actionscript-3 - as3ベクトルで検索するにはどうすればよいですか

Question

indexOf を使用して配列で検索できますが、ベクトルは機能しません

import flash.events.KeyboardEvent;

var characters:Vector.<String >  = Vector.<String > (["abcdef".split("")]);
trace(characters);

txt.restrict = characters.toString();
txt.addEventListener(KeyboardEvent.KEY_DOWN,search);
function search(event:KeyboardEvent):void
{
    var i:int = characters.indexOf(String.fromCharCode(event.charCode));
    trace("key press= "+String.fromCharCode(event.charCode),"indexOf search ="+i);
}

出力

a,b,c,d,e,f
key press= a indexOf search =-1