android - How can I get checkboxes working in my listview? -

i've been trying follow tutorials/ posts on s.o on how checkbox working in listview. lots of stuff want first want position of item checked app crashes , nullpointerexception error.

the error (with more stuff below part) :

    java.lang.nullpointerexception @ com.example.chris.tutorialspoint.selectphonecontactadapter.getview(selectphonecontactadapter.java:104) 

and line 104 :

convertview.settag(v); 

but me looks i've been following tutorials , don't know how adapt these posts problem: getting nullpointerexception in custom listview , crash in listview @ abslistview.obtainview listactivity. can tell me wrong? worked until started experimenting these checkboxes.

here customadapter code, selectphonecontactadapter:

public class selectphonecontactadapter extends baseadapter {      //define list made out of selectphonecontacts , call thecontactslist     public list<selectphonecontact> thecontactslist;     //define array list made out of selectcontacts , call arraylist     private arraylist<selectphonecontact> arraylist;     boolean itemchecked[];     context _c;      //define viewholder hold our name , number info, instead of querying     // findviewbyid. makes listview run smoother     viewholder v;      public selectphonecontactadapter(final list<selectphonecontact> selectphonecontacts, context context) {         thecontactslist = selectphonecontacts;         _c = context;         this.arraylist = new arraylist<selectphonecontact>();         this.arraylist.addall(thecontactslist);         itemchecked = new boolean[thecontactslist.size()];      }       @override     public int getcount() {         system.out.println("the amount in arraylist :" + arraylist.size());         return arraylist.size();     }      @override     public object getitem(int i) {         return thecontactslist.get(i);     }      @override     public long getitemid(int i) {         return i;     }      @targetapi(build.version_codes.lollipop)      static class viewholder {         //        in each cell in listview show items want have //        having viewholder caches our ids, instead of having call , load each 1 again , again         textview title, phone;         checkbox check;     }      @override     public view getview(final int i, view convertview, viewgroup viewgroup) {          //we're naming our convertview view         view view = convertview;           if (view == null) {              v = new viewholder();             system.out.println("getview position :" + i);              //if there nothing there (if it's null) inflate view layout             layoutinflater li = (layoutinflater) _c.getsystemservice(context.layout_inflater_service);             view = li.inflate(r.layout.phone_inflate_listview, null);               //      so, example, title cast name id, in phone_inflate_listview, //        phone cast id called no etc             v.title = (textview) view.findviewbyid(r.id.name);             v.phone = (textview) view.findviewbyid(r.id.no);             v.check = (checkbox) view.findviewbyid(r.id.checkboxcontact);              convertview.settag(v);              //or else use view (what can see in each row) there         } else {             view = convertview;          }   //        store holder view         final selectphonecontact data = (selectphonecontact) thecontactslist.get(i);          //in listview contacts, set name         v.title.settext(data.getname());         //in listview contacts, set number         v.phone.settext(data.getphone());         v.check.setchecked(false);          v.check.setchecked(itemchecked[i]);          v.check                 .setoncheckedchangelistener(new compoundbutton.oncheckedchangelistener() {                     @override                     public void oncheckedchanged(compoundbutton buttonview,                                                  boolean ischecked) {                         itemchecked[i] = ischecked;                     }                 });          // return completed view render on screen         return view;       } } 

my getters , setters, selectphonecontact:

public class selectphonecontact {      string phone;      public string getphone() {return phone;}      public void setphone(string phone) {         this.phone = phone;     }      string name;      public string getname() {         return name;     }      public void setname(string name) {         this.name = name;     }      boolean selected;      public boolean isselected() {         return selected;     }      public void setselected(boolean selected){         this.selected=selected;     } } 

i can post more code if necessary.

consider code:

@override public view getview(final int i, view convertview, viewgroup viewgroup) {     ...     view view = convertview;      if (view == null) {         ...         view = li.inflate(r.layout.phone_inflate_listview, null);         ...         convertview.settag(v);     }     ... } 

first assign value of convertview view variable. when null, branch if statement, assign new value view via li.inflate().

however, reference convertview later inside if statement. despite fact wrote view = convertview above, @ point convertview still null.

there 2 ways fix this. first option change convertview.settag(v) view.settag(v). other delete line:

view view = convertview; 

and change place reference view use convertview instead. there's no need introduce new view view variable; can work convertview directly.