I did not find a direct way but you can use this hack
module Shoes::Types
def centr
left=(self.parent.width-self.style[:width])/2
self.move(left,self.top)
end
def middle
top=(self.parent.height-self.style[:height])/2
self.move(self.left,top)
end
end
Shoes.app do
@c=stack :width=>50, :height=>30 do
a=list_box :items => ["lol","b"], :width => 50, :height=>30
end
@c.centr.middle
end
What is done is actually first to extend the functionality of slots so that you can place them in the center or middle of the containing slot. Then you wrap your listbox in a tiny slot, which you center.