Explanation of addChild and removeChild?

Question

Hi
I'm having trouble getting my head around using removeChild.
For example, I have a function that is triggered by a button click.  This function loads an external swf.  I then set a global variable swfLoaded to true, with the idea of having an if condition that executes removeChild(loader) if swfLoaded is true.
When trying to execute removeChild(loader), I get an error telling me that it must be the child of the caller.
I've seen the code below, which loads a default swf, but I don't want a default swf - I just want one loaded if the button is clicked, and then if another button is clicked, the original one to be removed before the next swf is loaded.
Can someone please explain to me why removeChild(loader) only works if addChild(loader) was originally executed outside of the function (like below)?
How do I make this code work without loading a default swf, just loading one once someone clicks a button, and then removing it?
var Xpos:Number = 110;
var Ypos:Number = 180;
var swf:MovieClip;
var loader:Loader = new Loader();
var defaultSWF:URLRequest = new URLRequest("swfs/eyesClosed.swf");
loader.load(defaultSWF);
loader.x = Xpos;
loader.y = Ypos;
addChild(loader);
// Btns Universal function
function btnClick(event:MouseEvent):void {
removeChild(loader);
var newSWFRequest:URLRequest = new URLRequest("swfs/" + event.target.name + ".swf");
loader.load(newSWFRequest);
loader.x = Xpos;
loader.y = Ypos;
addChild(loader);
// Btn listeners
eyesClosed.addEventListener(MouseEvent.CLICK, btnClick);
stingray.addEventListener(MouseEvent.CLICK, btnClick);
demon.addEventListener(MouseEvent.CLICK, btnClick);
strongman.addEventListener(MouseEvent.CLICK, btnClick);
Cheers
Shaun

Answer 1

Oh, I just did not pay enough attention to your code.
The way you wrote it - you don' have to remove it every time. A better approach is to add it only once and in subsequent calls to unload it:
var loader:Loader = new Loader();
// add it once
addChild(loader);
function btnClick(event:MouseEvent):void {
     // don't need this
     //removeChild(loader);
     // unload previously loaded content
     loader.unload();
     var newSWFRequest:URLRequest = new URLRequest("swfs/" + event.target.name + ".swf");
     loader.load(newSWFRequest);
     loader.x = Xpos;
     loader.y = Ypos;
     // don't need this either
     // addChild(loader);
Also, in Flash 10 it is better to use loader.unloadAndStop()