我尝试了下面的代码，并尝试了AsyncTaskLoader方法。当我实例化AsyncTask时，应用程序崩溃了。请告诉我关于在标签主机内的列表片段中加载JSON的最佳方法。
下面的代码是标签片段（我在主要活动中使用操作栏标签）：
public class TabTop extends ListFragment {
Context context = getActivity().getBaseContext();
String API_URL = "http://api.rottentomatoes.com/api/public/v1.0/movies/770672122/similar.json?apikey=crhhxb4accwwa6cy6fxrm8vj&limit=1";
ArrayList<Deal> deals;
DealsListAdapter adapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
@SuppressWarnings("unused")
int a = 0;
return super.onCreateView(inflater, container, savedInstanceState);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
GetTopDeals getTopDeals = new GetTopDeals(context);
getTopDeals.execute(API_URL);
super.onActivityCreated(savedInstanceState);
}
class GetTopDeals extends AsyncTask<String, Void, ArrayList<Deal>>{
ProgressDialog progressDialog;
public GetTopDeals(Context activity) {
this.progressDialog = new ProgressDialog(activity);
}
@Override
protected void onPostExecute(ArrayList<Deal> result) {
adapter = new DealsListAdapter(context, result);
setListAdapter(adapter);
super.onPostExecute(result);
}
@Override
protected void onPreExecute() {
progressDialog.setCancelable(true);
progressDialog.setProgress(0);
progressDialog.setMessage("loading Top deals...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
super.onPreExecute();
}
@Override
protected ArrayList<Deal> doInBackground(String... urls) {
String response = sendRequest(urls[0]); // make request for json
return processResponse(response); // parse the Json and return ArrayList to postExecute
}
private String sendRequest(String apiUrl) {
BufferedReader input = null; // get the json
HttpURLConnection httpCon = null; // the http connection object
StringBuilder response = new StringBuilder(); // hold all the data from the jason in string separated with "\n"
try {
URL url = new URL(apiUrl);
httpCon = (HttpURLConnection) url.openConnection();
if (httpCon.getResponseCode() != HttpURLConnection.HTTP_OK) { // check for connectivity with server
return null;
}
input = new BufferedReader(new InputStreamReader(httpCon.getInputStream())); // pull all the json from the site
String line;
while ((line = input.readLine()) != null) {
response.append(line + "\n");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (httpCon != null) {
httpCon.disconnect();
}
}
return response.toString();
}
}
public ArrayList<Deal> processResponse(String response) {
try {
JSONObject responseObject = new JSONObject(response); // Creates a new JSONObject with name/value mappings from the JSON string.
JSONArray results = responseObject.getJSONArray("movies"); // Returns the value mapped by name if it exists and is a JSONArray.
deals = new ArrayList<Deal>();
for (int i = 0; i < results.length(); i++) { // in this loop i copy the json array to movies arraylist in order to display listView
JSONObject jMovie = results.getJSONObject(i);
int api_id = jMovie.getInt("id");
String name = jMovie.getString("title");
String content = jMovie.getString("synopsis");
JSONObject posters = jMovie.getJSONObject("posters");
String image_url = posters.getString("profile");
}
}catch (JSONException e) {
e.printStackTrace();
}
return deals;
}
@Override
public void onStart() {
super.onStart();
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
Intent intent = new Intent(getActivity().getBaseContext(), DealInformation.class);
startActivity(intent);
super.onListItemClick(l, v, position, id);
}
}
答案 0 :(得分：1)
在他自己的档案中制作你的asynctask。
当你的asynctask完成后，实现自动调用的OnPostExecute。通过notifyDataSetChanged通知您的适配器：
@Override
protected void onPostExecute(List<NewItem> list) {
Adapter.getListe().clear();
Adapter.getListe().addAll(list);
Adapter.notifyDataSetChanged();
}
答案 1 :(得分：1)
我想发布我的回答。经过一些研究后，我决定选择AsyncTaskLoader。 这是我的代码
public class TabOurPicks extends ListFragment implements LoaderCallbacks<String[]> {
// when activity loads- onActivityCreated() calls the initLoader() who activate onCreateLoader()
@Override
public void onActivityCreated(Bundle savedInstance) {
super.onActivityCreated(savedInstance);
setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, new String[]{}));
getLoaderManager().initLoader(0, null,this).forceLoad();
}
// onCreateLoader instantiate the asynctaskloaser who work in bg
@Override
public RSSLoader onCreateLoader(int arg0, Bundle arg1) {
return new RSSLoader(getActivity()); //
}
// after bg process invoke onLoadFinished() who work in ui thread
@Override
public void onLoadFinished(Loader<String[]> loader, String[] data) {
setListAdapter(new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, data
) );
}
@Override
public void onLoaderReset(Loader<String[]> arg0) {
// TODO Auto-generated method stub
}
这是加载器的内部类：
static public class RSSLoader extends AsyncTaskLoader<String[]>
{
public RSSLoader(Context context) {
super(context);
}
@Override
public String[] loadInBackground() {
String url = "http://api.rottentomatoes.com/api/public/v1.0/movies/770672122/similar.json?apikey=crhhxb4accwwa6cy6fxrm8vj&limit=1";
String response = sendRequest(url);
return processResponse(response);
}
private String sendRequest(String url) {
BufferedReader input = null; // get the json
HttpURLConnection httpCon = null; // the http connection object
StringBuilder response = new StringBuilder(); // hold all the data from the jason in string separated with "\n"
try {
URL apiUrl = new URL(url);
httpCon = (HttpURLConnection) apiUrl.openConnection();
if (httpCon.getResponseCode() != HttpURLConnection.HTTP_OK) { // check for connectivity with server
return null;
}
input = new BufferedReader(new InputStreamReader(httpCon.getInputStream())); // pull all the json from the site
String line;
while ((line = input.readLine()) != null) {
response.append(line + "\n");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (httpCon != null) {
httpCon.disconnect();
}
}
return response.toString();
}
private String[] processResponse(String response) {
String[] deals = null;
try {
JSONObject responseObject = new JSONObject(response); // Creates a new JSONObject with name/value mappings from the JSON string.
JSONArray results = responseObject.getJSONArray("movies"); // Returns the value mapped by name if it exists and is a JSONArray.
deals = new String[10];
for (int i = 0; i < 9; i++) { // in this loop i copy the json array to movies arraylist in order to display listView
JSONObject jMovie = results.getJSONObject(i);
String name = jMovie.getString("title");
deals[i] = name;
}
}catch (JSONException e) {
e.printStackTrace();
}
return deals;
}
}
}
答案 2 :(得分：0)
asynctask是否有自己的文件并不重要。你只是不希望你的活动扩展asynctask，因为这会使你的活动异步 - 但由于java的双继承规则，这是不可能的。
根据应用程序的体系结构和编程风格，asyntask可以是活动中的内部类。在PostExecute方法上，确保已向适配器提供数据并将适配器设置为列表，然后运行notifyDataSetChanged（）。
假设您的asynctask正在从缓存或网络加载数据，那么您的方法就是正确的。