package {
	import flash.display.MovieClip;
	import flash.events.Event;

	import fl.events.ComponentEvent; 
	import fl.controls.ComboBox;
	import fl.data.DataProvider; 




	public class AS3_combobox2 extends MovieClip {
		var comboData:Array = new Array( 
			{label:"Choice One", data:"one"}, 
			{label:"Choice Two", data:"two"}
		); 
		
		var combobox_cb:ComboBox = new ComboBox();

		public function AS3_combobox2() {
			combobox_cb.dropdownWidth = 210; 
			combobox_cb.width = 200;  
			combobox_cb.move(150, 50); 
			combobox_cb.prompt = "Make a Choice"; 
			combobox_cb.dataProvider = new DataProvider(comboData); 
			combobox_cb.addEventListener(Event.CHANGE, changeHandler); 
			 
			addChild(combobox_cb); 
		}
		public function changeHandler(event:Event):void { 
			// do something based on the selected item's value
			switch(combobox_cb.selectedItem.data) {
				case "one":
					trace("One was chosen!");
					break;
				case "two":
					trace("Two was chosen!");
					break;
			}
		}




	}
}

http://dl.dropbox.com/u/316550/code-AS3_combobox.zip

This is the most simple example of a ComboBox created in AS3, based mostly on Adobe's example from http://help.adobe.com/en_US/ActionScript/3.0_UsingComponentsAS3/WS5b3ccc516d4fbf351e63e3d118a9c65b32-7fa9.html

Inside the zip file you will find two folders. The first is this example with a ComboBox dragged onto the stage of the FLA with a supporting .AS file to populate it and make it work. The second example shows a ComboBox created and populated entirely by actionscript.

AS3 ComboBox extremely basic example

form, dropdown

ActionScript 3