java - 如何在固定时间间隔后刷新listview？

Question

我制作了演示，其中显示来自网络服务的数据。它工作正常。这意味着当我第一次访问服务时，我能够在 ListView 上显示数据。但是我需要一次又一次地访问服务器并获取新数据。我是能够获取新数据。但我需要在 ListView 上显示新数据，但当我获取新数据时，我的列表变为空白或为空。为什么？

这是我的代码。

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();
    }

}

当计时器启动时，我使用了alerk任务，并一次又一次调用web服务

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");


        }

    }

这是一次又一次给出响应的方法...

@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();

        }

这是我的 ListView 自定义适配器

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

这是因为您的适配器仍然保留对数据集的旧引用，当您调用 data.getData().clear();

时该数据集被清空

澄清一下，当您第一次创建适配器时，

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

您正在将 ArrayList data.getData() 传递给您的适配器，这就是您的适配器将从中读取数据的 ArrayList。

现在，当您收到新数据时，您将数据指向 localData，但您的适配器不知道这一点。

@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();
}

因此，您不应执行 data = localData;，而应该执行 data.addAll(localData.getData());，然后调用 notificationDataSetChanged();

基本上，您想使用一个 ArrayList，然后不断地从中删除数据并向其中添加新数据。