Research on the working principle of PHP CodeIgniter framework, codeigniter framework_PHP tutorial

Research on the working principle of PHP CodeIgniter framework, codeigniter framework

CodeIgniter (hereinafter referred to as CI, official website and Chinese website) is a popular PHP framework, small but powerful, simple and light It also has good scalability and is quite popular in China. On the other hand, CI has not kept pace with the times and does not support some features after PHP5.3, making it relatively more suitable for older projects. Even so, CI is still an excellent framework, and it has a smaller core, elegant source code, and is suitable for learning.

CI is easy to use and can easily develop web applications. Let’s first take a look at the CI workflow diagram (the content here is quoted from http://codeigniter.org.cn/user_guide/overview/appflow.html)

,
1.index.php serves as the front-end controller to initialize the basic resources required to run CodeIgniter.
2.Router checks the HTTP request to determine who should handle the request.
3. If the cache file exists, it will bypass the usual system execution sequence and be sent directly to the browser.
4. Security. HTTP requests and any user-submitted data will be filtered before the Application Controller is loaded.
5. The Controller loads models, core libraries, helper functions, and any other resources needed to handle specific requests.
6. The final view renders the content sent to the web browser. If caching is turned on, the view is cached first so it will be available for future requests.

The above gives a general process. So when you see the page rendered in the browser, how exactly does the program work internally?
The following is a list of the main files loaded by the CI framework in order of execution, and a brief introduction to their functions:

01. index.php
Define the usage environment (ENVIRONMENT), framework path (system_path, BASEPATH), application directory (application_folder), application path (APPPATH), etc., and load (require) the CI core file
02. BASEPATH/core/CodeIgniter.php (ps. Actually BASEPATH contains the final file separator '/', the additional '/' is added here for clearer display)
The system initialization file, the core part of the entire framework, loads a series of base classes here and executes this request
03. BASEPATH/core/Common.php
The common file contains a series of basic and public functions for global use, such as load_class(), get_config(), etc.
04. BASEPATH/core/Benchmark
This is a benchmark test class that by default marks the execution points of each stage of the application to obtain its execution time. Also allows you to define monitoring points yourself.
05. BASEPATH/core/Hooks.php
CI_Hooks is a hook class, which is the core of the framework expansion. It can insert hook points at various stages allowed by the program and execute your customized classes, functions, etc.
06. BASEPATH/core/Config.php
Configuration file management class, load, read or set configuration
07. BASEPATH/core/URI.php, BASEPATH/core/Router.php
The URI class helps you parse the requested URI and provides a set of functions to split the URI for use by the Router class
08. BASEPATH/core/Router.php
The routing class distributes user requests to the specified processing function (usually an action in a Controller instance) through the requested URI and the user-configured route (APPPATH/config/routes.php). function)
09. BASEPATH/core/Output.php, BASEPATH/core/Input.php
The input class handles the input parameters of the request and provides a safe way to obtain them. The output class sends out the final execution results, and is also responsible for the caching function
10. BASEPATH/core/Controller.php
Controller base class, using singleton mode to provide instances to the outside world, the heart of the entire application. It is a Super Object. Classes loaded within the application can become member variables of the controller. This is very important and will be discussed later.
11. APPPATH/controllers/$RTR->fetch_directory().$RTR->fetch_class().'.php'
Through the routing function, get the controller name and instantiate the real controller class (subclass)
12. BASEPATH/core/Loader.php
CI_Loader is used to load various class libraries, models, views, databases, files, etc. in the application, and set them as member variables of the controller
13. call_user_func_array calls the processing function
Through routing, get the action function name, call the Controller->action() function, and process the application logic. The actual business processing logic is written in the action function
14. $OUT->_display() outputs the content

The above is the most basic processing flow of the entire application. The following selects the core content code and explains it to enhance the understanding of CI:

<&#63;php
//*BASEPATH/system/core/Common.php
	//引导文件中Benchmark,Hooks,Config等都是通过这个函数进行加载的
	function &load_class($class, $directory = 'libraries', $prefix = 'CI_')
	{
		//记录加载过的类
		static $_classes = array();

		// 已经加载过，直接读取并返回
		if (isset($_classes[$class]))
		{
			return $_classes[$class];
		}

		$name = FALSE;

		// 在指定目录寻找要加载的类
		foreach (array(APPPATH, BASEPATH) as $path)
		{
			if (file_exists($path.$directory.'/'.$class.'.php'))
			{
				$name = $prefix.$class;

				if (class_exists($name) === FALSE)
				{
					require($path.$directory.'/'.$class.'.php');
				}

				break;
			}
		}

		// 没有找到
		if ($name === FALSE)
		{
			exit('Unable to locate the specified class: '.$class.'.php');
		}

