Unable to execute the sql query, only dispaying blank page.

<?php 
require('fpdf.php');
$today=date('d_m_Y');
$hostname = "localhost";
$database = "developer";
$username = "root";
$password = "";
$conn = mysql_connect($hostname, $username, $password) or die(mysql_error());
mysql_select_db($database, $conn);
class PDF_result extends FPDF {
    function __construct ($orientation = 'P', $unit = 'pt', $format = 'Letter', $margin = 40) {
        $this->FPDF($orientation, $unit, $format);
        $this->SetTopMargin($margin);
        $this->SetLeftMargin($margin);
        $this->SetRightMargin($margin);

        $this->SetAutoPageBreak(true, $margin);
    }

    function Header () {
      //   $this->Image('images/logo.png',100,15,200);
    //  $this->SetFont('Arial', 'B', 20);
    //  $this->SetFillColor(36, 96, 84);
    //  $this->SetTextColor(225);
        $this->Cell(0, 30, "PAYMENT DETAILS", 0, 1, 'C', true);
    }

 function Footer()
{
    //Position at 1.5 cm from bottom
    $this->SetY(-15);
    //Arial italic 8
    $this->SetFont('Arial','I',8);
    //Page number
    $this->Cell(0,10,'Generated at local server',0,0,'C');
}
function Generate_Table($i, $cardNo, $installmentAmount, $paymentDate) {

    $this->SetFont('Arial', 'B', 12);
    $this->SetTextColor(0);
//  $this->SetFillColor(94, 188, z);
$this->SetFillColor(94, 188, 225);
    $this->SetLineWidth(1);
    $this->Cell(30, 25, "Sno", 'LTR', 0, 'C', true);
    $this->Cell(120, 25, "Card No", 'LTR', 0, 'C', true);
    $this->Cell(100, 25, "Installment Amount", 'LTR', 0, 'C', true);
    $this->Cell(100, 25, "Paid Date", 'LTR', 0, 'C', true);

    $this->SetFont('Arial', '');
    $this->SetFillColor(238);
    $this->SetLineWidth(0.2);
    $fill = false;
}
    **function qry($qry)
{
    $this->$qry=mysql_query("SELECT cardNo, installmentAmount, paymentDate FROM payment order by cardNo",$this->$conn);
    if($this->$qry!=false)
{
    $i=1;
    while($this->$res=mysql_fetch_array($qry))
    {
        $myArr=array($i,$res['cardNo'],$res['installmentAmount'],$res['paymentDate']);
        $this->$i++;
    }**
}
}

    //for ($i = 0; $i < count($subjects); $i++) {
    //  $this->Cell(427, 20, $subjects[$i], 1, 0, 'L', $fill);
    //  $this->Cell(100, 20,  $marks[$i], 1, 1, 'R', $fill);
    //  $fill = !$fill;
    //}
    //$this->SetX(367);
    //$this->Cell(100, 20, "Total", 1);
//  $this->Cell(100, 20,  array_sum($marks), 1, 1, 'R');
}
$pdf = new PDF_result();
$pdf->AddPage();
$pdf->SetFont('Arial', 'B', 12);
$pdf->SetY(100);
$pdf->Cell(100, 13, "");
$pdf->SetFont('Arial', 'B');
$pdf->Cell(250, 13, $title);
$pdf->SetFont('Arial', 'B');
$pdf->Cell(50, 13, "Date:");
$pdf->SetFont('Arial','');
$pdf->Cell(100, 13, date('F j, Y'), 0, 1);
$pdf->SetFont('Arial', 'I');
$pdf->SetX(140);
//$pdf->Cell(200, 15, $_POST['e-mail'], 0, 2);
//$pdf->Cell(200, 15, $_POST['Address'] . ',' . $_POST['City'] , 0, 2);
//$pdf->Cell(200, 15, $_POST['Country'], 0, 2);
$pdf->Ln(100);
$pdf->Generate_Table($i, $cardNo, $installmentAmount, $paymentDate);
$pdf->Ln(50);
$message = "For More Information Contact us at : ";
$pdf->MultiCell(0, 15, $message);
$pdf->SetFont('Arial', 'U', 12);
$pdf->SetTextColor(1, 162, 232);
$pdf->Write(13, "support@domain.com", "support@domain.com");
$pdf->Output('result-.$today.pdf', 'F');
?>
function qry($qry)
{
    $this->res = mysql_query("SELECT cardNo, installmentAmount, paymentDate FROM payment order by cardNo", $conn);
    if ($this->res != false)
    {
        $i = 1;
        while ($this->res = mysql_fetch_array($qry))
        {
            $myArr = array($i, $this->res['cardNo'], $this->res['installmentAmount'], $this->res['paymentDate']);
            $i++;
        }
    }
}

$this->$conn is not valid. It should be $conn because you set it outside of your class instance. You REALLY need to check your OOP code, because you are using instance properties wrong (syntax).

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