如何在android中禁用网格视图中特定位置的项目点击

i am using a grid view in which i am using a text view for each cell. i am using onitemclick to perform some action when clicked on grid cell. i want to disable on item click for particular positions in grid view. how do i do that. i used convertView.setclickable(false) for particular position in getView which is giving null pointer exception. How do i do that?? here s my code.i am using a grid view in which i am using a te