Add a function to slidetoggle just when open

Add a function to slidetoggle just when open

Hi I just make a div that shows a Map on Google, where you set cordinates
etc, anyway first problem was when animating height, the map inside have
this problem on size :
how to deal with google map inside of a hidden div (Updated picture)
I fix it just like the first answer calling initialize(); in my
slideToggle this fix the size issue.. The problem is that initialize();
takes the same time as the slideToggle so i lose the height animation, it
just dissapear,
IS there anyway to tigger initialize(); just when slidetoggle Open the div?
<script>
$('.dropdownmap').click(function(){
$('#mapDisplayWrap').slideToggle();
initialize();
})
</script>