Collisions never detected

Games
#1

There are obviously collisions happening on the screen, but my postCollision function never gets called. I create objects like this:

local cat = Cat.new()

The Cat class:

--constructor  
function new()  
 local obj = display.newImageRect("images/cat.png", 16, 16)  
  
 physics.addBody ( obj, "dynamic", {density = 1, friction = 1.0, bounce = 0.3} )  
  
 function obj:pCollision( obj, event )  
 print("collision") --this never gets printed  
 end  
  
 obj.postCollision = pCollision  
 obj:addEventListener( "postCollision", obj )  
 return obj  
end

What am I missing? [import]uid: 52127 topic_id: 9443 reply_id: 309443[/import]

#2

fixed: function pCollision( self, event ) [import]uid: 52127 topic_id: 9443 reply_id: 34615[/import]