add a checkbox inside a table

Hi for all,
I have in my table:

addContainerProperty(PROPERTY_active, CheckBox.class, null);

I want to modify the value of checkbox from a list.

boolean activ=true;
 for (User userp : list) {
 		            Item item = addItem(userp.getlogin());
 		       
 		        if(userp.getIsactive().equals("T")){
 		        	activ=true;
 		        }else{
 		        	activ=false;
 		        }
 		        
 		            item.getItemProperty(PROPERTY_active).setValue(activ);
 		        
 		           
 		       }

but it doesn't work.