如何在固定的時間間隔後重新列表listview？

Question

我做了一個演示，在其中顯示來自webservice的數據。哪個工作正常。當我第一次啓動服務時，我能夠在listview上顯示數據。但是我需要一次又一次地訪問服務器並獲取新數據。以獲得新的數據。但我需要在列表視圖中顯示新數據，但是當我獲得新數據時，列表變爲空白或空白。爲什麼？

這是我的代碼。

protected void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.departure_dashboard); 
    Log.d("=========onCreate", "constructor"); 

    try { 
     Bundle bundle = getIntent().getExtras(); 
     String message = bundle.getString("Response"); 
     Log.d("=========onCreate", message); 
     listView=(ListView)findViewById(R.id.listView1); 
     data = new Gson().fromJson(message, deparaturedaseboarddto.class); 
     adapter = new CustomListAdapter(this, data.getData()); 

     listView.setAdapter(adapter); 
     timer =new Timer(); 
     timer.scheduleAtFixedRate(new alertTask(), 0, 4000); 
    } catch (Exception e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

} 

當定時器開始我用alerk task.and調用webservice的連連

public class alertTask extends TimerTask { 

     @Override 
     public void run() { 
      // TODO Auto-generated method stub 
      WebserviceMethod callDepartudeDashboard=new WebserviceMethod(); 
      callDepartudeDashboard.setObserver(Departuredashboardscreen.this); 
      callDepartudeDashboard.getwebService(ConstantVariable.dashboardWebServiceURL+"a/"+"departuredashboard"+"?crsCode=hnh"); 


     } 

    } 

這是一次又一次的給予迴應的方法...

@Override 
     public void getWebserviceResponse(String result) { 
      // TODO Auto-generated method stub 
      Log.d("timer", result); 
      data.getData().clear(); 


      deparaturedaseboarddto localData = new Gson().fromJson(result, deparaturedaseboarddto.class); 
      data=localData 
      adapter.notifySetDataChanged(); 

     } 

這裏我的自定義適配器爲列表視圖

public class CustomListAdapter extends BaseAdapter{ 
    ArrayList<deparaturedaseboarddto> deparaturedaseboarddto; 
    private Context context; 
    public CustomListAdapter(Context context, ArrayList<deparaturedaseboarddto> deparaturedaseboarddto){ 
     this.deparaturedaseboarddto=deparaturedaseboarddto; 
     this.context = context; 
    } 

    @Override 
    public int getCount() { 
     // TODO Auto-generated method stub 
     return deparaturedaseboarddto.size(); 
    } 

    @Override 
    public Object getItem(int position) { 
     // TODO Auto-generated method stub 
     return deparaturedaseboarddto.get(position); 
    } 

    @Override 
    public long getItemId(int position) { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     // TODO Auto-generated method stub 
     View v = convertView; 
      if (v == null) { 
       LayoutInflater mInflater = (LayoutInflater) context 
         .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
       v = mInflater.inflate(R.layout.row_listitem, null); 
      } 

      final TextView platFormName = (TextView) v 
        .findViewById(R.id.item_platform); 

      final TextView schDepart = (TextView) v 
        .findViewById(R.id.item_schDepart); 
      final TextView expDepart = (TextView) v 
        .findViewById(R.id.item_expectdepart); 
      final TextView arrival = (TextView) v 
        .findViewById(R.id.item_arrival); 
      final TextView exparrival = (TextView) v 
        .findViewById(R.id.item_expertarrival); 
      final TextView stationName = (TextView) v 
        .findViewById(R.id.item_stationName); 

      final String platformValue = deparaturedaseboarddto.get(position).getPlatformNo(); 
      final String schDepartValue= deparaturedaseboarddto.get(position).getSchDepart(); 
      final String schExpectValue= deparaturedaseboarddto.get(position).getExpDepart(); 
      final String arrivalValue= deparaturedaseboarddto.get(position).getDestSchArrival(); 
      final String exparrivalValue= deparaturedaseboarddto.get(position).getDestSchArrival(); 
      String stationNameValue= deparaturedaseboarddto.get(position).getDestinationStation().getStationName(); 

      platFormName.setText(platformValue); 

      schDepart.setText(schDepartValue); 
      expDepart.setText(schExpectValue); 
      arrival.setText(arrivalValue); 
      exparrival.setText(exparrivalValue); 
      stationName.setText(stationNameValue); 
      return v; 
    } 

    public void notifySetDataChanged() { 
     // TODO Auto-generated method stub 
     notifyDataSetChanged(); 
    } 

} 

Answer 1

這是因爲你的適配器仍抱着舊的參考，當你調用data.getData().clear();

要澄清一下，當你第一次創建您的適配器被清空的數據集，

adapter = new CustomListAdapter(this, data.getData()); 

你傳入一個ArrayList， data.getData（）到你的適配器，那就是你的適配器將從中讀取數據的ArrayList。

現在，當您收到新數據時，您將數據指向localData，但您的適配器不知道這一點。的

@Override 
public void getWebserviceResponse(String result) { 
    // TODO Auto-generated method stub 
    Log.d("timer", result); 
    data.getData().clear(); 
    deparaturedaseboarddto localData = new Gson().fromJson(result,deparaturedaseboarddto.class); 
    data=localData; 
    adapter.notifySetDataChanged(); 
} 

所以與其做data = localData;，你應該做的data.addAll(localData.getData());然後調用notifyDataSetChanged（）;

基本上你想使用一個單獨的ArrayList，只是不斷從它中刪除數據並向它添加新的數據。