when I press a key to pop up a new window, how to forbid inputting into the edit control in the new window?

Hello,
I press a key like "A" as shortcut to pop up a new window with an input control and meantime set focus to the input control. After the new window pop up, the input control would show a "A" on it.
The code is as below:
private var dialog:Dialog=new Dialog();

private function OnKeyDown(event:KeyboardEvent):void
{
if (event.ctrlKey)

{ if(event.keyCode == 70) Show(); }

}

private function Show():void

{ PopUpManager.addPopUp(dialog, this, false); dialog.FindText.setFocus(); }

</mx:Script>

<mx:Form x="57" y="43" width="616" height="363" backgroundColor="#52EE9F">
<mx:TextArea id="textArea" keyDown="OnKeyDown(event);" width="584" height="327"/>
</mx:Form>

I am looking forward to your reply. Thank you.