android - Adapter converView sometimes null -

i have listview , adapter. simple getview code found below.

public view getview(final int position, view convertview, viewgroup parent) {     if (convertview == null) {         log.d("mzule", "convertview null " + position);         convertview = minflater.inflate(r.layout.item_cheap_layout, null);     }     return convertview; } 

when build , run app. got logs below.

d/mzule   (25020): converview null 0 d/mzule   (25020): converview null 1 d/mzule   (25020): converview null 2 d/mzule   (25020): converview null 3 d/mzule   (25020): converview null 4 d/mzule   (25020): converview null 5 d/mzule   (25020): converview null 16 d/mzule   (25020): converview null 32 d/mzule   (25020): converview null 47 d/mzule   (25020): converview null 38 

it obvious previous 6 converviews null. not figure out why 16th, 32nd, 47th , 38th convertview null. make listview laggy.

take @ here. explaination how listview's recycling mechanism works.