PHP Design Patterns: Page Controller

The Page Controller design pattern is a common architectural approach used in web-based systems. It organizes the flow of control by dedicating a specific controller to handle the logic for an individual page or request. This approach helps isolate responsibilities, making the codebase easier to maintain and evolve.

What is the Page Controller?

In the Page Controller pattern, each page (or a group of pages with similar behavior) has its own controller, responsible for:

1. Handling the request: Processing data sent from the client.
2. Executing the page-specific logic: Validating input, interacting with models, or performing computations.
3. Rendering a response: Passing processed data to a view (template) and returning the final response to the client.

Advantages of the Pattern

1. Simple flow: Each page is mapped to its own dedicated controller.
2. Separation of concerns: Each controller handles only its own logic.
3. Maintainability: Changes to one page affect only its associated controller.
4. Scalability: Adding new pages is straightforward and doesn’t disrupt existing functionality.

Basic Structure

A typical implementation involves the following components:

• Controllers: PHP files containing logic for specific pages.
• Routes: A routing mechanism to map URLs to controllers.
• Views: Templates used to render the user interface.

Flow

1. The client sends a request to a specific URL.
2. The routing system identifies the appropriate controller for the request.
3. The controller executes the required logic and delegates the response rendering to a view.
4. The view generates the final output and returns it to the client.

Implementation Example

File Structure

/htdocs
    /src
        /Controllers
            HomeController.php
            AboutController.php
        /Services
            ViewRenderer.php
        /Views
            home.html.php
            about.html.php
    /public
        index.php
    /routes.php
    composer.json

Autoloader

{
    "autoload": {
        "psr-4": {
            "App\": "htdocs/"
        }
    }
}

composer dump-autoload

Template

Template for the homepage and about.html.php.

    <title>= htmlspecialchars($title) ?></title>


    <h1 id="htmlspecialchars-title-gt">= htmlspecialchars($title) ?></h1>
    <p>= htmlspecialchars($content) ?></p>

ViewRenderer

namespace App\Services;

class ViewRenderer {

    public function render(string $view, array $data = []): void {
        extract($data); // Turns array keys into variables
        include __DIR__ . "/../../Views/{$view}.html.php";
    }
}

HomeController

Handles the homepage logic.

namespace App\Controllers;

use App\Services\ViewRenderer;

class HomeController {

    public function __construct(private ViewRenderer $viewRenderer)
    {
    }

    public function handleRequest(): void {
        $data = [
            'title' => 'Welcome to the Site',
            'content' => 'Homepage content.',
        ];

        $this->viewRenderer->render('home', $data);
    }
}

AboutController

Handles the "About Us" page logic.

namespace App\Controllers;

use App\Services\ViewRenderer;

class AboutController
{

    public function __construct(private ViewRenderer $viewRenderer)
    {
    }

    public function handleRequest(): void {
        $data = [
            'title' => 'About Us',
            'content' => 'Information about the company.',
        ];

        $this->viewRenderer->render('about', $data);
    }
}

routes.php

Defines route mappings to controllers.

use App\Controllers\HomeController;
use App\Controllers\AboutController;

// Define the routes in an associative array
return [
    '/' => HomeController::class,
    '/about' => AboutController::class,
];

index.php

The application’s entry point.

/htdocs
    /src
        /Controllers
            HomeController.php
            AboutController.php
        /Services
            ViewRenderer.php
        /Views
            home.html.php
            about.html.php
    /public
        index.php
    /routes.php
    composer.json

Pros and Cons

Advantages

• Organization: Controllers are modular, each handling a specific page.
• Reusability: Views can be reused across different controllers.
• Debugging: Errors are easier to trace since each page has its own dedicated controller.

Disadvantages

• Increased number of controllers: Large projects can lead to a proliferation of controllers, requiring better organization.
• Code duplication: Common logic across controllers may be repeated. This can be mitigated by using a base controller class.

When to Use the Page Controller Pattern?

• Simple systems: Best for small to medium-sized web applications where each page has specific logic.
• Modular projects: When you want to isolate logic for easier maintenance.
• Without frameworks: Ideal for PHP projects without robust frameworks (like Laravel or Symfony).

For more complex projects, where there is significant logic reuse or multiple entry points, patterns like Front Controller or full MVC architecture may be more suitable.

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