! used in toggles

Question

Hi All,
Does anyone know about the use of the exclamation mark "!"
used in AS3, It's used as a toggle as in the following;
// Invoked when the mouse pointer moves over a text field.
private function mouseOverListener(e:MouseEvent):void{
// If the TextField's parent Sprite does not already contain
// the shape, then move it there.
DisplayObjectContainer.contains()
// returns true if the specified object is a descendant
// of the container.
if (!e.target.parent.contains(bgRect)){
e.target.parent.addChildAt(bgRect, 0);
But I cannot get my head around, how it acheives this, as in
how does this create or act as a toggle? Get me?
An easier example may suffice, anyone got any?
Sorry, if this seems rather a small problem, but it's Sunday;
on Sundays I study AS3. Maybe I've just worked through Moocks Book
to much ;) Hahahahahah
Kind Regards,
Boxing Boom

Answer 1

The ! operator inverts a Boolean value: meaning toggling
between true and false.
An example would be:
var theSkyIsBlue:Boolean == true;
trace(theSkyIsBlue); // true
theSkyIsBlue = !theSkyIsBlue;// changes theSkyIsBlue (which
is true at this point) to theSkyIsBlue = false
trace(theSkyIsBlue); // false
theSkyIsBlue = !theSkyIsBlue; //changes theSkyIsBlue (which
is false at this point) to theSkyIsBlue = true
trace(theSkyIsBlue); // traces true again - so the Boolean
value toggles between true and false
In your example, the contains() method of the parent of
e.target returns a Boolean value. Simply it says either yes, it's
true that the parent contains bgRect, or no, it's false, it doesn't
contain bgRect.
In this context the ! operator
(!e.target.parent.contains(bgRect)) can be considered equivalent
to:
if (e.target.parent.contains(bgRect) == false) ...
TS