当我调用 asynctask 函数时，数据被加载并显示在列表视图中，但是每当我进入这个活动时，每次该函数执行并再次加载数据。但我只希望该函数调用一次并显示在列表视图中。那么解决方案是什么。
这是我的完整课程代码：
public class Feed extends Fragment implements
PullToRefreshAttacher.OnRefreshListener {
Button btnSlider;
ListView lv;
String userid, success, message, eventType, feed_title, feed_desc,
timeDate, like, commemt, Feeduserid, photo, posted, hasLike,
latsId, noMore, feed_id, category_id, feedImg, result;
InputStream is;
ProgressDialog pDialog;
InterNetConnectionDetector isNet = new InterNetConnectionDetector(
getActivity());
ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();
FeedAdapter fdp;
HashMap<String, String> map;
private uk.co.senab.actionbarpulltorefresh.library.PullToRefreshAttacher mPullToRefreshAttacher;
int limit = 5;
View v;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
v = inflater.inflate(R.layout.feed, container, false);
if (android.os.Build.VERSION.SDK_INT > 8) {
StrictMode.ThreadPolicy stp = new StrictMode.ThreadPolicy.Builder()
.permitAll().build();
StrictMode.setThreadPolicy(stp);
}
SharedPreferences pref = getActivity().getSharedPreferences("Login",
Activity.MODE_PRIVATE);
userid = pref.getString("user_id", "user_id");
btnSlider = (Button) v.findViewById(R.id.btnSlide);
lv = (ListView) v.findViewById(R.id.feed_ListView);
btnSlider.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
try {
Sliding.viewActionsContentView.showActions();
} catch (Exception e) {
// TODO: handle exception
}
}
});
try {
if (fdp == null) {
new FeedData().execute();
} else {
lv.setAdapter(fdp);
}
} catch (Exception e) {
// TODO: handle exception
}
mPullToRefreshAttacher = new uk.co.senab.actionbarpulltorefresh.library.PullToRefreshAttacher(
getActivity(), lv);
// Set Listener to know when a refresh should be started
mPullToRefreshAttacher
.setRefreshListener((uk.co.senab.actionbarpulltorefresh.library.PullToRefreshAttacher.OnRefreshListener) this);
((LoadMore) lv)
.setOnLoadMoreListener(new com.example.getconnected.LoadImage.LoadMore.OnLoadMoreListener() {
public void onLoadMore() {
// Do the work to load more items at the end of list
// here
new LoadDataTask().execute();
}
});
return v;
}
/*
* @Override protected void onCreate(Bundle savedInstanceState) { // TODO
* Auto-generated method stub super.onCreate(savedInstanceState);
* setContentView(R.layout.feed);
*
* if (Build.VERSION.SDK_INT >= 8) { getActionBar().hide(); }
*
* if (android.os.Build.VERSION.SDK_INT > 8) {
*
* StrictMode.ThreadPolicy stp = new StrictMode.ThreadPolicy.Builder()
* .permitAll().build(); StrictMode.setThreadPolicy(stp);
*
* }
*
* try { new FeedData().execute();
*
* } catch (Exception e) { // TODO: handle exception }
*
* SharedPreferences pref = getSharedPreferences("Login",
* Activity.MODE_PRIVATE); userid = pref.getString("user_id", "user_id");
*
* btnSlider = (Button) findViewById(R.id.btnSlide); lv = (ListView)
* findViewById(R.id.feed_ListView); btnSlider.setOnClickListener(new
* OnClickListener() {
*
* @Override public void onClick(View arg0) { // TODO Auto-generated method
* stub
*
* int width = (int) TypedValue.applyDimension( TypedValue.COMPLEX_UNIT_DIP,
* 40, getResources() .getDisplayMetrics());
* SlideoutActivity.prepare(getActivity(), R.id.inner_content, width);
* startActivity(new Intent(getActivity(), MenuActivity.class));
* getoverridePendingTransition(0, 0);
*
* } });
*
* mPullToRefreshAttacher = new PullToRefreshAttacher(getActivity(), lv);
*
* // Set Listener to know when a refresh should be started
* mPullToRefreshAttacher .setRefreshListener((OnRefreshListener)
* getActivity());
*
* ((LoadMore) lv) .setOnLoadMoreListener(new
* com.example.getconnected.LoadImage.LoadMore.OnLoadMoreListener() { public
* void onLoadMore() { // Do the work to load more items at the end of list
* // here new LoadDataTask().execute(); } }); }
*/
public class FeedData extends AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
pDialog = ProgressDialog.show(getActivity(), "", "Loading..");
pDialog.setCancelable(true);
}
@Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
return null;
}
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
// data=jobj.toString();
try {
DefaultHttpClient httpclient = new DefaultHttpClient();
String url = "http://www.sevenstarinfotech.com/projects/demo/GetConnected/api/feed.php?user_id="
+ userid + "&" + "limit=" + limit;
HttpPost httppost = new HttpPost(url);
Log.v("Feed Url:", url);
httppost.addHeader("Content-Type",
"application/x-www-form-urlencoded");
httppost.addHeader("app-key",
"b51bc98b4d6fd0456f7f1b17278415fa49de57d5");
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
try {
BufferedReader reader = new BufferedReader(
new InputStreamReader(is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
Log.v("Response is:", result);
} catch (Exception e3) {
Log.e("log_tag", "Error converting result " + e3.toString());
}
// parse json data
try {
JSONObject ja = new JSONObject(result);
JSONObject jdata = ja.getJSONObject("data");
success = jdata.getString("Success");
message = jdata.getString("Message");
latsId = jdata.getString("lastId");
