android asynctask致命异常

Question

我是AsyncTask的新手，所以遇到了一些错误。我只是有人告诉我什么是错的，我需要做些什么来解决它。我每次尝试这段代码都会得到一个致命的异常：AsyncTask＃1，所以有人可以帮助我。

07-25 03:47:57.526: W/dalvikvm(799): threadid=11: thread exiting with uncaught exception (group=0x40a71930) 
    07-25 03:47:57.666: E/AndroidRuntime(799): FATAL EXCEPTION: AsyncTask #1 
    07-25 03:47:57.666: E/AndroidRuntime(799): java.lang.RuntimeException: An error occured while executing doInBackground() 
    07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$3.done(AsyncTask.java:299) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.setException(FutureTask.java:219) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.run(FutureTask.java:239) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.lang.Thread.run(Thread.java:856) 
    07-25 03:47:57.666: E/AndroidRuntime(799): Caused by: java.lang.NullPointerException 
    07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.JSONParsser.getJSONFromURI(JSONParsser.java:35) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.asynctask.doInBackground(MainActivity.java:60) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.asynctask.doInBackground(MainActivity.java:1) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$2.call(AsyncTask.java:287) 
    07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.run(FutureTask.java:234) 

主要活动

public class MainActivity extends Activity { 

    EditText et; 
    Button getanswer; 

    JSONArray ResultsSet = null; {} 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 


     Button getanswer = (Button) findViewById(R.id.button1); 
     getanswer.setOnClickListener(new OnClickListener() { 


     @Override 
     public void onClick(View v) { 
      new asynctask().execute(); 

     } 

     }); 
    } 
} 

     class asynctask extends AsyncTask<String, Void, JSONObject> { 

      private static final String TAG_RESULTS = "ResultsSet"; 
      private static final String TAG_SUBJECT = "Subject"; 
      private static final String TAG_NUMANSWERS = "NumAnswers"; 
      private static final String TAG_QUESTION = "Question"; 
      private static final String TAG_QUESTION_CONTENT = "Content"; 
      private static final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer"; 
      private static final String TAG_QUESTION_ANSWERS = "Answers"; 
      public JSONArray json; 

     @Override 
     protected JSONObject doInBackground(String... params) { 

      JSONParsser jParser = new JSONParsser(); 

      String uRI = null; 

      JSONObject json = jParser.getJSONFromURI(uRI); 

      return json ; 

     }{ } 
      @Override 
      protected void onPostExecute(JSONObject json) { 

       JSONArray ResultsSet = null; { 
       try { 
        ResultsSet = json.getJSONArray(TAG_RESULTS); 
       } catch (JSONException e) { 
        e.printStackTrace(); 
      } 

      return; 

     }}} 

JSONParser类

public class JSONParsser { 

    static InputStream is = null; 
    static JSONObject jObj = null; 
    static String json = ""; 
    EditText et; 

    public JSONParsser() { 
    } 

    public JSONObject getJSONFromURI(String uRI) { 

     try{ 
     HttpClient client = new DefaultHttpClient(); 
     try { 
      URI website = new URI("http://answers.yahooapis.com/AnswerService/V1/questionSearch?appid=vcE15nV34EYK7oAge17Ws6nF3DOzc5ccb4PsWtQjW2YTG3gjKbz8exOHYQr6Psizg&query=" + et.getText() + "sort&type=resolved&results&output=json"); 
      HttpGet request = new HttpGet(); 
      request.setURI(website); 
      try { 
       HttpResponse response = client.execute(request); 
      HttpEntity httpEntity = response.getEntity(); 
      is = httpEntity.getContent(); 

      } catch (ClientProtocolException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } catch (IOException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
     } catch (URISyntaxException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
     return jObj; 

     }finally{} 

    }{ 

    }} 

InstanceofJSONParser类

public class JSONParserInstance { 

    JSONParsser jParser = new JSONParsser(); 

    public String uRI; 

    JSONObject json = jParser.getJSONFromURI(uRI); 


    private static final String TAG_RESULTS = "ResultsSet"; 
    private static final String TAG_SUBJECT = "Subject"; 
    private static final String TAG_NUMANSWERS = "NumAnswers"; 
    private static final String TAG_QUESTION = "Question"; 
    private static final String TAG_QUESTION_CONTENT = "Content"; 
    private static final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer"; 
    private static final String TAG_QUESTION_ANSWERS = "Answers"; 

      JSONArray ResultsSet = null; { 

    try { 
     ResultsSet = json.getJSONArray(TAG_RESULTS); 

     for(int i = 0; i < ResultsSet.length(); i++){ 
      JSONObject r = ResultsSet.getJSONObject(i); 

      String Subject = r.getString(TAG_SUBJECT); 
      String NmAnswers = r.getString(TAG_NUMANSWERS); 

      JSONObject Question = r.getJSONObject(TAG_QUESTION); 
      String Content = Question.getString(TAG_QUESTION_CONTENT); 
      String ChosenAnswer = Question.getString(TAG_QUESTION_CHOSENANSWER); 
      String Answers = Question.getString(TAG_QUESTION_ANSWERS); 

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

}}} 

Answer 1

在你的代码是null值传递给getJSONFromURI()，这是导致空指针异常

String uRI = null; 

JSONObject json = jParser.getJSONFromURI(uRI); // Passing null 

Answer 2

String uRI = null; 

JSONObject json = jParser.getJSONFromURI(uRI); 

您正试图解析空字符串，你越来越显示java.lang.NullPointerException

尝试new asynctask().execute(someUrl);代替new asynctask().execute();和改变String uRI = null;到String uRI = params[0]您doInBackground方法。

Answer 3

变化

@Override 
    protected JSONObject doInBackground(String... params) { 

     JSONParsser jParser = new JSONParsser(); 

     String uRI = null; 

     JSONObject json = jParser.getJSONFromURI(uRI); 

     return json ; 

    }{ } 

到

String uRI = null;//don't make it null 
@Override 
     protected JSONObject doInBackground(String... params) { 

      JSONParsser jParser = new JSONParsser(); 



      JSONObject json = jParser.getJSONFromURI(uRI); 

      return json ; 

     }