從asyncTask通過監聽器返回HTTP-JSON數據到活動

Question

我試圖從我的AsyncTask擴展類中返回JSON數據到我的Activity。 我的活動代碼如下：

public class MainActivity extends Activity implements JSONListener{ 

     private JSONObject jsonData = null; 

     @Override 
     public void JSONFeedBack(JSONObject jsonData) { 
      // TODO Auto-generated method stub 
      this.jsonData = jsonData; 
      Log.e("JSON check in JSONFeedBack(): ", jsonData.toString() ); 
     } 

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

      new JsonObj(this).execute("http://xml/url"); 

     } 
    } 

我JSONListener如下：

import org.json.JSONObject; 

public interface JSONListener { 
    void JSONFeedBack(JSONObject jsonObj); 
} 

而我的AsyncTask類如下：通過HTTP

public class JsonObj extends AsyncTask<String, Void, JSONObject>{ 
    MainActivity activity; 
    JSONListener jsonListener; 
    int tid; 
    String term; 

    public JsonObj(JSONListener jsonListener){ 
     this.jsonListener = jsonListener; 
    } 

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

     // TODO Auto-generated method stub 
     DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams()); 
     HttpPost httppost = new HttpPost(url[0]); 
     JSONObject jsonObject = null; 
     // Depends on your web service 
     httppost.setHeader("Content-type", "application/json"); 

     InputStream inputStream = null; 
     String result = null; 
     try { 
      HttpResponse response = httpclient.execute(httppost);   
      HttpEntity entity = response.getEntity(); 

      inputStream = entity.getContent(); 
      // json is UTF-8 by default 
      BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8); 
      StringBuilder sb = new StringBuilder(); 

      String line = null; 
      while ((line = reader.readLine()) != null){ 
       sb.append(line + "\n"); 
      } 
      result = sb.toString(); 
      Log.e("JSON-Test [RESULT]: ", result); 
      jsonObject = new JSONObject(result); 


     } catch (Exception e) { 
      Log.e("JSON-Test [exception]: ", e.toString()); 
     } 
     finally { 
      try{if(inputStream != null)inputStream.close();}catch(Exception squish){} 
     } 

     return jsonObject; 
    } 

    @Override 
    protected void onPostExecute(JSONObject result) { 
     // TODO Auto-generated method stub 
     super.onPostExecute(result); 
     this.jsonListener.JSONFeedBack(result); 
     Log.e("OnPostExecute TEST: ", result.toString()); 

    } 
} 

實際JSON數據取 - 請求如下：

[ 
{ 
"data": { 
"term": "All Nations Praise", 
"tid": "10" 
} 
}, 
{ 
"data": { 
"term": "Classified Advertisements", 
"tid": "16" 
} 
}, 
{ 
"data": { 
"term": "Kid's", 
"tid": "11" 
} 
}, 
{ 
"data": { 
"term": "KT Creative", 
"tid": "9" 
} 
}, 
{ 
"data": { 
"term": "KT Diary", 
"tid": "8" 
} 
}, 
{ 
"data": { 
"term": "Live at the Coronet", 
"tid": "14" 
} 
}, 
{ 
"data": { 
"term": "Situations Vacant", 
"tid": "15" 
} 
}, 
{ 
"data": { 
"term": "X:Change", 
"tid": "13" 
} 
}, 
{ 
"data": { 
"term": "Youth", 
"tid": "12" 
} 
} 
] 

因此，我在我的Activity類的JSONFeedBack中調用Log.e("JSON check in JSONFeedBack(): ", jsonData.toString());時遇到空指針異常。

我已經確認JSON數據是在AsynchClass中獲取的，但是我嘗試將它發送到活動會導致空指針異常。

Answer 1

我剛跑了你的代碼更改URL與我的服務之一，並能正常工作......我認爲，當你創建JSONObject

jsonObject = new JSONObject(result); 

你確定你沒有登錄問題這條線：

Log.e("JSON-Test [exception]: ", e.toString()); 

也就是說，如果我用這個網址http://puppygifs.tumblr.com/api/read/json我得到一個異常創建JSONObject，然後你得到的NPE。

我很確定AsynchTask和Activity之間的通信有效，問題出在你的迴應或你如何解析它。

Answer 2

不要將新行字符添加到Json字符串中。

String line = null; 
    while ((line = reader.readLine()) != null){ 
    sb.append(line); // remove + "\n" here 
} 

編輯：你應該在你的Log.e("JSON-Test [exception]: ", e.toString());