PHP CodeIgniter框架的工作原理研究

<?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;
		}

		// couldnt 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;
	}