[英]extends a singleton class in PHP
<?php
class LoveBase
{
protected static $_instance = NULL;
protected function __construct() {}
public static function app()
{
if(self::$_instance == NULL) {
self::$_instance = new self();
}
return self::$_instance;
}
public function get()
{
return 'LoveBase';
}
}
class Love extends LoveBase
{
public static function app()
{
if(self::$_instance == NULL) {
self::$_instance = new self();
}
return self::$_instance;
}
public function get()
{
return 'Love';
}
}
// Print "LoveLove" in this case(first case)
echo Love::app()->get();
echo LoveBase::app()->get();
// Print "LoveBaseLoveBase" in this case(second case)
// echo LoveBase::app()->get();
// echo Love::app()->get();
为什么两种不同的方法得出相同的结果?
比较这两种情况,该方法在类首次实例化时将起作用。
(对不起,我的英语不好,希望你能说出来)
您定义了两个静态函数,它们都使用相同的静态变量($ _instance)-基类的静态成员也可以通过子类访问(只要它不是私有的)。 请记住,静态的东西(方法和变量)是继承的,而不是克隆的。
解决方案:将成员变量设为私有,并为每个类创建一个。
class LoveBase
{
private static $_instance = NULL;
// ...
class Love extends LoveBase
{
private static $_instance = NULL;
// ...
// Print "LoveLove" in this case(first case)
//Set self::$_instance to Love object id
echo Love::app()->get();
//Static property $_instance is now already set, so LoveBase::app() won't create new self(), it will just return created and saved Love object
echo LoveBase::app()->get();
// Print "LoveBaseLoveBase" in this case(second case)
// Here is the same case, but static property $_instance filled with new self() in LoveBase class
// echo LoveBase::app()->get();
// echo Love::app()->get();
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