我正在开发一个应用程序，它（在AsyncTask中）执行查询到远程服务器获取JSON字符串。 为了在我的ListView上显示数据，我扩展了一个ArrayAdapter。
当我执行我的应用程序时，从LogCat我可以看到数据被正确检索但未在ListView中显示。
我必须使一切正常（并且数据显示在ListView上）的唯一方法是在调试模式下运行应用程序，在行上设置断点
myListView 的 setAdapter （ myAdapter ）;
等待几秒钟然后恢复申请。 完成此过程后，一切正常。
为什么会这样？
AsyncTask是否适合进行如此长时间的操作，或者我应该使用其他方法（但我不知道哪一种方法！）。
这是MainActivity代码
public class MainActivityFragment extends Fragment {
private List<Station> stationList = new ArrayList<Station>();
private StationAdapter stationsAdapter;
private ProgressDialog pd;
private String LOG_TAG = "ProvaAsyncTask";
public MainActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
mioAsync mioTask = new mioAsync();
mioTask.execute();
stationsAdapter = new StationAdapter(stationList, getActivity());
ListView stationsListView = (ListView) rootView.findViewById(R.id.miaListView);
stationsListView.setAdapter(stationsAdapter);
return rootView;
}
public class mioAsync extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Creo la ProgressDialog che precede il caricamento dei dati
pd = new ProgressDialog(getActivity());
pd.setMessage(MainActivityFragment.this.getString(R.string.preloader_stations_list));
pd.show();
}
@Override
protected Void doInBackground(Void... params) {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String forecastJsonStr = null;
try {
URL url = new URL("*remoteserver*");
// Create the request to the server, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
return null;
} finally{
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
try{
getStationsListFromJson(forecastJsonStr);
} catch (JSONException e) {
Log.e(LOG_TAG, e.getMessage(), e);
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
pd.dismiss();
}
private void getStationsListFromJson(String stationsJsonStr) throws JSONException {
JSONArray stationsArray = new JSONArray(stationsJsonStr);
String nomeStaz;
String numSat;
stationList.clear();
for (int i = 0; i < stationsArray.length(); i++) {
JSONObject j = stationsArray.optJSONObject(i);
Iterator it = j.keys();
while (it.hasNext()) {
String n = it.next().toString();
numSat = j.getString(n) + " stazioni";
n = it.next().toString();
nomeStaz = j.getString(n);
stationList.add(new Station(nomeStaz, numSat));
}
}
}
}
}
我得到的JSON字符串就像这样
[{"nome":"Station1","satelliti":"11"},{"nome":"Station2","satelliti":"9"},{"nome":"Station3","satelliti":"8"}]
这是我扩展ArrayList
的地方public class StationAdapter extends ArrayAdapter<Station> {
private List<Station> stationsList;
private Context context;
public StationAdapter(List<Station> lista, Context cont){
super(cont, R.layout.listitems, lista);
this.stationsList = lista;
this.context = cont;
}
public int getCount() {
return stationsList.size();
}
public Station getItem(int position) {
return stationsList.get(position);
}
public long getItemId(int position) {
return stationsList.get(position).hashCode();
}
public View getView(int position, View convertView, ViewGroup parent){
View v = convertView;
StationHolder holder = new StationHolder();
// controllo che il convertview non sia null
if (convertView == null){
// This a new view we inflate the new layout
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = inflater.inflate(R.layout.listitems, null);
// Now we can fill the layout with the right values
TextView stationName = (TextView) v.findViewById(R.id.testataUno);
TextView satellitesNumber = (TextView) v.findViewById(R.id.testataDue);
holder.stationNameView = stationName;
holder.satellitesNumberView = satellitesNumber;
v.setTag(holder);
} else {
holder = (StationHolder) v.getTag();
}
Station p = stationsList.get(position);
holder.stationNameView.setText(p.getName());
holder.satellitesNumberView.setText("" + p.getSatellites());
return v;
}
/* *********************************
* We use the holder pattern
* It makes the view faster and avoid finding the component
* **********************************/
private static class StationHolder {
public TextView stationNameView;
public TextView satellitesNumberView;
}
}
这是电台代码
public class Station {
private String name;
private String satellites;
public Station(String nome, String satelliti){
this.name = nome;
this.satellites = satelliti;
}
public String getName(){
return this.name;
}
public String getSatellites(){
return this.satellites;
}
public void setName(String nome){
this.name = nome;
}
public void setSatellites(String satelliti){
this.satellites = satelliti;
}
}
答案 0 :(得分：2)
你的流量被打破了。它只能在调试模式下工作，因为你在断点上停止执行UI线程，但在你的断点之前排除了你的AsyncTask，并且由于没有停止，它会在你喜欢你的断点时下载数据。你很可能认为AsyncTask（它是异步任务的缩写）是......好......同步。不是。你的主要代码不会等待asynctask，它会启动并继续。您需要重新编写代码，并在asynctask的onPostExecute()方法中根据下载的内容更新数据集，然后在列表的适配器上调用notifyDatasetChanged()。这应该触发列表刷新。