Problem to move a MC on foreground

i've a problem to a set a different child index of a Movieclip. This is the code:

function processMusica():void
{

    var loadStatus:int=0
    var lastHeight:int=0

    for (var m=0; m < myXML.BLADE[sup].child("brano").length(); m++)
    {
       var titolobrano:TextField=new TextField  
       bladearray[sup].contenitore.addChild(titolobrano)
       titolobrano.text=myXML.BLADE[sup].brano[loadStatus].titolo

       lastHeight=titolobrano.height
       titolobrano.doubleClickEnabled=true
       titolobrano.addEventListener(MouseEvent.DOUBLE_CLICK, riproducibrano)
       loadStatus+=1   
    }

    if (isPlaying==false)
    {
       var riproduzioneDetails:MovieClip=new MovieClip
       riproduzioneDetails.name="riproduzioneDetails"
       var artista:TextField=new TextField
       artista.name="artista"
       bladearray[sup].contenitore.addChild(riproduzioneDetails)
       riproduzioneDetails.x=475
       riproduzioneDetails.addChild(artista)

    }
    setChildIndex(bladearray[sup].contenitore.riproduzioneDetails, bladear开发者_StackOverflow中文版ray[sup].contenitore.numChildren-1) //<------ PROBLEM HERE!

I want to move "riproduzioneDetails" MC on foreground, but when i attempt to launch application, it give me this error: TypeError: Error #2007: Parameter child must be non-null

I can see two potential problems, but it is hard to say because all the variables are not declared in your code. There may be a problem with your test condition:

if (isPlaying==false)
{
  ...
}

If "isPlaying" is true, your object "riproduzioneDetails" is never created, so of course it will be null. You have to create your object outside the "if" condition, before testing "isPlaying".

Another potential problem is the way you access your object, with "bladearray[sup].contenitore.riproduzioneDetails". As you used the "addChild" method to store your object, there should logically be a kind of "getChild" method. For instance,

setChildIndex(bladearray[sup].contenitore.getChildByName("riproduzioneDetails"),bladearray[sup].contenitore.numChildren-1)

... may be better.