Problem Creating a Class

[berliner_kindl]

I am trying to convert one of my older scripts into OOP with a class but I have a question: how do I reference a variable between methods within the same class? I tried using $this->variable with no luck.

Here's the code:

<?php

class DisplayCat {

  // Insures that the value of $cat is valid

  public function CheckCatValue($cat)
    {
       if (($cat == "") || ($cat == "0")) 
         {
           echo "category was left blank";
         }
       elseif (is_numeric($cat) == false) 
         {
           echo "category must be a numeric value";
         }
        else 
         {
           $this->DisplayProducts($cat);	  
         }
    }

    // Loops through the category and displays produts

	public function DisplayProducts($cat)
	  {
            $getProducts = mysql_query("SELECT * FROM products WHERE prod_cat = $cat LIMIT $this->offset,$this->rowsperpage") or die(mysql_error());
            $num_rows = mysql_num_rows($getProducts);

            while($row = mysql_fetch_array( $getProducts )) 
		  {
		  $prod_id = $row["prod_id"];
		  $prod_title = $row["prod_title"];
		  $prod_pprice = $row["prod_pprice"];
		  $prod_gprice = $row["prod_gprice"];
		  $prod_thumb = $row["prod_thumb"];

		  for ($n = 1; $n <=4; $n++) 
		    {
		    }

            echo "
		<div class=\"catbody_block\">
	          <div class=\"catbody_img\">
		    <a href=\"product.php?product=$prod_id\"><img src=\"$prod_thumb\" border=\"0\" alt=\"$prod_id\" /></a>
		  </div>
		  <div class=\"catbody_data\">
		    &nbsp;$prod_id | $prod_pprice <br /> &nbsp;$prod_title
		    <br />&nbsp;<a href=\"product.php?product=$prod_id\"><img src=\"images/_info.gif\" border=\"0\" alt=\"info\"/></a><a href=\"addtocart.php?product=$prod_id\"><img src=\"images/_buy.gif\" border=\"0\" /></a>
		  </div>
		</div>";
	    }
	  }

  // Creates pagination values

  public function CreatePagination($cat,$sql,$conn) 
    {
      $sql = "SELECT COUNT(*) FROM products WHERE prod_cat = $cat";  
      $result = mysql_query($sql, $conn) or trigger_error("SQL", E_USER_ERROR);  
      $r = mysql_fetch_row($result);  
      $numrows = $r[0];  

		if ($numrows == 0) 
		  {
		    echo "Numrows = 0";
		  } 
        else 
		  {
		    $rowsperpage = 12;  
			$totalpages = ceil($numrows / $rowsperpage); 

        if (isset($_GET['currentpage']) && is_numeric($_GET['currentpage'])) 
	  {  
             $currentpage = (int) $_GET['currentpage'];  
          } 
        else 
	  {  
	    $currentpage = 1;  
	  } 
			
        if ($currentpage > $totalpages) 
	  {  
	    $currentpage = $totalpages;  
	  }  
				 
	if ($currentpage < 1) 
	  {  
	    $currentpage = 1;  
	  }  
				 
        $offset = ($currentpage - 1) * $rowsperpage;  
     }
  }

   // Displays pagination footer

    public function DisplayPagination($cat)
	{
          echo "<div class=\"catbody_pagination\">More:&nbsp;";
		
	  if ($this->currentpage > 1) 
	    {  
              echo "<a href='{$_SERVER['PHP_SELF']}?$this->currentpage=1&cat=$cat'><<&nbsp;</a> ";  

	      $prevpage = $this->currentpage - 1;  
        
	    } 

	  $range = 12;  
      
	  for ($x = ($this->currentpage - $range); $x < (($this->currentpage + $range)  + 1); $x++) 
	    {  
		  if (($x > 0) && ($x <= $this->totalpages)) 
		    {  
			  if ($x == $this->currentpage) 
			    {  
			      echo "$x";  
				} 
				else
				{  
                  echo " <a href='{$_SERVER['PHP_SELF']}?$this->currentpage=$x&cat=$cat'>$x</a> ";  
				}
			} 
		}
   
	  if ($this->currentpage != $this->totalpages) 
	    {  
		  $nextpage = $this->currentpage + 1;   
		  //  echo " <a href='{$_SERVER['PHP_SELF']}?currentpage=$nextpage&cat=$cat'>></a> ";  
		  echo " <a href='{$_SERVER['PHP_SELF']}?$this->currentpage=$this->totalpages&cat=$cat'>&nbsp;>></a>";  
		}

	  echo "&nbsp;&nbsp&nbsp;&nbsp&nbsp;&nbsp;</div>";
	}
}


?>

<?php
  include ("classes/displaycat.php");
  $cat = mysql_real_escape_string($_GET['cat']);

  $DisplayCat = new DisplayCat;

    $CheckCatValue = $DisplayCat->CheckCatValue($cat);
    $CreatePagination = $DisplayCat->CreatePagination($cat);
    $DisplayPagination = $DisplayCat->DisplayPagination($cat);
		
?>

I get this error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1

and assume it has to do with not properly passing the values of LIMIT $offset,$rowsperpage - how do I do that?

