Problem in FPDF header with a php variable

I have a php file that I use to print pdf (using FPDF). In this file I have a variable $date and I would like to show this variable $date in the header on each of the pages of my pdf document. That is my variable $date:

$convert_date=st开发者_运维知识库rtotime($selected_date);
global $date;
$date=date("d/m/Y",$convert_date);

And this is the class FPDF:

class PDF extends FPDF{

    function setDate($dat){
        $this->header_date = $dat;
    }

    function getDate(){
        return $this->header_date;
    }

    function Header(){
        $this->SetFont('Arial','B',16);
        $this->setDate($date);
        $this->Write (10, '       Date: '); //1° Write
        $this->Write (10, $this->getDate()); //2° Write NOT WORKING 
        $this->Ln();
    } ...

The problem is that the second $this->Write prints nothing.

I checked that if I call $this->setDate('abcd');, it prints "abcd" ok.

How can I pass this $date variable in my pdf header function?

I'm not sure because I've not used them in about five years, but don't you have to declare $date as being a global inside the Header() function?

function Header() {
    $date = $GLOBALS['date'];
    ...