		// 追踪记录下刚才加载的类，is_loaded()函数在下面
		is_loaded($class);

		$_classes[$class] = new $name();
		return $_classes[$class];
	}
	// 记录已经加载过的类。函数返回所有加载过的类
	function &is_loaded($class = '')
	{
		static $_is_loaded = array();

		if ($class != '')
		{
			$_is_loaded[strtolower($class)] = $class;
		}

		return $_is_loaded;
	}

//*BASEPATH/system/core/Controller.php
class CI_Controller {

	private static $instance;

	public function __construct()
	{
		self::$instance =& $this;
		
		//将所有在引导文件中(CodeIgniter.php)初始化的类对象(即刚才4,5,6,7,8,9等步骤)，
		//注册成为控制器类的成员变量，就使得这个控制器成为一个超级对象(super object)
		foreach (is_loaded() as $var => $class)
		{
			$this->$var =& load_class($class);
		}
<span style="white-space:pre">		</span>//加载Loader对象，再利用Loader对象对程序内一系列资源进行加载<span style="white-space:pre">	</span>
		$this->load =& load_class('Loader', 'core');

		$this->load->initialize();
		
		log_message('debug', "Controller Class Initialized");
	}

	//这个函数对外提供了控制器的单一实例
	public static function &get_instance()
	{
		return self::$instance;
	}
}


//*BASEPATH/system/core/CodeIgniter.php
	// Load the base controller class
	require BASEPATH.'core/Controller.php';

	//通过这个全局函数就得到了控制器的实例，得到了这个超级对象，
	//意味着在程序其他地方调用这个函数，就能得到整个框架的控制权
	function &get_instance()
	{
		return CI_Controller::get_instance();
	}

	// 加载对应的控制器类
	// 注意：Router类会自动使用 router->_validate_request() 验证控制器路径
	if ( ! file_exists(APPPATH.'controllers/'.$RTR->fetch_directory().$RTR->fetch_class().'.php'))
	{
		show_error('Unable to load your default controller. Please make sure the controller specified in your Routes.php file is valid.');
	}

	include(APPPATH.'controllers/'.$RTR->fetch_directory().$RTR->fetch_class().'.php');

	$class = $RTR->fetch_class(); //Controller class name
	$method = $RTR->fetch_method(); //action name

	//.....

	// 调用请求的函数
	// uri中除了class/function之外的段也会被传递给调用的函数
	call_user_func_array(array(&$CI, $method), array_slice($URI->rsegments, 2));

	//输出最终的内容到浏览器
	if ($EXT->_call_hook('display_override') === FALSE)
	{
		$OUT->_display();
	}
	

//*BASEPATH/system/core/Loader.php
	//看一个Loader类加载model的例子。这里只列出了部分代码
	public function model($model, $name = '', $db_conn = FALSE)
	{
		$CI =& get_instance();
		if (isset($CI->$name))
		{
			show_error('The model name you are loading is the name of a resource that is already being used: '.$name);
		}

		$model = strtolower($model);

		//依次根据model类的path进行匹配，如果找到了就加载
		foreach ($this->_ci_model_paths as $mod_path)
		{
			if ( ! file_exists($mod_path.'models/'.$path.$model.'.php'))
			{
				continue;
			}

			if ($db_conn !== FALSE AND ! class_exists('CI_DB'))
			{
				if ($db_conn === TRUE)
				{
					$db_conn = '';
				}

				$CI->load->database($db_conn, FALSE, TRUE);
			}

			if ( ! class_exists('CI_Model'))
			{
				load_class('Model', 'core');
			}

			require_once($mod_path.'models/'.$path.$model.'.php');

			$model = ucfirst($model);

			//这里依然将model对象注册成控制器类的成员变量。Loader在加载其他资源的时候也会这么做
			$CI->$name = new $model();

			$this->_ci_models[] = $name;
			return;
		}

		// couldn't find the model
		show_error('Unable to locate the model you have specified: '.$model);
	}

//*BASEPATH/system/core/Model.php
	//__get()是一个魔术方法，当读取一个未定义的变量的值时就会被调用
	//如下是Model基类对__get()函数的一个实现，使得在Model类内，可以像直接在控制器类内一样(例如$this->var的方式)去读取它的变量
	function __get($key)
	{
		$CI =& get_instance();
		return $CI->$key;
	}