Parameter visibility problem

[richie]

I'm just trying to learn OOP, but experiencing teething problems so far.

Please explain what is wrong with the following code.

I expected the output to be something like:

/images/2126151275

but instead I get:

/2126151275

Why doesn't testEcho() see the $uploadDir parameter, even though it was declared public?

<?

class R_resizeImage
{
public $finalFileName;
public $uploadDir;
public $nameOfFile;

    public function __construct()
    {
            $this->finalFileName = mt_rand();
            $this->nameOfFile = $this->uploadDir . '/' . $this->finalFileName;
    }

   public function testEcho()
  {
     return($this->nameOfFile);
  }

}

$c = new ResizeImage();
$c->uploadDir = '/images';
echo $c->testEcho();

?>

[nrg_alpha]

I would take note of this forum's new name 🙂
This sounds like a Coding forum post as this does not pertain to upgrade or release issues..

and as the sample code.. I'm just starting out in OOP myself..

Just out of curiosity.. what is the purpose of a blank construct (when you instantiate your object)? Looks like you could have simply used a good old fashioned function instead?

As for your problem, could you not include the last slash in the $uploadDir variable as such?

$c->uploadDir = '/images/';

and not bother with that last slash in the assigning of the variable nameOfFile?

$this->nameOfFile = $this->uploadDir . $this->finalFileName;

Cheers,

NRG

*Edit: This also caught my eye.. should this instantiating line:

$c = new ResizeImage();

be this instead?

$c = new R_resizeImage();

[bretticus]

I expected the output to be something like:

/images/2126151275

but instead I get:

/2126151275

That's because you set nameOfFile in your constructor. As you may remember, your constructor code is called when you instantiate a new object from the class.

$c = new R_resizeImage();

So even though you changed the uploadDir property after you instantiated the object, nameOfFile has already been set in the constructor with an empty uploadDir property (too late.)

What you can do is set nameOfFile in your testEcho method.

public function testEcho()
{
	$this->nameOfFile = $this->uploadDir . '/' . $this->finalFileName;
	return($this->nameOfFile);
}

Or leave testEcho alone and set uploadDir in the constructor:

class R_resizeImage
{
	public $finalFileName;
	public $uploadDir;
	public $nameOfFile;

public function __construct($uploadDir)
{
	$this->uploadDir = $uploadDir;
	$this->finalFileName = mt_rand();
	$this->nameOfFile = $this->uploadDir . '/' . $this->finalFileName;
}

public function testEcho()
{
	return($this->nameOfFile);
}
}

$c = new R_resizeImage('/images');
echo $c->testEcho();

[nrg_alpha]

I suppose this answers the contructor with no variables being passed..(my blank constructor question). I suppose if you want to set up some native variables with set behaviors (found inside the constructor), you don't necessarily need to set up the constructor to pass anything in (unless you want to pass something to the inside for aiding in variable setup)?

The __construct() has always confused me somewhat.. but this explaination clears things very much!

Cheers,

NRG

[richie]

"That's because you set nameOfFile in your constructor. As you may remember, your constructor code is called when you instantiate a new object from the class."

That explains it then.

I didn't realize that the constructor gets called before any external parameters are set.

Thanks for your clear explanation.

[Weedpacket]

richie wrote:

I didn't realize that the constructor gets called before any external parameters are set.

The constructor is called when the object is constructed; which is

$c = new ResizeImage(); //<-- Here