android - Dealing with Fragment and listView and JSON -

i trying make application menudrawer contains 4 fragments. how application show do. when starts, should retrieve data website. retrieved data should in listview in first fragment. second fragment should contain webview view page in android device. third show text details. application crashes when first fragment gets details website. here code : fragment layout following:

my first fragment contains following:

<listview     android:layout_margintop="10dp"     android:layout_below="@+id/txtlabel"     android:layout_width="match_parent"     android:layout_height="300dp"     android:background = "@android:color/transparent"     android:padding="3dp"     android:dividerheight="1dp"     android:id="@+id/mlv"></listview> 

the first fragment called when app starts. have list adapter , list model worked well.

my main class contains inner class gets data. made model class , adapter class: here main code :

  public class mainactivity extends activity {  // declare properties private string[] mnavigationdraweritemtitles; private drawerlayout mdrawerlayout; private listview mdrawerlist; private listview mlistview; private listviewnewsadapter listviewnewsadapter; private arraylist<listviewnewsitem> listviewnewsitems;  private jsonparser jsonparser = new jsonparser();  private string readnews_url =         "xyz-myweb-xyz.com";   private actionbardrawertoggle mdrawertoggle;  // nav drawer title private charsequence mdrawertitle;  // used store app title private charsequence mtitle;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     mlistview = (listview) findviewbyid(r.id.mlv);        // proper titles     mtitle = mdrawertitle = gettitle();      // initialize properties     mnavigationdraweritemtitles = getresources().getstringarray(r.array.navigation_drawer_items_array);     mdrawerlayout = (drawerlayout) findviewbyid(r.id.drawer_layout);     mdrawerlist = (listview) findviewbyid(r.id.left_drawer);      // list drawer items     objectdraweritem[] draweritem = new objectdraweritem[4];      draweritem[0] = new objectdraweritem(r.drawable.home_icon, "home");     draweritem[1] = new objectdraweritem(r.drawable.website_icon, "website");     draweritem[2] = new objectdraweritem(r.drawable.ic_action_share, "help");      // pass folderdata our listview adapter     draweritemcustomadapter adapter = new draweritemcustomadapter(this, r.layout.listview_item_row, draweritem);      // set adapter list view     mdrawerlist.setadapter(adapter);      // set item click listener     mdrawerlist.setonitemclicklistener(new draweritemclicklistener());          // app icon control nav drawer     mdrawerlayout = (drawerlayout) findviewbyid(r.id.drawer_layout);     mdrawertoggle = new actionbardrawertoggle(             this,                  /* host activity */             mdrawerlayout,         /* drawerlayout object */             r.drawable.ic_drawer,  /* nav drawer icon replace 'up' caret */             r.string.drawer_open,  /* "open drawer" description */             r.string.drawer_close  /* "close drawer" description */             ) {          /** called when drawer has settled in closed state. */         public void ondrawerclosed(view view) {             super.ondrawerclosed(view);             getactionbar().settitle(mtitle);         }          /** called when drawer has settled in open state. */         public void ondraweropened(view drawerview) {             super.ondraweropened(drawerview);             getactionbar().settitle(mdrawertitle);         }     };      // set drawer toggle drawerlistener     mdrawerlayout.setdrawerlistener(mdrawertoggle);      // enable actionbar app icon behave action toggle nav drawer     getactionbar().setdisplayhomeasupenabled(true);     getactionbar().sethomebuttonenabled(true);        if (savedinstancestate == null) {         // on first time display view first nav item         selectitem(0);     } } 

the method deals fragments, it's inside mymainactivity :

     private void selectitem(int position) {      // update main content replacing fragments      fragment fragment = null;      switch (position) {     case 0:         fragment = new createfragment();         new getnewstask().execute();         break;     case 1:          fragment = new readfragment();         break;     case 2:         fragment = new helpfragment();         break;      default:         break;     }      if (fragment != null) {         fragmentmanager fragmentmanager = getfragmentmanager();         fragmentmanager.begintransaction().replace(r.id.content_frame, fragment).commit();         // update selected item , title, close drawer         mdrawerlist.setitemchecked(position, true);         mdrawerlist.setselection(position);         settitle(mnavigationdraweritemtitles[position]);         mdrawerlayout.closedrawer(mdrawerlist);      } else {         // error in creating fragment         log.e("mainact10ity", "error in creating fragment");     }  }  

i used inner class retrieve data web:

  private class getnewstask extends asynctask<void, void, boolean> {     private progressdialog mprogressdialog;      private jsonobject jsonobjectresult = null;      private string error;      @override     protected void onpreexecute()     {         super.onpreexecute();         listviewnewsitems = new arraylist<listviewnewsitem>();         mprogressdialog = progressdialog.show(mainactivity.this,                 "processing...", "get last news", false, false);     }      @override     protected boolean doinbackground(void... params)     {         jsonobjectresult = jsonparser.makehttprequest(readnews_url, null);          if (jsonobjectresult == null)         {             error = "error in connection";             return false;         }          try         {             if (jsonobjectresult.getint("success") == 1)             {                 jsonarray jsonarray = jsonobjectresult.getjsonarray("posts");                 (int = 0; < jsonarray.length(); i++)                 {                     jsonobject news = jsonarray.getjsonobject(i);                      listviewnewsitem listviewnewsitem = new listviewnewsitem                             (                                     news.getstring("title"),                                     news.getstring("type")                             );                     listviewnewsitems.add(listviewnewsitem);                 }                 return true;             }             else                 error = jsonobjectresult.getstring("message");          }         catch (exception ex)         {          }          return false;     }      @override     protected void onpostexecute(boolean aboolean)     {         super.onpostexecute(aboolean);         mprogressdialog.dismiss();         if (aboolean)         {             listviewnewsadapter = new listviewnewsadapter(getapplicationcontext(),                     listviewnewsitems);             mlistview.setadapter(listviewnewsadapter);         }         else             toast.maketext(getapplicationcontext(), error, toast.length_long).show();     } } 

where have use

new getnewstask().execute(); 

i tried use in oncreate, app crashed. tried use inside switch app crashes. have idea how fix ?

i fixed following: moving followings fragment :

 private listview mlistview; private listviewnewsadapter listviewnewsadapter; private arraylist<listviewnewsitem> listviewnewsitems;  private jsonparser jsonparser = new jsonparser();  private string readnews_url =         "xxxxxxxx.xxxxx.xxxxx";   public createfragment() {     // required empty public constructor } 

then, inside oncreateview created :

mlistview = (listview) rootview.findviewbyid(r.id.mlv);

    new getnewstask().execute(); 

after that, wrote inner class fragment. well, had change arguments make code work well. then, run , it's working property now. thank