android中的异步任务有时会停止工作

Question

嘿，我制作了一个应用程序，其中有三个asynchronus类正在运行...它工作了一段时间，有时候其中一个类没有返回值......

这是我的代码......

public class DetailsTenderActivity extends Activity {

    final String url_bidnemo="http://www.myserver.com/index.php";
    public static DefaultHttpClient client;
    private static final String DEFAULT = "N/A";
    String tender_id="";
    String user_id="";
    TextView basic_dets;
    TextView other_dets;
    TextView item_dets;
    public final static String EXTRA_MESSAGE6 = "com.mobile.bidnemo.MESSAGE6";
    public final static String EXTRA_MESSAGE7 = "com.mobile.bidnemo.MESSAGE7";
    public final static String EXTRA_MESSAGE8 = "com.mobile.bidnemo.MESSAGE8";
    public final static String EXTRA_MESSAGE9 = "com.mobile.bidnemo.MESSAGE9";

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

        setTitle("Tender details");

        Downloadbasic dw_basic=new Downloadbasic();
        dw_basic.execute();

        Downloadother dw_other=new Downloadother();
        dw_other.execute();

        Downloaditems dw_items=new Downloaditems();
        dw_items.execute();



        final ProgressDialog pd=new ProgressDialog(this);
        pd.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        pd.setMessage("Please wait..");
        pd.setIndeterminate(true);
        pd.setCancelable(true);

        /**check session exist or not start****************************/
        SharedPreferences share= getSharedPreferences("Userdata", Context.MODE_PRIVATE);
        String val=share.getString("session_value", DEFAULT);
        if(DEFAULT.equals(val)){
        Intent intent=new Intent(DetailsTenderActivity.this,Main.class);
        startActivity(intent);
        }
        else{
        Intent intent = getIntent();
        tender_id = intent.getStringExtra(TenderViewActivity.EXTRA_MESSAGE2);
        user_id=val;



      //  basic_dets.setText(details_info("basic"));    
      //  other_dets.setText(details_info("other"));    
      //  item_dets.setText(item_info());

        Button bid_button=(Button) findViewById(R.id.button1);
        bid_button.setText(bid_activity_info());
        }
        /**check session exist or not end*****************************/


        /**Place bid process start*******/
        Button place_bid=(Button) findViewById(R.id.button1);
        place_bid.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
        pd.show();
        Intent intent=new Intent(DetailsTenderActivity.this,PlaceBidActivity.class);
        intent.putExtra(EXTRA_MESSAGE6, tender_id);
        intent.putExtra(EXTRA_MESSAGE7, user_id);
        intent.putExtra(EXTRA_MESSAGE8, bid_activity_info());
        intent.putExtra(EXTRA_MESSAGE9, partial_check());
        startActivity(intent);
        }
        });
        /**Place bid process end*********/

        placebid_button_prop();

        }//onCreate



    @SuppressWarnings("unused")
    private class Downloadbasic extends AsyncTask<String, String, String> {

        @Override
        protected String doInBackground(String... params) {
        String getval=details_info("basic");
        return getval;  
        }

        protected void onPostExecute(String result) {
        super.onPostExecute(result);
        TextView basic_dets=(TextView) findViewById(R.id.basic_details);
        basic_dets.setText(result);
         }

     }


    @SuppressWarnings("unused")
    private class Downloadother extends AsyncTask<String, String, String> {

        @Override
        protected String doInBackground(String... params) {
        String getval=details_info("other");
        return getval;  
        }

        protected void onPostExecute(String result) {
        TextView other_dets=(TextView) findViewById(R.id.other_details);
        other_dets.setText(result);
         }

     }



    @SuppressWarnings("unused")
    private class Downloaditems extends AsyncTask<String, String, String> {

        @Override
        protected String doInBackground(String... params) {
        String getval=item_info();
        return getval;  
        }

        protected void onPostExecute(String result) {
        TextView item_dets=(TextView) findViewById(R.id.item_details);
        item_dets.setText(result);
         }

     }

上面的代码工作正常，但大多数时候一两个asynchrouns类没有返回结果它仍然是空白的...不知道为什么......