Creating Libraries
When we use the term "Libraries" we are normally referring to the classes that are located in the libraries directory and described in the Class Reference of this user guide. In this case, however, we will instead describe how you can create your own libraries within your application/libraries directory in order to maintain separation between your local resources and the global framework resources.
As an added bonus, Code Igniter permits your libraries to extend native classes if you simply need to add some functionality to an existing library. Or you can even replace native libraries just by placing identically named versions in your application/libraries folder.
In summary:
- You can create entirely new libraries.
- You can extend native libraries.
- You can replace native libraries.
The page below explains these three concepts in detail.
Note: The Database classes can not be extended or replaced with your own classes, nor can the main Controller class. All other classes are able to be replaced/extended.
Storage
Your library classes should be placed within your application/libraries folder, as this is where Code Igniter will look for them when they are initialized.
Naming Conventions
- File names must be capitalized. For example: Myclass.php
- Class declarations must be capitalized. For example: class Myclass
- Class names and file names must match.
The Class File
Classes should have this basic prototype (Note: We are using the name Someclass purely as an example):
<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
class Someclass {
function some_function()
{
}
}
?>
Using Your Class
From within any of your Controller functions you can initialize your class using the standard:
$this->load->library('someclass');
Where someclass is the file name, without the ".php" file extension. You can submit the file name capitalized or lower case. Code Igniter doesn't care.
Once loaded you can access your class using the lower case version:
$this->someclass->some_function(); // Object instances will always be lower case
Passing Parameters When Initializing Your Class
In the library loading function you can dynamically pass data via the second parameter and it will be passed to your class constructor:
$params = array('type' => 'large', 'color' => 'red');
$this->load->library('Someclass', $params);
If you use this feature you must set up your class constructor to expect data:
<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
class Someclass {
function Someclass($params)
{
// Do something with $params
}
}
?>
You can also pass parameters stored in a config file. Simply create a config file named identically to the class file name and store it in your application/config/ folder. Note that if you dynamically pass parameters as described above, the config file option will not be available.
Utilizing Code Igniter Resources within Your Library
To access Code Igniter's native resources within your library use the get_instance() function. This function returns the Code Igniter super object.
Normally from within your controller functions you will call any of the available Code Igniter functions using the $this construct:
$this->load->helper('url');
$this->load->library('session');
$this->config->item('base_url');
etc.
$this, however, only works directly 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.
Replacing Native Libraries with Your Versions
Simply by naming your class files identically to a native library will cause Code Igniter to use it instead of the native one. To use this feature you must name the file and the class declaration exactly the same as the native library. For example, to replace the native Email library you'll create a file named application/libraries/Email.php, and declare your class with:
class CI_Email {
}
Note that most native classes are prefixed with CI_.
To load your library you'll see the standard loading function:
$this->load->library('email');
Note: At thit time the Database classes can not be replaced with your own versions.
Extending Native Libraries
If all you need to do is add some functionality to an existing library - perhaps add a function or two - then it's overkill to replace the entire library with your version. In this case it's better to simply extend the class.
Extending a class is identical to replacing a class with one exception: The class declaration must extend the parent class and your new class must be prefixed with MY_. For example, to extend the native Email class you'll create a file named application/libraries/Email.php, and declare your class with:
class MY_Email extends CI_Email {
}
class MY_Email extends CI_Email {
function My_Email()
{
parent::CI_Email();
}
}
Important: To tell Code Igniter to load your sub-class you MUST include my_ in the loading function:
$this->load->library('my_email');
Once loaded you will use the class variable as you normally would for the class you are extending. In the case of
the email class all calls will use:
$this->email->some_function();