[Cups]

    public function DisplayProducts($cat)
      {
            $getProducts = mysql_query("SELECT * FROM products 
WHERE prod_cat = $cat 
LIMIT $this->offset,
$this->rowsperpage"
) or die(mysql_error());
            $num_rows = mysql_num_rows($getProducts); 

Take $this->offset - where is $this->offset set? and where is it stored so that those methods can get hold of it?

You could have a class "property" and declare it at the top of your class like so:

class yourclass {

public $offset = 10 ;

public function DisplayProducts(){

return "offset is now " . $this->offset ;

}

public function setOffset( $n ){

$this->offset = $n ;

}

} 

Classes generally have properties upon which methods operate.

$d = new yourclass ;
$d->setOffset( 15 );  // optional, let default ride if you prefer
echo $d->DisplayProducts(); 

It is usually seen as a bad sign if your classes echo anything, they should return values, or data only - maybe have a final class which dresses up the output as html as opposed to a pdf, or a csv file
EDIT
Your sql is wrong because your class cannot assemble the sql statement, echo the sql statement as you work away - that will give you a better clue as to where you are going wrong.

[berliner_kindl]

$offset is defined by the CreatePagination function like this:

$offset = ($currentpage - 1) * $rowsperpage;

So how do I pass that value from the CreatePagination function to the DisplayProducts function?

I am going to remove all of the html from the DisplayProducts loop and keep them separate, sorry... I just included here while trying to wireframe and get this working.

If I declare the variables like this:

var $foffset = $this->offset;
var $frowsperpage = $this->rowsperpage;

in the class, will that work?

[Cups]

$offset is defined by the CreatePagination function like this:

$offset = ($currentpage - 1) * $rowsperpage;

So how do I pass that value from the CreatePagination function to the DisplayProducts function?

$this->offset = ($currentpage - 1) * $rowsperpage;

I am going to remove all of the html from the DisplayProducts loop and keep them separate, sorry... I just included here while trying to wireframe and get this working.

If I declare the variables like this:

var $foffset = $this->offset;
var $frowsperpage = $this->rowsperpage;

in the class, will that work?

No.

If you are using PHP5 you'd declare it using one of PPP (public,private,protected) not var whats more the declaration can only be a scalar value, or nothing at all.

so

public $offset = 10;
OR
public $offset ;

offset is now available for each method to access (read) or change (write) if they want to simply by adding $this-> before it like this $this->offset.

You'd better read up on classes, the syntax is not difficult, but if you don't put some learning time in, you'll be forever asking how they work.

Classes get super complex super quick and before you know - all kinds of rules kick in and you lose track of what is over-writing what.

The man is the best starting place to learn the syntax and roles and responsibilities. http://fr.php.net/manual/en/language.oop5.php

[oddz]

class DisplayCat {

    protected $category;
    protected $db;

    protected $offset;
    protected $currentPage;
    protected $pages;
    
    public function __construct($category,$db) {
    
        $this->category = $category;
        $this->db = $db;
        
        $this->_init();
    
    }
    
    protected function _init() {
    
        $this->displayProducts();
    
    }
    
    public function getOffset() {
    
        if(is_null($this->offset)) {
            $this->_createPagination();
        }
        
        return $this->offset;
    
    }
    
    public function getCurrentPage() {
    
        if(is_null($this->currentPage)) {
            $this->_createPagination();
        }
        
        return $this->currentPage;
    
    }
    
    public function getPages() {
    
        if(is_null($this->pages)) {
            $this->_createPagination();
        }
        
        return $this->pages;
    
    }
    
    protected function _createPagination() {
    
        // code to calculate offset, current page and pages
        
        $this->offset = $offset;
        $this->pages = $pages;
        $this->currentPage = $currentPage
    
    }
    
    public function displayProducts() {
    
        $offset = $this->getOffset();
        
        $this->displayPagination();
    
    }
    
    public function displayPagination() {
    
        $offset = $this->getOffset();
        $currentPage = $this->getCurrentPage();
        $pages = $this->getPages();    
    
    }

} 

[berliner_kindl]

what does the underscore do?

$this->_createPagination();

I assume it signifies private vars like C++?

[Ernie1]

what does the underscore do?

nothing special

[berliner_kindl]

Cool. What about the _init function name, is there any significance to that? I cannot find anything in the manual or on google about that, but it seems like an odd name.

[Ernie1]

It is the place where you can perform some application-level initialization tasks.
It's just a naming convention.

[oddz]

Using a underscore nicely distinguishes methods that are part of the public interface from those that are not. However, I don't follow this convention with properties because they are always either private or protected.