我一直在使用ListView和ArrayAdapter。现在我在使用ArrayAdapter进行更改时陷入了困境。
我正在使用AsyncTack来更新UI元素,即ListView,最初在onCreate()方法中设置了ListView的适配器,但是我要在AsyncTask的onPostExecute()方法中更改数组适配器。 / p>
以下是代码
ListView mListView = (ListView)findViewById(R.id.dataListView);
vAdapter = new ArrayAdapter(getActivity(), R.layout.list_item_data,strings);
mLisstView.setAdapter(vAdapter);
的AsyncTask
public class getDataFromServer extends AsyncTask<String,Void,String[]>{
public getDataFromServer() {
super();
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String[] doInBackground(String... parm) {
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
if(parm.length == 0){
return null;
}
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String getJsonStr = null;
try {
final String FORECAST_BASE_URL="http://myUrlToServer?";
final String QUERY_PARAM ="query";
final String FORMAT_PARAM ="mode";
final String UNITS_PARAM ="units";
Uri baseUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARAM,parm[0])
.appendQueryParameter(FORMAT_PARAM, format)
.appendQueryParameter(UNITS_PARAM,units)
.build();
Log.v("build Url: ",baseUri.toString());
URL url = new URL(baseUri.toString());
// Create the request 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;
}
getJsonStr = buffer.toString();
} catch (IOException e) {
return null;
} finally{
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e("Found in trouble", "Error closing stream", e);
}
}
}
try {
return getWeatherDataFromJson(getJsonStr,numDays);
}catch(JSONException ex){
ex.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String[] strings) {
super.onPostExecute(strings);
for(String s : strings)
Log.v("@ onPostExecute",s);
vAdapter = new ArrayAdapter(getActivity(), R.layout.list_item_data,strings);
vAdapter.notifyDataSetChanged();
/*if(strings != null){
vAdapter.clear();
for(String dayForecast : strings){
vAdapter.add(dayForecast);
}
}*/
}
}
注意:onPostExecute()方法中的注释代码也是通过逻辑正确但生成异常为UnsupportedOperationException而vAdapter.clear()
答案 0 :(得分:1)
你可以这样做:
onPostExecute()应如下所示:
@Override
protected void onPostExecute(String[] strings) {
super.onPostExecute(strings);
for(String s : strings)
Log.v("@ onPostExecute",s);
vAdapter.clear();
vAdapter.addAll(strings);
vAdapter.notifyDataSetChanged();
}
就是这样。