Creating Ancillary Classes
In some cases you may want to develop classes that exist apart from your controllers but have the ability to utilize all of Code Igniter's resources. This is easily possible as you'll see.
get_instance()
Any class that you instantiate within your controller functions can access Code Igniter's native resources simply by using the get_instance() function. This function returns the main Code Igniter object.
Normally, to call any of the available Code Igniter functions requires you to use the $this construct:
$this->load->helper('url');
$this->load->library('session');
$this->config->item('base_url');
etc.
$this, however, only works within your controllers, your models, or your views. If you would like to use Code Igniter's classes from within your own custom classes you can do so as follows:
First, assign the Code Igniter object to a variable:
$CI =& get_instance();
Once you've assigned the object to a variable, you'll use that variable instead of $this:
$CI =& get_instance();
$CI->load->helper('url');
$CI->load->library('session');
$CI->config->item('base_url');
etc.
Note: You'll notice that the above get_instance() function is being passed by reference:
$CI =& get_instance();
This is very important. Assigning by reference allows you to use the original Code Igniter object rather than creating a copy of it.