android - DatePickerFragment an cleaning project -

i have datepickerfragment in android project:

public class uses extends fragmentactivity {   @override public void oncreate(bundle savedinstancestate) {     //code  }  public class parkinglisthttp extends asynctask<string, void, string> {       //code     }      @override     protected void onpostexecute(string result) {           //code }  public void returnuses(string date) {      //code  }  public void selectdate(view v) {     dialogfragment newfragment = new datepickerfragment();     newfragment.show(getsupportfragmentmanager(), "datepicker"); }  public class datepickerfragment extends dialogfragment implements datepickerdialog.ondatesetlistener {      @override     public dialog oncreatedialog(bundle savedinstancestate) {         // use current date default date in picker         final calendar c = calendar.getinstance();         int year = c.get(calendar.year);         int month = c.get(calendar.month);         int day = c.get(calendar.day_of_month);          // create new instance of datepickerdialog , return         return new datepickerdialog(getactivity(), this, year, month, day);     }      public void ondateset(datepicker view, int year, int month, int day) {         // date chosen user         string datetext = context.getstring(r.string.date_name);         string[] strdays = new string[]{"dom", "lun", "mar", "mie", "jue", "vie", "sáb"};          final calendar c = calendar.getinstance();          c.set(calendar.year, year);         c.set(calendar.month, month-1);         c.set(calendar.day_of_month, day);          int week = c.get(calendar.day_of_week);           date.settext(datetext.replacefirst("\\*",strdays[week - 1] + " " + day + "/" + (month+1)+"/"+year));         returnuses(year+"-"+(month+1)+"-"+day);     } } 

}

when change code in project line

public class datepickerfragment extends dialogfragment implements datepickerdialog.ondatesetlistener { 

returns error:

 fragment inner class should static (com.usualbike.mandemo.uses.datepickerfragment) 

but it's solved cleaning project.

how can avoid error+cleaning?