PS：这个previous_post没有关系，也无济于事。
我正在使用FPDF库，我正在尝试实现Header（）方法。我在类中添加了2个受保护的变量，并修改了构造函数以接受将设置它们的值。但是，当我尝试从Header（）方法访问这些变量时，我得到了＆＃39;致命错误：无法访问空房产＆＃34;。 我不知道我做错了。这让我发疯了。
我在代码中所做的只是：
$pdf = new FPDF("Hello", "Whatever");
$pdf->AliasNbPages();
$pdf->AddPage() //this method calls the Header() method , and it get called many times through the code
FPDF类如下：
完整代码： fpdf library（下载并获取V1.81）
标题方法：（上述属性为$ headerLeft）
function Header()
{
$this->Cell(30,10, $this->$headerLeft);
$this->Ln();
$this->SetFont('Arial','B',15);
// Move to the right
$this->Cell(80);
// Title
$this->Cell(30,10, $this->$headerRight);
// Line break
$this->Ln(20);
}
字段和构造函数：
class FPDF
{
protected $page; // current page number
protected $n; // current object number
protected $offsets; // array of object offsets
protected $buffer; // buffer holding in-memory PDF
protected $pages; // array containing pages
protected $state; // current document state
protected $compress; // compression flag
protected $k; // scale factor (number of points in user unit)
protected $DefOrientation; // default orientation
protected $CurOrientation; // current orientation
protected $StdPageSizes; // standard page sizes
protected $DefPageSize; // default page size
protected $CurPageSize; // current page size
protected $CurRotation; // current page rotation
protected $PageInfo; // page-related data
protected $wPt, $hPt; // dimensions of current page in points
protected $w, $h; // dimensions of current page in user unit
protected $lMargin; // left margin
protected $tMargin; // top margin
protected $rMargin; // right margin
protected $bMargin; // page break margin
protected $cMargin; // cell margin
protected $x, $y; // current position in user unit
protected $lasth; // height of last printed cell
protected $LineWidth; // line width in user unit
protected $fontpath; // path containing fonts
protected $CoreFonts; // array of core font names
protected $fonts; // array of used fonts
protected $FontFiles; // array of font files
protected $encodings; // array of encodings
protected $cmaps; // array of ToUnicode CMaps
protected $FontFamily; // current font family
protected $FontStyle; // current font style
protected $underline; // underlining flag
protected $CurrentFont; // current font info
protected $FontSizePt; // current font size in points
protected $FontSize; // current font size in user unit
protected $DrawColor; // commands for drawing color
protected $FillColor; // commands for filling color
protected $TextColor; // commands for text color
protected $ColorFlag; // indicates whether fill and text colors are different
protected $WithAlpha; // indicates whether alpha channel is used
protected $ws; // word spacing
protected $images; // array of used images
protected $PageLinks; // array of links in pages
protected $links; // array of internal links
protected $AutoPageBreak; // automatic page breaking
protected $PageBreakTrigger; // threshold used to trigger page breaks
protected $InHeader; // flag set when processing header
protected $InFooter; // flag set when processing footer
protected $AliasNbPages; // alias for total number of pages
protected $ZoomMode; // zoom display mode
protected $LayoutMode; // layout display mode
protected $metadata; // document properties
protected $PDFVersion; // PDF version number
protected $headerLeft;
protected $headerRight;
/*******************************************************************************
* Public methods *
*******************************************************************************/
function __construct($hLeft, $hRight, $orientation='P', $unit='mm', $size='A4')
{
// Some checks
$this->_dochecks();
// Initialization of properties
$this->headerLeft = $hLeft;
$this->headerRight = $hRight;
$this->state = 0;
$this->page = 0;
$this->n = 2;
$this->buffer = '';
$this->pages = array();
$this->PageInfo = array();
$this->fonts = array();
$this->FontFiles = array();
$this->encodings = array();
$this->cmaps = array();
$this->images = array();
$this->links = array();
$this->InHeader = false;
$this->InFooter = false;
$this->lasth = 0;
$this->FontFamily = '';
$this->FontStyle = '';
$this->FontSizePt = 12;
$this->underline = false;
$this->DrawColor = '0 G';
$this->FillColor = '0 g';
$this->TextColor = '0 g';
$this->ColorFlag = false;
$this->WithAlpha = false;
$this->ws = 0;
// Font path
if(defined('FPDF_FONTPATH'))
{
$this->fontpath = FPDF_FONTPATH;
if(substr($this->fontpath,-1)!='/' && substr($this->fontpath,-1)!='\\')
$this->fontpath .= '/';
}
elseif(is_dir(dirname(__FILE__).'/font'))
$this->fontpath = dirname(__FILE__).'/font/';
else
$this->fontpath = '';
// Core fonts
$this->CoreFonts = array('courier', 'helvetica', 'times', 'symbol', 'zapfdingbats');
// Scale factor
if($unit=='pt')
$this->k = 1;
elseif($unit=='mm')
$this->k = 72/25.4;
elseif($unit=='cm')
$this->k = 72/2.54;
elseif($unit=='in')
$this->k = 72;
else
$this->Error('Incorrect unit: '.$unit);
// Page sizes
$this->StdPageSizes = array('a3'=>array(841.89,1190.55), 'a4'=>array(595.28,841.89), 'a5'=>array(420.94,595.28),
'letter'=>array(612,792), 'legal'=>array(612,1008));
$size = $this->_getpagesize($size);
$this->DefPageSize = $size;
$this->CurPageSize = $size;
// Page orientation
$orientation = strtolower($orientation);
if($orientation=='p' || $orientation=='portrait')
{
$this->DefOrientation = 'P';
$this->w = $size[0];
$this->h = $size[1];
}
elseif($orientation=='l' || $orientation=='landscape')
{
$this->DefOrientation = 'L';
$this->w = $size[1];
$this->h = $size[0];
}
else
$this->Error('Incorrect orientation: '.$orientation);
$this->CurOrientation = $this->DefOrientation;
$this->wPt = $this->w*$this->k;
$this->hPt = $this->h*$this->k;
// Page rotation
$this->CurRotation = 0;
// Page margins (1 cm)
$margin = 28.35/$this->k;
$this->SetMargins($margin,$margin);
// Interior cell margin (1 mm)
$this->cMargin = $margin/10;
// Line width (0.2 mm)
$this->LineWidth = .567/$this->k;
// Automatic page break
$this->SetAutoPageBreak(true,2*$margin);
// Default display mode
$this->SetDisplayMode('default');
// Enable compression
$this->SetCompression(true);
// Set default PDF version number
$this->PDFVersion = '1.3';
}
// the rest of the class.....}
答案 0 :(得分：0)
试试这个
$this->Cell(30,10, $this->headerLeft);
您不需要$来访问headerLeft属性
同样适用于headerRight属性。您可以像这样访问
$this->headerRight
this->Cell(30,10, $this->headerRight);