PHP 实现类的自动加载

使用 spl_autoload_register() 函数实现类的自动加载

一个文件中，往往需要使用多个别的类。这种情况下，一般是必须先在文件顶部使用 require/require_once或 include_include_once 进行加载，才能实例函数。

使用 spl_auto_register() 实现自加载的执行过程输出：

Trying to loadClass1 via ClassAutoloader::loader()
Class1::__construct
Trying to loadClass2 via Class
Autoloader::loader() Class2::__construct

spl_autoload_register - Register given function as __autoload() implementation

Description

bool spl_autoload_register([ callable $autoload_function [, bool $throw = true [, bool $prepend = false ]]])


Register a function with the spl provided __autoload queue. If the queue is not yet activated it will be activated.

If your code has an existing __autoload() function then this function must be explicitly registered on the __autoload queue. This is because spl_autoload_register()

will efectively replace the engine cache for the __autoload() function by either spl_autoload() or spl_autoload_call().

If there must be multiple autoload functions, spl_autoload_register() allows for this. It effectively creates a queue of autoload functions, and runs through each of 
them in the order they are defined. By contrast, __autoload() may only be defined once.

目录结构：

• modernphp/ClasssAutoloader.php
• modernphp/Class1.php
• mordernphp/Class2.php

ClassAutokloader.php

class ClassAutoloader 
{
    
    public function __construct() {
        spl_autoload_register(array($this, 'loader'));
    }
    
    public function loader($className) {
        
        echo "Trying to load" , $className, ' via ', __METHOD__, "()\n";
        echo "<br/>";
        include $className . '.php';
    }
    
}

$autoloader = new ClassAutoloader();

$obj = new Class1();
$obj = new Class2();

Class1.php

<?php

class Class1
{
    
    public function __construct()
    {
        
        echo __METHOD__;
        echo "<br/>";
    }
}

Class2.php

<?php

class Class1
{
    
    public function __construct()
    {
        
        echo __METHOD__;
        echo "<br/>";
    }
}