In this tutorial, you are going to learn the following topics.

  • Routing – routing is responsible for responding to URL requests. Routing matches the URL to the pre-defined routes. If no route match is found then, CodeIgniter throws a page not found an exception.
  • Controllers – routes are linked to controllers. Controllers glue the models and views together. The request for data/business logic from the model and return the results in the presentation of the view. Once a URL has been matched to a route, it is forwarded to a controller's public function. This function interacts with the data source, business logic and returns the view that displays the results.
  • Views – views are responsible for presentation. A view is usually a combination of HTML, CSS, and JavaScript. This is the part is responsible for displaying the web page to the user. Typically, the data displayed is usually retrieved from the database or any other available data sources.

In this tutorial, you will learn-

How to create a new CodeIgniter project

We will use Composer to create a new project. I will be using the PHP built-in server, so it's not necessary to have extra software such as Apache. In this tutorial, we are using the Windows operating system. Therefore, we have created a Sites folder on drive C. You can use any directory that is suitable for you.

Open the command line/terminal and run the following command

cd C:\Sites

We will now create a CodeIgniter project using Composer. Run the following command

composer create-project CodeIgniter/framework ci-app

HERE,

  • The above command creates a new CodeIgniter project version 3 using the latest stable release i.e., 3.1.9 into a directory ci-app.

When the above command has completed running, you should be able to results similar to the following in the terminal

Run the following command to browse to the newly created project directory ci-app

cd ci-app

Let's now start the PHP built-in web server

 php -S localhost:3000 

HERE,

  • The above command starts the built-in PHP server running on port 3000.

Open the web browser and browse the following URL

http://localhost:3000/

You will get the following page

If you can see the above page then congratulations, you have successfully installed CodeIgniter.

As you can read from the above web page, the page displayed above is rendered by the view located in application/views/welcome_message.php and the responsible controller is located in application/controllers/Welcome.php

CodeIgniter Routing

For now, our application has only a single URL which is the home page. In this section, we will customize the home section. We will create some new URLs that will respond to the different requests.

Let's start with the home page route

Open the routes file as indicated by the path below

application/config/routes.php 
You should be able to see the following content
$route['default_controller'] = 'welcome';
$route['404_override'] = '';
$route['translate_uri_dashes'] = FALSE;

HERE,

  • $route['default_controller'] = 'welcome'; defines the default controller that responds to the URI requests
  • $route['404_override'] = ''; this route allows you to define a custom route for 404 errors. A 404 error occurs when a page is not found. CodeIgniter has a default handler for the error but you can define your own if you so wish.
  • $route['translate_uri_dashes'] = FALSE; this option allows you to translate dashes to underscores. We will talk about this option when we look at how routes work in CodeIgniter.

Let's now look at the controller method responsible for displaying the home page that we saw when we opened the URL http://localhost:3000/ in the web browser

Open the following file

application/controllers/Welcome.php

You should be able to see the following code

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

class Welcome extends CI_Controller {

	public function index()
	{
		$this->load->view('welcome_message');
	}
}

HERE,

  • Defined ('BASEPATH') OR exit('No direct script access allowed'); protects against directly accessing the controller class without passing through the index.php file. Remember, in MVC paradigm all requests have a single entry point, and for CodeIgniter, its index.php. This code blocks all requests that do not come through index.php
  • class Welcome extends CI_Controller {…} defines a class Welcome that extends the parent class CI_Controller
  • public function index() defines a public function that is called by default when you open the homepage
  • $this->load->view('welcome_message'); this line loads the view welcome_message. The file welcome_message is located in the directory application/views/welcome_message.php

So far, we have only explored what comes out of the box with CodeIgniter, let's now try to make some changes. We will create our home page and replace the default page

Create a new file in application/views/home.php

Add the following code to home.php

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <title>Hello CodeIgniter!</title>
        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css">
        <script defer src="https://use.fontawesome.com/releases/v5.3.1/js/all.js"></script>
    </head>
    <body>
        <section class="section">
            <div class="container">
                <h1 class="title">
                    CodeIgniter Hello World
                </h1>
            </div>
        </section>
    </body>
</html>

HERE,

The above HTML code loads Burma SSS framework and font from CDN network create a very basic HTML document. It applies very simple CSS rule from Burma CSS framework.

Open the following URL in your browser

http://localhost:3000/

You should be able to see the following

Great, we have just successfully modified the home page. Moving on, let's define our route. Let's assume our application also needs to be able to show the about us page.

Create a Route

Open the routes file application/config.routes.php

Add the following route

$route['about-us'] = 'welcome/about_us';

HERE,

  • When a visitor visits the URL /about-us, we are instructing CodeIgniter to look for a controller Welcome and execute the method about_us.

Create a Controller

Let's now define the controller method about us

Open application/controllers/Welcome.php

Add the following method

        public function about_us(){
            $this->load->view('about_us');
        }

HERE,

  • The above code defines a function about_us and loads a view about_us.

Create a View

Let's now create the view that we just referenced in the above section

Create a new file about_us.php in application/views/about_us.php

Add the following code

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <title>About CodeIgniter!</title>
        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css">
        <script defer src="https://use.fontawesome.com/releases/v5.3.1/js/all.js"></script>
    </head>
    <body>
        <section class="section">
            <div class="container">
                <h1 class="title">
                    About us yap...                
                </h1>
            </div>
        </section>
    </body>
</html>

We are good to go, open the following URL in your web browser

http://localhost:3000/index.php/about-us

You will see the following page

If you are able to see the above page then congratulations, you have successfully created a simple application in CodeIgniter.

Summary

In this tutorial, we covered three (3) major components that make up a CodeIgniter application. We looked at routes and how to define them, controllers and how to create methods that respond to route requests and created simple views that are returned to the users when they request for a resource.

 

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