute(FindPeopleFragment.java:1)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.os.AsyncTask.finish(AsyncTask.java:632)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.os.Handler.dispatchMessage(Handler.java:102)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.os.Looper.loop(Looper.java:157)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at android.app.ActivityThread.main(ActivityThread.java:5356)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at java.lang.reflect.Method.invokeNative(Native Method)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at java.lang.reflect.Method.invoke(Method.java:515)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
11-20 10:49:23.287: E/AndroidRuntime(24897):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

你一定有错误，你没有正确定义ArrayAdapter，它只有六个构造函数中的两个变量：

    ArrayAdapter(Context context, int resource, int textViewResourceId, T[] objects)
Constructor
ArrayAdapter(Context context, int resource, int textViewResourceId, List<T> objects)
Constructor

在您的代码中，您必须更改分配给new String[] { "employees" }的构造函数的第三个变量，并将要在每个listview项中使用的TextView的ID放在其位置，以便R.id.yourtextview和之后，您可以指定您可以在第四个变量中为您提供数据。可以在您创建的CustomArrayAdapter类中分配其他数据

在片段中设置数据时使用simpleAdapter的Android NullPointerException

1 个答案: