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RangeError: Error #2006: The supplied index is out of bounds.

A problem I've run across a couple of times when moving a component from one parent to another is the following error:

RangeError: Error #2006: The supplied index is out of bounds.
	at flash.display::DisplayObjectContainer/getChildAt()
	at mx.core::Container/getChildAt()
	at mx.containers.utilityClasses::CanvasLayout/measure()
	at mx.containers::Canvas/mx.containers:Canvas::measure()
	(... some of stack trace deleted ...)
	at mx.core::UIComponent/mx.core:UIComponent::callLaterDispatcher2()
	at mx.core::UIComponent/mx.core:UIComponent::callLaterDispatcher()
	at [renderEvent]
	at [mouseEvent]

You'll notice that the stack trace is nothing but framework code. An error in a callLater that I didn't make? The problem is simple. When moving a component from one parent to another you have to call removeChild() on the current parent before calling addChild() to attach it to the new parent.

The following code demonstrates the issue:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical">
<mx:Script>
<![CDATA[
private var goToBob:Boolean = true;
private function swap():void
{
    if (goToBob)
    {
        // uncomment both removeChild() calls to prevent the error
        // alice.removeChild(aButton);
        bob.addChild(aButton);
    }
    else
    {
        // uncomment both removeChild() calls to prevent the error
        // bob.removeChild(aButton);
        alice.addChild(aButton);
    }
    goToBob = !goToBob;
}
]]>
</mx:Script>
<mx:Label text="Clicking the Swap button twice will cause a RangeError: Error #2006"/>
<mx:Canvas id="alice">
<mx:Button id="aButton" label="Swap" click="swap();"/>
</mx:Canvas>
<mx:Canvas id="bob">
</mx:Canvas>
</mx:Application>

As noted in the code comments, if you first call removeChild() the error goes away. While it would be nice if the framework let to just move a component in a single step, I seem to remember seeing in the documentation that the need to call remove before add is explained.

Comments

You da man! This was driving me nuts... seems a little strange though, since the initial swap seemed to be removing the child automatically... I didn't have problems until I tried to swap it back. Thanks for posting this!
Thanks, now its much clear to me ;-) Keep up the good work !!
Great post, you saved me!
Thanks for shedding light into my code ; ) ...
awesome, you saved me 3 hours of frustration!
Mate.. i would really love to thank you.. the solution which is provided by you is simply great... I was also facing the same issue.. but after seeing the solution provided by you.. i was able to solve the issue in my project.. Thanks..
I love u man~facing the same issue...
Hello, I am new in flex, I have problem with RangeError: Index '-1' specified is out of bounds. bellow is my code if(newValue == 0 || newValue

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