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我有一个在我的 asynctask 中运行的进度对话框，当 asynctask 需要一段时间才能加载时，我希望用户能够按 android 设备上的后退来阻止 asynctask 完成。我自己进行了研究，看看我是否可以自己做，但我对你可以使用的不同方法感到不知所措。我已经看过几个关于 stackoverflow 的问题，但每个人都有不同的方法并使用不同的方法。所以我只是希望有人能帮助我，告诉我我需要做什么来应对我的特殊情况。我也很乐意阅读教程。

public class ListView extends ListActivity {    


    ArrayList<HashMap<String, String>> questionList;        

     final String TAG_RESULTS = "results";
     final String TAG_QUESTION_SUBJECT = "Subject";
     final String TAG_QUESTION_NUMANSWERS = "NumAnswers";
     final String TAG_QUESTION = "question";
     final String TAG_QUESTION_CONTENT = "Content";
     final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer";
     final String TAG_ANSWERS = "Answers";
     final String TAG_ANSWER = "Answer";    
     final String TAG_ANSWERS_CONTENT = "content";      
     final String TAG_QUERY = "query";
     ProgressDialog pDialog;

            JSONArray question = null;          
            android.widget.ListView lv;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState); 
        //setContentView(R.layout.listview);        

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


    new LoadAllData().execute();

        }


    @Override   
    protected void onListItemClick(android.widget.ListView l, View v, int pos, long id) {
         super.onListItemClick(l, v, pos, id);  

          HashMap<String, String> item = questionList.get(pos);

          Intent i = new Intent(ListView.this, SingleListItem.class);
          i.putExtra(TAG_QUESTION_SUBJECT, item.get(TAG_QUESTION_SUBJECT));
          i.putExtra(TAG_QUESTION_CONTENT, item.get(TAG_QUESTION_CONTENT));
          i.putExtra(TAG_QUESTION_CHOSENANSWER, item.get(TAG_QUESTION_CHOSENANSWER));
          startActivity(i);

            }     

    class LoadAllData extends AsyncTask<String, String, String> {


        @Override
        protected void onPreExecute() {
            super.onPreExecute();             
            pDialog = new ProgressDialog(ListView.this);
            pDialog.setMessage("Loading Data. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        protected String doInBackground(String... args) {

            try {
                Intent in = getIntent();
                String searchTerm = in.getStringExtra("TAG_SEARCH");
                String query = URLEncoder.encode(searchTerm, "utf-8");
                String URL = "http://example.com";
                JSONParsser jParser = new JSONParsser();
                JSONObject json = jParser.readJSONFeed(URL);
                try {

                    JSONArray questions = json.getJSONObject("all").getJSONArray("questions");

                    for(int i = 0; i < questions.length(); i++) {
                        JSONObject question = questions.getJSONObject(i);


                    String Subject = question.getString(TAG_QUESTION_SUBJECT);
                    String ChosenAnswer = question.getString(TAG_QUESTION_CHOSENANSWER);
                    String Content = question.getString(TAG_QUESTION_CONTENT);

                    //JSONArray Answers = question.getJSONObject(TAG_ANSWERS).getJSONArray(TAG_ANSWER);


                    //JSONObject Answer = Answers.getJSONObject(0);

                    //String Content = Answer.getString(TAG_ANSWERS_CONTENT);

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

                               map.put(TAG_QUESTION_SUBJECT, Subject);
                               map.put(TAG_QUESTION_CONTENT, Content);
                               map.put(TAG_QUESTION_CHOSENANSWER, ChosenAnswer);

                               questionList.add(map);

                    }


                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            } catch (UnsupportedEncodingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

                return TAG_QUESTION ;           

        }

        @Override
        protected void onPostExecute(String file_URL) {
            if (pDialog != null && pDialog.isShowing()) pDialog.dismiss();
            ListAdapter adapter = new SimpleAdapter(getBaseContext(), questionList,
                        R.layout.listelements,
                        new String[] { TAG_QUESTION_SUBJECT }, new int[] {
                        R.id.Subject,});

                setListAdapter(adapter);                

        }       
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();
    }   
}
4

1 回答 1

0

像这样使用。

1) 对于取消异步任务

@Override
public void onBackPressed() 
{              
    /** If user Pressed BackButton While Running Asynctask
        this will close the ASynctask.
     */
    if (mTask != null && mTask.getStatus() != AsyncTask.Status.FINISHED)
    {
        mTask.cancel(true);
    }          
    super.onBackPressed();
}


@Override
protected void onDestroy() {
    // TODO Auto-generated method stub


/** If Activity is Destroyed While Running Asynctask
        this will close the ASynctask.   */

 if (mTask != null && mTask.getStatus() != AsyncTask.Status.FINISHED)
 {
    mTask.cancel(true);
  }  

    super.onDestroy();

}

2) 对于取消进度对话框

@Override
protected void onPause() {
    // TODO Auto-generated method stub


 if (mProgressDialog != null)
 {
     if(mProgressDialog.isShowing())
     {
         mProgressDialog.dismiss();
     }
        super.onPause();

  }  

}

编辑：以这种方式使用 Asynctask 将 Asynctask 声明为全局变量

 LoadAllData mTask;

& 初始化onCreate(..) 

mTask=new LoadAllData(YourActivity.this);

＆ 执行

mTask.execute("yourString");
于 2013-08-25T04:21:40.180 回答