DOM e XML

[starcraftworld]

Ho il file XML:

<?xml version="1.0"?>
<chess>
<board>
<id>123</id>
<develope>false</develope>
<move></move>
</board>
</chess>

Ho la seguente classe xml.php:

<?php

class Xml {

    public $file;
    public $fp;
    public $dom;
    public $xml;
    
    public function __construct ($file) {
        $this->file=$file;
        $this->fp=fopen($file,"r+");
        $this->dom=new DOMDocument();
        $this->xml="";
    } //__construct
    
    public function lock () {
        if (flock($this->fp,LOCK_EX))
            return true;
        return false;
    } //lock
    
    public function unlock () {
        flock($this->fp,LOCK_UN);
    } //unlock    
    
    public function load () {
        $this->xml=fread($this->fp,filesize($this->file));
        $this->dom->loadXML($this->xml);
    } //load
    
    public function save () {
        $this->xml=$this->dom->saveXML();
        fseek($this->fp,0,SEEK_SET);
        fwrite($this->fp,$this->xml);
        ftruncate($this->fp,ftell($this->fp));
    } //save
    
    public function close () {
        fclose($this->fp);
    } //close
    
    public function getValue ($node) {
        return $node->nodeValue;
    } //getValue
    
    public function getUndevelopedBoard () {
        $board=$this->dom->getElementsByTagName("board"); 
        foreach ($board as $board)
            if ($board->getElementsByTagName("develope")->item(0)->nodeValue=="false")
                return $board->getElementsByTagName("id")->item(0);
        return false;
    } //getUndevelopedBoard
    
    public function createNewBoard ($id) {
        $root=$this->dom->documentElement;
        $board=$this->dom->createElement("board");
        $id=$this->dom->createElement("id",$id);
        $board->appendChild($id);
        $develope=$this->dom->createElement("develope","false");
        $board->appendChild($develope);
        $move=$this->dom->createElement("move","");
        $board->appendChild($move);
        $root->appendChild($board); 
    } //createNewBoard
    
    public function addMove ($board, $idMove) {
        $move=$this->dom->createElement("id",$idMove);
        $moves=$board->getElementsByTagName("move");
        //
        var_dump($moves);
        //
        $moves->appendChild($move);
    } //addMove
    
    public function existBoard ($id) {
        $board=$this->dom->getElementsByTagName("board");
        foreach ($board as $board)
            if ($board->getElementsByTagName("id")->item(0)->nodeValue==$id)
                return true;
        return false;
    } //existBoard

} //Xml

?>

Ora eseguo il seguente codice:

<?php

include("xml.php");
include("chess.php");
include("chessboard.php");

$xml=new Xml('chess.xml');
if ($xml->lock()) {
    $xml->load();    
    $undevelopedBoard=$xml->getUndevelopedBoard();
    $undevelopedBoardValue=$xml->getValue($undevelopedBoard);
    if ($undevelopedBoard!=false) {
        $chessboard=new Chessboard($undevelopedBoardValue);
        $chessboard->mount();
        for ($i=0;$i<8;$i++)
            for ($j=0;$j<8;$j++)
                if ($chessboard->chessboard[$i][$j]->getRank()!="EMPTYBOX")
                    if ($chessboard->chessboard[$i][$j]->color==$chessboard->turn)
                        for ($m=0;$m<8;$m++)
                            for ($n=0;$n<8;$n++) {
                                $chessboard->cloneBoard();
                                if ($chessboard->chessboard[$i][$j]->move($m,$n,$chessboard->chessboard,$chessboard->board))
                                    if($chessboard->check($chessboard->turn)==false) {
                                        $chessboard->unmount();
                                        $xml->addMove($undevelopedBoard,$chessboard->output);
                                        if ($xml->existBoard($chessboard->output)==false) {
                                            $xml->createNewBoard($chessboard->output);
                                        } //if
                                    } //if
                            } //for

    } //if
    $xml->save();
    $xml->unlock();
    $xml->close();
} //if

?>

Ma produce l'output:

object(DOMNodeList)#72 (0) { }
Fatal error: Call to undefined method DOMNodeList::appendChild() on line 73 (file xml.php)

Dove sta il problema?