[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::$_instance;
}
public function get()
{
return 'Love';
}
}
// Print "LoveLove" in this case(first case)
echo Love::app()->get();
echo LoveBase::app()->get();
// Print "LoveBaseLoveBase" in this case(second case)
// echo LoveBase::app()->get();
// echo Love::app()->get();
為什么兩種不同的方法得出相同的結果?
比較這兩種情況,該方法在類首次實例化時將起作用。
(對不起,我的英語不好,希望你能說出來)
您定義了兩個靜態函數,它們都使用相同的靜態變量($ _instance)-基類的靜態成員也可以通過子類訪問(只要它不是私有的)。 請記住,靜態的東西(方法和變量)是繼承的,而不是克隆的。
解決方案:將成員變量設為私有,並為每個類創建一個。
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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