如何使用TCPDF摆脱此错误："TCPDF ERROR: Some data has already been output to browser, can't send PDF file"

Question

我想打印输出（即变量$matter的值），但我收到上面提到的错误消息。我为它做了很多谷歌，并检查了php标签前后的空格。但无法得到解决方案。请帮助我。这是我使用 tcpdf 打印输出的代码：

<?php
    ob_start();
  require_once("../../includes/application-header.php");
  // Include tcpdf liabrary
  require_once OCN_ROOT."/core/extention/tcpdf/config/lang/eng.php";
  require_once OCN_ROOT."/core/extention/tcpdf/tcpdf.php";

    define ('PDF_MARGIN_TOP', 22); 
    define ('PDF_HEADER_TITLE', 'This is Heading');
    define ('PDF_HEADER_STRING', $head_string);
    define ('PDF_CREATOR', PAGE_TITLE); 
    // create new PDF document
    $pdf = new TCPDF(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false);
    // set document information
    $pdf->SetCreator(PDF_CREATOR);
    $pdf->SetAuthor(PDF_CREATOR);
    $pdf->SetTitle('TCPDF Example');
    // set default header data
    $pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, PDF_HEADER_TITLE, PDF_HEADER_STRING);
    // set header and footer fonts
    $pdf->setHeaderFont(Array(PDF_FONT_NAME_MAIN, '', PDF_FONT_SIZE_MAIN));
    $pdf->setFooterFont(Array(PDF_FONT_NAME_DATA, '', PDF_FONT_SIZE_DATA));
    // set default monospaced font
    $pdf->SetDefaultMonospacedFont(PDF_FONT_MONOSPACED);
    //set margins
    $pdf->SetMargins(PDF_MARGIN_LEFT, PDF_MARGIN_TOP, PDF_MARGIN_RIGHT);
    $pdf->SetHeaderMargin(PDF_MARGIN_HEADER);
    $pdf->SetFooterMargin(PDF_MARGIN_FOOTER);
    //set auto page breaks
    $pdf->SetAutoPageBreak(TRUE, PDF_MARGIN_BOTTOM);
    //set image scale factor
    $pdf->setImageScale(PDF_IMAGE_SCALE_RATIO);
    //set some language-dependent strings
    $pdf->setLanguageArray($l);
    // ---------------------------------------------------------
    // set font
    $pdf->SetFont('helvetica', '', 10);
    // add a page
    $pdf->AddPage();
    $matter = <<<EOD
         <h1>HTML Example</h1> 
EOD;
    $pdf->writeHTML($matter, true, false, true, false, '');
    // reset pointer to the last page
    $pdf->lastPage();
    // ---------------------------------------------------------
    ob_flush();
    //Close and output PDF document
    $pdf->Output('example_061.pdf', 'I');
    //============================================================+
    // END OF FILE                                                
    //============================================================+
?>

Answer 1

尝试而不是用ob_end_clean(); ob_flush();