noMore = jdata.getString("nomore");
JSONArray jArray = jdata.getJSONArray("Feeddetails");
for (int i = 0; i < jArray.length(); i++) {
map = new HashMap<String, String>();
JSONObject me = jArray.getJSONObject(i);
map.put("sucess", success);
map.put("message", message);
map.put("latsId", latsId);
map.put("noMore", noMore);
eventType = me.getString("type");
feed_id = me.getString("feed_id");
feed_title = me.getString("feed_title");
category_id = me.getString("category_id");
feed_desc = me.getString("feed_desc");
timeDate = me.getString("timeposted");
posted = me.getString("postedby");
like = me.getString("likes");
photo = me.getString("photo");
commemt = me.getString("comments");
Feeduserid = me.getString("user_id");
hasLike = me.getString("hasliked");
map.put("eventType", eventType);
map.put("feed_id", feed_id);
map.put("feed_title", feed_title);
map.put("category_id", category_id);
map.put("feed_desc", feed_desc);
map.put("timeDate", timeDate);
map.put("posted", posted);
map.put("like", like);
map.put("photo", photo);
map.put("commemt", commemt);
map.put("Feeduserid", Feeduserid);
map.put("hasLike", hasLike);
Log.v("Data:", feed_id + "/" + "/" + "/" + Feeduserid
+ "/" + "/" + "/" + like + "/" + "/" + "/"
+ commemt);
contactList.add(map);
}
Log.v("Length", contactList.size() + "");
} catch (Exception e1) {
Log.e("log_tag",
"Error in http connection " + e1.toString());
}
} catch (Exception e) {
// TODO: handle exception
}
pDialog.dismiss();
fdp = new FeedAdapter(getActivity(), contactList);
lv.setAdapter(fdp);
}
}
@Override
public void onRefreshStarted(View view) {
/**
* Simulate Refresh with 4 seconds sleep
*/
new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
try {
Thread.sleep(4000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Notify PullToRefreshAttacher that the refresh has finished
mPullToRefreshAttacher.setRefreshComplete();
}
}.execute();
}
private class LoadDataTask extends AsyncTask<String, Integer, String> {
@Override
protected String doInBackground(String... params) {
if (isCancelled()) {
return null;
}
// Simulates a background task
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
}
return null;
}
@Override
protected void onPostExecute(String result) {
try {
limit += 5;
DefaultHttpClient httpclient = new DefaultHttpClient();
String url = "http://www.sevenstarinfotech.com/projects/demo/GetConnected/api/feed.php?user_id="
+ userid + "&" + "limit=" + limit;
HttpPost httppost = new HttpPost(url);
Log.v("Feed Url:", url);
httppost.addHeader("Content-Type",
"application/x-www-form-urlencoded");
httppost.addHeader("app-key",
"b51bc98b4d6fd0456f7f1b17278415fa49de57d5");
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
try {
BufferedReader reader = new BufferedReader(
new InputStreamReader(is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
Log.v("Response is:", result);
} catch (Exception e3) {
Log.e("log_tag", "Error converting result " + e3.toString());
}
// parse json data
try {
JSONObject ja = new JSONObject(result);
JSONObject jdata = ja.getJSONObject("data");
success = jdata.getString("Success");
message = jdata.getString("Message");
latsId = jdata.getString("lastId");
noMore = jdata.getString("nomore");
JSONArray jArray = jdata.getJSONArray("Feeddetails");
for (int i = 0; i < jArray.length(); i++) {
map = new HashMap<String, String>();
JSONObject me = jArray.getJSONObject(i);
map.put("sucess", success);
map.put("message", message);
map.put("latsId", latsId);
map.put("noMore", noMore);
eventType = me.getString("type");
feed_id = me.getString("feed_id");
feed_title = me.getString("feed_title");
category_id = me.getString("category_id");
feed_desc = me.getString("feed_desc");
timeDate = me.getString("timeposted");
posted = me.getString("postedby");
like = me.getString("likes");
photo = me.getString("photo");
commemt = me.getString("comments");
Feeduserid = me.getString("user_id");
hasLike = me.getString("hasliked");
map.put("eventType", eventType);
map.put("feed_id", feed_id);
map.put("feed_title", feed_title);
map.put("category_id", category_id);
map.put("feed_desc", feed_desc);
map.put("timeDate", timeDate);
map.put("posted", posted);
map.put("like", like);
map.put("photo", photo);
map.put("commemt", commemt);
map.put("Feeduserid", Feeduserid);
map.put("hasLike", hasLike);
Log.v("Data:", feed_id + "/" + "/" + "/" + Feeduserid
+ "/" + "/" + "/" + like + "/" + "/" + "/"
+ commemt);
contactList.add(map);
}
pDialog.dismiss();
fdp = new FeedAdapter(getActivity(), contactList);
lv.setAdapter(fdp);
} catch (Exception e1) {
Log.e("log_tag",
"Error in http connection " + e1.toString());
}
} catch (Exception e) {
// TODO: handle exception
}
// mListItems.add("Added after load more");
// We need notify the adapter that the data have been changed
fdp.notifyDataSetChanged();
// Call onLoadMoreComplete when the LoadMore task, has finished
((LoadMore) lv).onLoadMoreComplete();
super.onPostExecute(result);
}
@Override
protected void onCancelled() {
// Notify the loading more operation has finished
((LoadMore) lv).onLoadMoreComplete();
}
}
}