List box in MX2004, button works, setChangeHandler doesn't

1

I have this code on my actions frame:

function displayDetails(){
		display_box.text = drop_down_list.getSelectedItem().data;
	}
drop_down_list.setChangeHandler("displayDetails");

my listBox is named “drop_down_list” and my text field is named “display_box”

I have a button with this code:

on (press) {
	displayDetails();
}

when I press the button it works, when I just change the drop down item, nothing happens. The code looks just like the code in the tutorial, so I’m lost here.