android - ListView getting displayed, but App crashes on Scrolling and clicking -

i have listview custom layout named custom_listview.xml:

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <textview xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:textsize="20dp" android:padding="5dp" android:id="@+id/file_name" />  <textview     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:textsize="18dp"     android:id="@+id/file_path"/>  </linearlayout> 

and customadapter class:

public class customadapter extends baseadapter {  arraylist<file> result; context context;  private static layoutinflater inflater=null; public customadapter(activity parentactivity, arraylist<file> filelist) {     // todo auto-generated constructor stub     result=filelist;     context=parentactivity;    inflater = ( layoutinflater )context.             getsystemservice(context.layout_inflater_service); } @override public int getcount() {     // todo auto-generated method stub     return result.size(); }  @override public object getitem(int position) {     // todo auto-generated method stub     return position; }  @override public long getitemid(int position) {     // todo auto-generated method stub     return position; }  public class holder {     textview file_name;     textview file_path; } @override public view getview(final int position, view convertview, viewgroup parent) {     // todo auto-generated method stub        if (convertview == null)     {         layoutinflater minflater =   (layoutinflater)context.getsystemservice(context.layout_inflater_service);         convertview = minflater.inflate(r.layout.custom_listview, null);     }      holder holder=new holder();     holder.file_name=(textview) convertview.findviewbyid(r.id.file_name);     holder.file_path=(textview) convertview.findviewbyid(r.id.file_path);     //holder.img=(imageview) rowview.findviewbyid(r.id.imageview1);     holder.file_name.settext(result.get(position).getname());     holder.file_path.settext(result.get(position).getpath());      return convertview;     }      } 

and here onclicklistener listview:

 public void onitemclick(adapterview<?> parent, view view, int position,       long id) {       int color = color.transparent;     drawable background = parent.getchildat(position).getbackground();     if (background instanceof colordrawable)         color = ((colordrawable) background).getcolor();   if(color == color.cyan)   { parent.getchildat(position).setbackgroundcolor(color.transparent);}     else {       parent.getchildat(position).setbackgroundcolor(color.cyan);       textview t;       t = (textview) view.findviewbyid(r.id.file_path);       files_selected.addelement(t.gettext().tostring());        }       }       } 

the app works fine when click on item on top of list. scroll down , click item, app crashes. please help. thanks!

shouldnt be;

if (convertview == null) {    layoutinflater minflater =   (layoutinflater)context.getsystemservice(context.layout_inflater_service);    convertview = minflater.inflate(r.layout.custom_listview, null);     holder holder=new holder();    holder.file_name=(textview) convertview.findviewbyid(r.id.file_name);    holder.file_path=(textview) convertview.findviewbyid(r.id.file_path);    //holder.img=(imageview) rowview.findviewbyid(r.id.imageview1);    holder.file_name.settext(result.get(position).getname());    holder.file_path.settext(result.get(position).getpath()); }else{     viewholder = (viewholder) view.gettag();  }        view.settag(viewholder);