android - Call AsyncTask in a Fragment -

i have class extends fragment. call asynctask class in fragment. doesn't obtain error in mylogcat doesn't display null in listview. below paste code use, code more simple, read json file , insert in custom listview. code works if change class in activity, want transform activity in fragment.

thanks in advance.

    public class myfragment extends fragment {  jsonparser jsonparser = new jsonparser(); arraylist<hashmap<string, string>> unilist; jsonarray articles = null;  listview list; listuniadapter adapter;  @override public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     new loadnews().execute(); }  @override public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate) {     linearlayout ll = (linearlayout)inflater.inflate(r.layout.uni_list, container, false);     list = (listview) ll.findviewbyid(android.r.id.list);     return ll; }  class loadnews extends asynctask<string, string, string> {     @override     protected void onpreexecute() {         super.onpreexecute();     }      protected string doinbackground(string... args) {         list<namevaluepair> params = new arraylist<namevaluepair>();         params.add(new basicnamevaluepair("s", "s"));          string json = jsonparser.makehttprequest(variable.url_universitometro, "get",                 params);          try {             unilist = new arraylist<hashmap<string, string>>();             articles = new jsonarray(json);              if (articles != null) {                 (int = 0; < articles.length(); i++) {                     jsonobject c = articles.getjsonobject(i);                      string title = c.getstring(variable.uni_name);                     string voto = c.getstring(variable.uni_voto);                      hashmap<string, string> map = new hashmap<string, string>();                      map.put(variable.uni_name, title);                     map.put(variable.uni_voto, voto);                      unilist.add(map);                      if (iscancelled()) break;                 }             } else {                 log.d("articles: ", "null");             }          } catch (jsonexception e) {             e.printstacktrace();         }          return null;     }      protected void onpostexecute(string file_url) {          list.setscrollingcacheenabled(false);         adapter = new listuniadapter(getactivity(), unilist);         list.setadapter(adapter);          list.setonitemclicklistener(new adapterview.onitemclicklistener() {             @override             public void onitemclick(adapterview<?> arg0, view view, int arg2, long arg3) {  }         });      } } 

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