Variable error within the function

I'm having problems and from what I searched the internet forums, others have the same doubt as me.

I can not use PHP variables within the transaction function. How do I set a variable?

For example, this does not work:

$id = $_POST["id_saida"];
$nome = $_POST["nome_produto"];
$valor   = $_POST["valor_final"];


class CreatePaymentRequestLightbox
{
public static function main()
{

Original:

$paymentRequest->addItem('0001', 'Notebook prata', 1, 430.00); //original

How would you like it to work:

$paymentRequest->addItem($id, $nome, $n, $valor); // como gostaria

Only that gives error, comes empty. What to do?

<?php

require_once "includes/ps/PagSeguroLibrary/PagSeguroLibrary.php";
$form = $_GET['form'];
if ($form == "pagseg"){
echo "ok";
$id_transfer = $_POST["id_transfer"];
$id = $_POST["id_saida"];
$nome = $_POST["nome_produto"];
$valor   = $_POST["valor_final"];

$v1 ="teste";

/**
* Class with a main method to illustrate the usage of the domain class     
PagSeguroPaymentRequest
*/
class CreatePaymentRequestLightbox
{
    public static function main()
    {
        // Instantiate a new payment request
        $paymentRequest = new PagSeguroPaymentRequest();

        // Set the currency
        $paymentRequest->setCurrency("BRL");

        // Add an item for this payment request
        $paymentRequest->addItem($v1, 'Notebook prata', 1, 430.00);

        // Set a reference code for this payment request, it is useful to identify this   
      payment
        // in future notifications.
        $paymentRequest->setReference("REF123");

        // Set shipping information for this payment request
        $sedexCode = PagSeguroShippingType::getCodeByType('SEDEX');
        $paymentRequest->setShippingType($sedexCode);
        $paymentRequest->setShippingAddress(
            '01452002',
            'Av. Brig. Faria Lima',
            '1384',
            'apto. 114',
            'Jardim Paulistano',
            'São Paulo',
            'SP',
            'BRA'
        );

        // Set your customer information.
        $paymentRequest->setSender(
            'João Comprador',
            '[email protected]',
            '11',
            '56273440',
            'CPF',
            '156.009.442-76'
        );

        // Set the url used by PagSeguro to redirect user after checkout process ends
        $paymentRequest->setRedirectUrl("http://www.lojamodelo.com.br");

        // Add checkout metadata information
        $paymentRequest->addMetadata('PASSENGER_CPF', '15600944276', 1);
        $paymentRequest->addMetadata('GAME_NAME', 'DOTA');
        $paymentRequest->addMetadata('PASSENGER_PASSPORT', '23456', 1);

        // Another way to set checkout parameters
        $paymentRequest->addParameter('notificationURL', 'http://www.lojamodelo.com.br/nas');
        $paymentRequest->addParameter('senderBornDate', '07/05/1981');
        $paymentRequest->addIndexedParameter('itemId', '0003', 3);
        $paymentRequest->addIndexedParameter('itemDescription', 'Notebook Preto', 3);
        $paymentRequest->addIndexedParameter('itemQuantity', '1', 3);
        $paymentRequest->addIndexedParameter('itemAmount', '200.00', 3);

        try {

            /*
             * #### Credentials #####
             * Replace the parameters below with your credentials
             * You can also get your credentials from a config file. See an example:
             * $credentials = PagSeguroConfig::getAccountCredentials();
             */

            // seller authentication
            $credentials = new PagSeguroAccountCredentials("[email protected]",
                "EDC2E4A8E6B246D29C713FB97C26808E");

            // application authentication
            //$credentials = PagSeguroConfig::getApplicationCredentials();

            //$credentials->setAuthorizationCode("E231B2C9BCC8474DA2E260B6C8CF60D3");

            // Register this payment request in PagSeguro to obtain the checkout code
            $onlyCheckoutCode = true;
            $code = $paymentRequest->register($credentials, $onlyCheckoutCode);

            self::printPaymentUrl($code);
        } catch (PagSeguroServiceException $e) {
            die($e->getMessage());
        }
      }

      public static function printPaymentUrl($code)
      {
        if ($code) {
            echo "<h2>Criando requisi&ccedil;&atilde;o de pagamento</h2>";
            echo "<p>Code: <strong>$code</strong></p>";
            echo "<script>
            PagSeguroLightbox('".$code."');
                  </script>";

        }
      }
     }
}
CreatePaymentRequestLightbox::main();