Android AsynTask PostExecute

Question

我有AsyncTask.class在這裏我解析json並返回列表，並在postExecute我需要將此列表添加到我的適配器並通知改變，但LogCat給錯誤，我該如何解決這個問題？

我的適配器有公共狀態，爲什麼我不能添加到他的結果？

FATAL EXCEPTION: main 
java.lang.NullPointerException 
    at com.gazetaimage.LoadTask.onPostExecute(LoadTask.java:84) 
    at com.gazetaimage.LoadTask.onPostExecute(LoadTask.java:1) 
    at android.os.AsyncTask.finish(AsyncTask.java:631) 
    at android.os.AsyncTask.access$600(AsyncTask.java:177) 
    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:137) 
    at android.app.ActivityThread.main(ActivityThread.java:5191) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562) 
    at dalvik.system.NativeStart.main(Native Method) 

LoadTask.java

public class LoadTask extends AsyncTask<Void, Void, List<String>> { 

    MainActivity main = new MainActivity(); 

    private int page = 1; 

    public int addPage(int i){ 
     return page = i; 
    } 

    @Override 
    protected List<String> doInBackground(Void... params) { 

     InputStream ips = null; 
     JSONObject jsonObj = null; 
     String json = "";  
     try { 
      DefaultHttpClient httpClient = new DefaultHttpClient(); 
      HttpResponse response = httpClient.execute(new HttpPost("http://iapp.gazeta.uz/fotolenta?page="+page)); 
      ips = response.getEntity().getContent(); 
     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 

     try { 
      BufferedReader bufff = new BufferedReader(new InputStreamReader(ips, "UTF-8")); 
      StringBuilder sb = new StringBuilder(); 
      String line = null; 

      while ((line = bufff.readLine()) != null){ 
       sb.append(line + "\n");     
      } 
      ips.close(); 
      json = sb.toString(); 

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

     try { 
      jsonObj = new JSONObject(json); 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 

     if(jsonObj != null){ 

     JSONArray array = jsonObj.optJSONArray("img_list"); 
      for (int i = 0; i < array.length(); i++) { 
       main.thumbs.add(array.optJSONObject(i).optString("thumbnail")); 
      } 
     } 
     else{ 
      Log.d("Log", "Nullll"); 
     } 

     return main.thumbs; 
    } 

    @Override 
    protected void onPostExecute(List<String> result) { 
     if (result != null){ 
      main.adapter.add(result);// HERE I HAVE Error 84 
     } 

    } 
} 

Answer 1

您不能在任務中創建活動的一個實例，並期望它會運行相同的活動..

相反，您可以創建interface，將它傳遞給AsyncTask（在構造函數中），然後調用方法onPostExecute

例如：

你的接口：

public interface OnTaskCompleted{ 
    void onTaskCompleted(values); 
} 

你的活動：

public YourActivity implements OnTaskCompleted{ 
    //your Activity 
    YourTask task = new YourTask(this); // here is the initalization code for your asyncTask 
} 

和你的AsyncTask：

public YourTask extends AsyncTask<Object,Object,Object>{ //change Object to required type 
    private OnTaskCompleted listener; 

    public YourTask(OnTaskCompleted listener){ 
     this.listener=listener; 
    } 

    //required methods 

    protected void onPostExecute(Object o){ 
     //your stuff 
     listener.onTaskCompleted(values); 
    } 
} 

從https://stackoverflow.com/a/9963705/1434631

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