android - Parsing JSONArray and populating it in a ListView -

following activity supposed take values (users) json, , put them in arraylist<user> user class created. after doing supposed fill listview these values. problem every time try open activity, crashes.

can please tell me problem? , class works purpose want?

public class search extends appcompatactivity {      @override      protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);           setcontentview(r.layout.activity_search);       }      public void onclick(view v) {          switch (v.getid()){             case r.id.imagebutton2: new storeuserdataasynctask().execute();                 break;              }      }     @override     public boolean oncreateoptionsmenu(menu menu) {          // inflate menu; adds items action bar if present.        getmenuinflater().inflate(r.menu.menu_searchh, menu);        return true;     }     @override     public boolean onoptionsitemselected(menuitem item) {     // handle action bar item clicks here. action bar     // automatically handle clicks on home/up button, long     // specify parent activity in androidmanifest.xml.     int id = item.getitemid();      //noinspection simplifiableifstatement     if (id == r.id.action_settings) {           return true;     }            return super.onoptionsitemselected(item);     }       arraylist<user> userlist1=null;       public class storeuserdataasynctask extends asynctask<void,void,arraylist<user>> {      user user;      getusercallback usercallback;       progressdialog progressdialog;      spinner s11 = (spinner) findviewbyid(r.id.spinner);      spinner s2 = (spinner) findviewbyid(r.id.spinner2);      string bloodd = s11.getselecteditem().tostring();      string loc = s2.getselecteditem().tostring();       protected arraylist<user> doinbackground(void... params) {       user returneduser=null;      arraylist<user> userlist=null;      final int connection_timeout = 1000 * 15;      final string server_address = "http://xxxxx.comli.com/";      arraylist<namevaluepair> datatosend = new arraylist<>();      datatosend.add(new basicnamevaluepair("bloodtype", bloodd));      datatosend.add(new basicnamevaluepair("location", loc));       httpparams httprequestparams = new basichttpparams();      httpconnectionparams.setconnectiontimeout(httprequestparams, connection_timeout);      httpconnectionparams.setsotimeout(httprequestparams, connection_timeout);       httpclient client = new defaulthttpclient(httprequestparams);      httppost post = new httppost(server_address + "/search.php");       try {          post.setentity(new urlencodedformentity(datatosend));          httpresponse httpresponse = client.execute(post);           httpentity entity = httpresponse.getentity();          string result = entityutils.tostring(entity);          jsonobject jobject = new jsonobject(result);           if (jobject.length() == 0) {              userlist = null;              context context = getapplicationcontext();              charsequence text = "no available donor!";              int duration = toast.length_short;            } else {              string resultt = entityutils.tostring(entity);              jsonarray jsonarray = new jsonarray(resultt);              (int = 0; < jsonarray.length(); i++) {                      jsonobject jsonobject = jsonarray.getjsonobject(i);                      string fname = jsonobject.getstring("firstname");                      string lname = jsonobject.getstring("lastname");                      string blood = jsonobject.getstring("blood");                      string location = jsonobject.getstring("location");                      string email = jsonobject.getstring("email");                      string age = jsonobject.getstring("age");                      string password = jsonobject.getstring("password");                      string phone = jsonobject.getstring("phone");                      int agee = integer.parseint(age);                      int phonee = integer.parseint(phone);                       returneduser = new user(fname, lname, blood, location, email, password, agee, phonee);                      userlist.add(returneduser);                   }                 }               } catch (exception e) {                 e.printstacktrace();             }             userlist1=userlist;             return userlist;                    }          protected void onpostexecute(arraylist<user> avoid) {          progressdialog.dismiss();          displaycountrylist();         }      }       private void displaycountrylist(){      mycustomadapter dataadapter = null;      try {               //create arrayadaptar string array               dataadapter = new mycustomadapter(this,               r.layout.listv, userlist1);              listview listview = (listview) findviewbyid(r.id.listview);         // assign adapter listview               listview.setadapter(dataadapter);          //enables filtering contents of given listview               listview.settextfilterenabled(true);          }          catch (exception e) {              e.printstacktrace();          }      }         class mycustomadapter extends arrayadapter<user> {           private arraylist<user> userlist;           public mycustomadapter(context context, int textviewresourceid,                            arraylist<user> userlist) {             super(context, textviewresourceid, userlist);             this.userlist = new arraylist<user>();             this.userlist.addall(userlist);           }           private class viewholder {            textview name;            textview phone;            textview email;          }           @override          public view getview(int position, view convertview, viewgroup parent) {               viewholder holder = null;              log.v("convertview", string.valueof(position));              if (convertview == null) {                   layoutinflater vi = (layoutinflater)getsystemservice(                         context.layout_inflater_service);                  convertview = vi.inflate(r.layout.listv, null);                   holder = new viewholder();                  holder.name = (textview) convertview.findviewbyid(r.id.textview31);                  holder.phone = (textview) convertview.findviewbyid(r.id.textview33);                  holder.email = (textview) convertview.findviewbyid(r.id.textview34);                   convertview.settag(holder);              } else {                 holder = (viewholder) convertview.gettag();              }              user user = userlist.get(position);             holder.name.settext(user.getfirstname());             holder.phone.settext(user.getphone());             holder.email.settext(user.getemail());             return convertview;         }       }     }