Controllers

Controllers are the heart of your application, as they determine how HTTP requests should be handled.

Page Contents

• Controllers
  • What is a Controller?
  • Let’s try it: Hello World!
  • Methods
  • Passing URI Segments to your methods
  • Defining a Default Controller
  • Remapping Method Calls
  • Processing Output
  • Private methods
  • Organizing Your Controllers into Sub-directories
  • Class Constructors
  • Reserved method names
  • That’s it!

What is a Controller?

A Controller is simply a class file that is named in a way that can be associated with a URI.

Consider this URI:

example.com/index.php/blog/

In the above example, CodeIgniter would attempt to find a controller named Blog.php and load it.

When a controller’s name matches the first segment of a URI, it will be loaded.

Let’s try it: Hello World!

Let’s create a simple controller so you can see it in action. Using your text editor, create a file called Blog.php, and put the following code in it:

<?php
class Blog extends CI_Controller {

        public function index()
        {
                echo 'Hello World!';
        }
}

Then save the file to your application/controllers/ directory.

Now visit the your site using a URL similar to this:

example.com/index.php/blog/

If you did it right, you should see:

This is valid:

<?php
class Blog extends CI_Controller {

}

This is not valid:

<?php
class blog extends CI_Controller {

}

Also, always make sure your controller extends the parent controller class so that it can inherit all its methods.

Methods

In the above example the method name is index(). The “index” method is always loaded by default if the second segment of the URI is empty. Another way to show your “Hello World” message would be this:

example.com/index.php/blog/index/

The second segment of the URI determines which method in the controller gets called.

Let’s try it. Add a new method to your controller:

<?php
class Blog extends CI_Controller {

        public function index()
        {
                echo 'Hello World!';
        }

        public function comments()
        {
                echo 'Look at this!';
        }
}

Now load the following URL to see the comment method:

example.com/index.php/blog/comments/

You should see your new message.

Passing URI Segments to your methods

If your URI contains more than two segments they will be passed to your method as parameters.

For example, let’s say you have a URI like this:

example.com/index.php/products/shoes/sandals/123

Your method will be passed URI segments 3 and 4 (“sandals” and “123”):

<?php
class Products extends CI_Controller {

        public function shoes($sandals, $id)
        {
                echo $sandals;
                echo $id;
        }
}

Defining a Default Controller

CodeIgniter can be told to load a default controller when a URI is not present, as will be the case when only your site root URL is requested. To specify a default controller, open your application/config/routes.php file and set this variable:

$route['default_controller'] = 'blog';

Where ‘blog’ is the name of the controller class you want used. If you now load your main index.php file without specifying any URI segments you’ll see your “Hello World” message by default.

For more information, please refer to the “Reserved Routes” section of the URI Routing documentation.

Remapping Method Calls

As noted above, the second segment of the URI typically determines which method in the controller gets called. CodeIgniter permits you to override this behavior through the use of the _remap() method:

public function _remap()
{
        // Some code here...
}

The overridden method call (typically the second segment of the URI) will be passed as a parameter to the _remap() method:

public function _remap($method)
{
        if ($method === 'some_method')
        {
                $this->$method();
        }
        else
        {
                $this->default_method();
        }
}

Any extra segments after the method name are passed into _remap() as an optional second parameter. This array can be used in combination with PHP’s call_user_func_array() to emulate CodeIgniter’s default behavior.

Example:

public function _remap($method, $params = array())
{
        $method = 'process_'.$method;
        if (method_exists($this, $method))
        {
                return call_user_func_array(array($this, $method), $params);
        }
        show_404();
}

Processing Output

CodeIgniter has an output class that takes care of sending your final rendered data to the web browser automatically. More information on this can be found in the Views and Output Class pages. In some cases, however, you might want to post-process the finalized data in some way and send it to the browser yourself. CodeIgniter permits you to add a method named _output() to your controller that will receive the finalized output data.

Here is an example:

public function _output($output)
{
        echo $output;
}

if ($this->output->cache_expiration > 0)
{
        $this->output->_write_cache($output);
}

Private methods

In some cases you may want certain methods hidden from public access. In order to achieve this, simply declare the method as being private or protected and it will not be served via a URL request. For example, if you were to have a method like this:

private function _utility()
{
        // some code
}

Trying to access it via the URL, like this, will not work:

example.com/index.php/blog/_utility/

Organizing Your Controllers into Sub-directories

If you are building a large application you might want to hierarchically organize or structure your controllers into sub-directories. CodeIgniter permits you to do this.

Simply create sub-directories under the main application/controllers/ one and place your controller classes within them.

application/controllers/products/Shoes.php

example.com/index.php/products/shoes/show/123

Each of your sub-directories may contain a default controller which will be called if the URL contains only the sub-directory. Simply put a controller in there that matches the name of your ‘default_controller’ as specified in your application/config/routes.php file.

CodeIgniter also permits you to remap your URIs using its URI Routing feature.

Class Constructors

If you intend to use a constructor in any of your Controllers, you MUST place the following line of code in it:

parent::__construct();

The reason this line is necessary is because your local constructor will be overriding the one in the parent controller class so we need to manually call it.

Example:

<?php
class Blog extends CI_Controller {

        public function __construct()
        {
                parent::__construct();
                // Your own constructor code
        }
}

Constructors are useful if you need to set some default values, or run a default process when your class is instantiated. Constructors can’t return a value, but they can do some default work.

Reserved method names

Since your controller classes will extend the main application controller you must be careful not to name your methods identically to the ones used by that class, otherwise your local functions will override them. See Reserved Names for a full list.

That’s it!

That, in a nutshell, is all there is to know about controllers.