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diff --git a/user_guide_src/source/general/creating_libraries.rst b/user_guide_src/source/general/creating_libraries.rst new file mode 100644 index 000000000..d322f56eb --- /dev/null +++ b/user_guide_src/source/general/creating_libraries.rst @@ -0,0 +1,187 @@ +################## +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, CodeIgniter 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. 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 CodeIgniter 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 { public function some_function() { } } /* End of file Someclass.php */ + +Using Your Class +================ + +From within any of your :doc:`Controller <controllers>` 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. CodeIgniter +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 as an +array via the second parameter and it will be passed to your class +constructor:: + + $params = array('type' => 'large', 'color' => 'red'); $this->load->library('Someclass', $params); + +If you use this feature you must set up your class constructor to expect +data:: + + <?php if ( ! defined('BASEPATH')) exit('No direct script access allowed'); class Someclass { public function __construct($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 CodeIgniter Resources within Your Library +=================================================== + +To access CodeIgniter's native resources within your library use the +get_instance() function. This function returns the CodeIgniter super +object. + +Normally from within your controller functions you will call any of the +available CodeIgniter 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 CodeIgniter's classes +from within your own custom classes you can do so as follows: + +First, assign the CodeIgniter 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 CodeIgniter 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 CodeIgniter 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 this 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 nearly identical to replacing a class with a +couple exceptions: + +- The class declaration must extend the parent class. +- Your new class name and filename must be prefixed with MY\_ (this + item is configurable. See below.). + +For example, to extend the native Email class you'll create a file named +application/libraries/MY_Email.php, and declare your class with:: + + class MY_Email extends CI_Email { } + +Note: If you need to use a constructor in your class make sure you +extend the parent constructor:: + + class MY_Email extends CI_Email { public function __construct() { parent::__construct(); } } + +Loading Your Sub-class +---------------------- + +To load your sub-class you'll use the standard syntax normally used. DO +NOT include your prefix. For example, to load the example above, which +extends the Email class, you will use:: + + $this->load->library('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(); + +Setting Your Own Prefix +----------------------- + +To set your own sub-class prefix, open your +application/config/config.php file and look for this item:: + + $config['subclass_prefix'] = 'MY_'; + +Please note that all native CodeIgniter libraries are prefixed with CI\_ +so DO NOT use that as your prefix. |