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What is a Controller?

A Controller is simply a class file. that is named in a way that can be associated with a URI. Example :
itechtuto.com/Gmax_Admin/home

here home is the controller class of that url. In the above example, CodeIgniter would attempt to find a controller named Home.php and load it.

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

create a simple controller file Home.php and put the following code in it:

File name : Home.php

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Home extends CI_Controller {

function __construct()
{

parent::__construct();

}
public function index()
{
//$this->load->view('login');
// echo 'Hello World!';
redirect('admin/Login');

}
}

Then save the file to your application/controllers/ directory.
Note : The file must be called 'Home.php', with a capital 'H'.

Note : Class names must start with an uppercase letter.

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:

http://itechtuto.com/Home/index/

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

<?php
class Home extends CI_Controller {

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

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

How to get controller name & Method name

public function index()
{
$controller = $this->router->fetch_class();
$method = $this->router->fetch_method();
print_r($controller);
print_r($method);
exit;
}

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:
http://itechtuto.com/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;
}
}

Remapping Method Calls :-

Second segment of URI determines which method is being called. If you want to override it you can use _remap() method. method named _remap which allows you to overwrite the behavior of calling your controller methods over URI.
If you have mentioned _remap() method in your controllers, it will always get called even if URI is different. It overrides the URI.

Now think about the following factors:

You want to hide your original method name from the URI

You want to named second segment of your URI as you like

You want to make a control over your controller methods so that you can decide which method should be called using URI

CodeIgniter permits you to override its default routing behavior through the use of the _remap() function. As you already knew the second segment of the URI typically determines with function is in the controller get called and it will be passed as a parameter to the _remap() function. So to hide the real method name in the URL you can use _remap() and you can define your own set of routing rules.

If your controller contains a function named _remap(), it will always get called regardless of what your URI contains. It overrides the normal behavior. in which the URI determines which function is called, allowing you to define your own function routing rules. For example: your URL is http://itechtuto.com/post/index and you do not want to call index for this then you can use _remap() to map new function view instead of index like this.

class Blog extends CI_Controller
{
public function _remap($method)
{
if ($method == 'index')
{
$this->postList();
}
else
{
show_404();
}
}

public index()
{
echo "hello index default method";
}

public function postList() {
echo "show postlist";
}

}

public function _remap($methodName)
{
if ($methodName === 'a_method')
{
$this->method();
}
else
{
$this->defaultMethod();
}
}

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.

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();
}

class Blog extends Controller
{
function _remap( $method )
{
// $method contains the second segment of your URI
switch( $method )
{
case 'about-me':
$this->about_me();
break;

case 'successful':
$this->display_successful_message();
break;

default:
$this->page_not_found();
break;
}
}

function index()
{
// ---
}

function about_me()
{
// ---
}

function display_successful_message()
{
// ---
}

function page_not_found ()
{
// ---
}

function secure_method()
{
// ---
}

function Blog()
{
parent::Controller();
}
}

Processing Output :

CodeIgniter has an output class that takes care of sending your final rendered data to the web browser automatically. 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. It is also responsible for caching your web pages, if you use that feature.

Note : If your controller contains a method named _output(), it will always be called by the output class instead of echoing the finalized data directly. The first parameter of the method will contain the finalized output.

Note : This class is initialized automatically by the system so there is no need to do it manually.

Here is an example:

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

Please note that your _output() method will receive the data in its finalized state. Benchmark and memory usage data will be rendered, cache files written (if you have caching enabled), and headers will be sent (if you use that feature) before it is handed off to the _output() method. To have your controller’s output cached properly, its _output() method can use:

if ($this->output->cache_expiration > 0)
{
$this->output->_write_cache($output);
}
If you are using this feature the page execution timer and memory usage stats might not be perfectly accurate since they will not take into account any further processing you do. For an alternate way to control output before any of the final processing is done,

Itechtuto