What is the purpose of "Get Instance" in Codeigniter? How would you explain this to a total beginner?
+2
A:
It's an implementation of the singleton pattern. Essentially, there is only one instance of the class in question, which is designed to be accessible globally. The get_instance method is static and so provides a way of accessing the instance from anywhere in your code.
Will Vousden
2010-05-12 13:58:16
Not noobish enough. I'm a SUPER NOOB! :)
Kevin Brown
2010-05-12 14:37:09
@Kevin: In that case I recommend you start reading about object-oriented programming (OOP) before delving into a framework that relies upon it!
Will Vousden
2010-05-12 15:09:02
Will do, Will!!
Kevin Brown
2010-05-12 15:11:39
+3
A:
Ok, so everything in CodeIgniter runs through the super-magic $this variable. This only works for classes, as $this basically defines the current class.
Your controller is a class, so $this is there, allowing you to do $this->load->model('whatever');
In models, you are also using a class. It is slightly different here, as $this only contains useful stuff as you are extending from Model. Still, $this is still valid.
When you are using a helper or a library, you need to find that "instance" or $this equivalent.
$ci =& get_instance();
…makes $ci contain the exact same stuff/code/usefulness as $this, even though you are not in a class, or not in a class that inherits it.
That's an explanation for total beginners after 2 pints, so it's either retarded or about right. ;-)
Phil Sturgeon
2010-05-12 14:35:00
2 pints, eh? Then what is the usefullness of a library/helper? Why not just use models?
Kevin Brown
2010-05-12 14:38:10
Of course seeing as everything is a PHP class you CAN put whatever you like wherever you like. Generally speaking in CodeIgniter it is broken down as "database interaction/business logic" = models, simple functions go in helpers and general classes are libraries.
Phil Sturgeon
2010-05-13 08:07:12