android - How to get datepicker properties from dialogfragment -

hello have code

public class datetimepicker extends android.support.v4.app.dialogfragment  {   public interface datetimepickerlistener {        // public void ondialogpositiveclick(dialogfragment dialog);       //  public void ondialognegativeclick(dialogfragment dialog);         public void ondialogpositiveclick(android.app.dialogfragment dialog);         public void ondialognegativeclick(android.app.dialogfragment dialog);     }      // use instance of interface deliver action events    datetimepickerlistener mlistener;    datepicker dp;    timepicker tp;    int year;     @override    public dialog oncreatedialog(bundle savedinstancestate) {        alertdialog.builder builder = new alertdialog.builder(getactivity());        // layout inflater        layoutinflater inflater = getactivity().getlayoutinflater();        dp = (datepicker) this.getactivity().findviewbyid(r.id.date_picker);       //  tp = (timepicker) this.getview().findviewbyid(r.id.time_picker);        // inflate , set layout dialog        // pass null parent view because going in dialog layout        builder.setview(inflater.inflate(r.layout.date_time_picker, null))        // add action buttons               .setpositivebutton(r.string.set, new dialoginterface.onclicklistener() {                   @override                   public void onclick(dialoginterface dialog, int id) {                       // sign in user ...                     year = dp.getdayofmonth();                      stringbuilder sb = new stringbuilder();                    sb.append(year);              /*  int   day  = dp.getdayofmonth();              int   month= dp.getmonth()+1;              int   year = dp.getyear();               simpledateformat sdf = new simpledateformat("dd-mm-yyyy");              date dt = new date(day, month, year);               string formateddate = sdf.format(dt);*/               serviceactivity.tv.settext(sb.tostring());                    toast.maketext(getactivity().getbasecontext(), "you selected set button ",                             toast.length_long).show();                   }               })               .setnegativebutton(r.string.cansel, new dialoginterface.onclicklistener() {                   public void onclick(dialoginterface dialog, int id) {                       datetimepicker.this.getdialog().cancel();                   }               });           return builder.create();    }      // override fragment.onattach() method instantiate datetimepickerlistener     @override     public void onattach(activity activity) {         super.onattach(activity);         // verify host activity implements callback interface         try {             // instantiate noticedialoglistener can send events host             mlistener = (datetimepickerlistener) activity;         } catch (classcastexception e) {             // activity doesn't implement interface, throw exception             throw new classcastexception(activity.tostring()                     + " must implement datetimepickerlistener");         }     }      }  

when click on set button program crashes. tryed
dp = (datepicker) this.getview().findviewbyid(r.id.date_picker);

it crashes tried

dp = (datepicker) this.dialog.findviewbyid(r.id.date_picker); 

it crashes why wrong?

try code in oncreatedialog:

layoutinflater inflater = layoutinflater.from(getactivity()); view view = inflater.inflate(r.layout.date_time_picker, null ); dp = (datepicker) view.findviewbyid(r.id.datepicker); builder.setview(view, null))