如何使用PHP5类创建单例类?
当前回答
这是在数据库类上创建单例的例子
设计模式 1)单
class Database{
public static $instance;
public static function getInstance(){
if(!isset(Database::$instance)){
Database::$instance=new Database();
return Database::$instance;
}
}
$db=Database::getInstance();
$db2=Database::getInstance();
$db3=Database::getInstance();
var_dump($db);
var_dump($db2);
var_dump($db3);
那么输出是
object(Database)[1]
object(Database)[1]
object(Database)[1]
只使用单个实例,不要创建3个实例
其他回答
支持多对象,每类一行:
这个方法将在你想要的任何类上强制单例,你所要做的就是向你想要创建单例的类中添加一个方法,这个方法会为你做这件事。
这也将对象存储在“SingleTonBase”类中,因此您可以通过递归SingleTonBase对象来调试您在系统中使用的所有对象。
创建一个名为SingletonBase.php的文件,并将其包含在脚本的根目录中!
代码是
abstract class SingletonBase
{
private static $storage = array();
public static function Singleton($class)
{
if(in_array($class,self::$storage))
{
return self::$storage[$class];
}
return self::$storage[$class] = new $class();
}
public static function storage()
{
return self::$storage;
}
}
然后,对于任何你想要创建单例的类,只需添加这个小的单方法。
public static function Singleton()
{
return SingletonBase::Singleton(get_class());
}
这里有一个小例子:
include 'libraries/SingletonBase.resource.php';
class Database
{
//Add that singleton function.
public static function Singleton()
{
return SingletonBase::Singleton(get_class());
}
public function run()
{
echo 'running...';
}
}
$Database = Database::Singleton();
$Database->run();
你可以在任何类中添加这个单例函数,每个类只创建一个实例。
注意:你应该始终将__construct设为private以消除new Class()的使用;实例化。
您实际上不需要使用单例模式,因为它被认为是反模式。基本上,有很多理由根本不实现这种模式。首先阅读:PHP单例类的最佳实践。
如果你仍然认为你需要使用单例模式,那么我们可以写一个类,允许我们通过扩展我们的SingletonClassVendor抽象类来获得单例功能。
这就是我解决这个问题的方法。
<?php
namespace wl;
/**
* @author DevWL
* @dosc allows only one instance for each extending class.
* it acts a litle bit as registry from the SingletonClassVendor abstract class point of view
* but it provides a valid singleton behaviour for its children classes
* Be aware, the singleton pattern is consider to be an anti-pattern
* mostly because it can be hard to debug and it comes with some limitations.
* In most cases you do not need to use singleton pattern
* so take a longer moment to think about it before you use it.
*/
abstract class SingletonClassVendor
{
/**
* holds an single instance of the child class
*
* @var array of objects
*/
protected static $instance = [];
/**
* @desc provides a single slot to hold an instance interchanble between all child classes.
* @return object
*/
public static final function getInstance(){
$class = get_called_class(); // or get_class(new static());
if(!isset(self::$instance[$class]) || !self::$instance[$class] instanceof $class){
self::$instance[$class] = new static(); // create and instance of child class which extends Singleton super class
echo "new ". $class . PHP_EOL; // remove this line after testing
return self::$instance[$class]; // remove this line after testing
}
echo "old ". $class . PHP_EOL; // remove this line after testing
return static::$instance[$class];
}
/**
* Make constructor abstract to force protected implementation of the __constructor() method, so that nobody can call directly "new Class()".
*/
abstract protected function __construct();
/**
* Make clone magic method private, so nobody can clone instance.
*/
private function __clone() {}
/**
* Make sleep magic method private, so nobody can serialize instance.
*/
private function __sleep() {}
/**
* Make wakeup magic method private, so nobody can unserialize instance.
*/
private function __wakeup() {}
}
使用的例子:
/**
* EXAMPLE
*/
/**
* @example 1 - Database class by extending SingletonClassVendor abstract class becomes fully functional singleton
* __constructor must be set to protected becaouse:
* 1 to allow instansiation from parent class
* 2 to prevent direct instanciation of object with "new" keword.
* 3 to meet requierments of SingletonClassVendor abstract class
*/
class Database extends SingletonClassVendor
{
public $type = "SomeClass";
protected function __construct(){
echo "DDDDDDDDD". PHP_EOL; // remove this line after testing
}
}
/**
* @example 2 - Config ...
*/
class Config extends SingletonClassVendor
{
public $name = "Config";
protected function __construct(){
echo "CCCCCCCCCC" . PHP_EOL; // remove this line after testing
}
}
只是为了证明它能像预期的那样工作:
/**
* TESTING
*/
$bd1 = Database::getInstance(); // new
$bd2 = Database::getInstance(); // old
$bd3 = Config::getInstance(); // new
$bd4 = Config::getInstance(); // old
$bd5 = Config::getInstance(); // old
$bd6 = Database::getInstance(); // old
$bd7 = Database::getInstance(); // old
$bd8 = Config::getInstance(); // old
echo PHP_EOL."COMPARE ALL DATABASE INSTANCES".PHP_EOL;
var_dump($bd1);
echo '$bd1 === $bd2' . ($bd1 === $bd2)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
echo '$bd2 === $bd6' . ($bd2 === $bd6)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
echo '$bd6 === $bd7' . ($bd6 === $bd7)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
echo PHP_EOL;
echo PHP_EOL."COMPARE ALL CONFIG INSTANCES". PHP_EOL;
var_dump($bd3);
echo '$bd3 === $bd4' . ($bd3 === $bd4)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
echo '$bd4 === $bd5' . ($bd4 === $bd5)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
echo '$bd5 === $bd8' . ($bd5 === $bd8)? ' TRUE' . PHP_EOL: ' FALSE' . PHP_EOL; // TRUE
你可能应该添加一个私有的__clone()方法来禁止克隆实例。
private function __clone() {}
如果您不包含此方法,则可能出现以下情况
$inst1=UserFactory::Instance(); // to stick with the example provided above
$inst2=clone $inst1;
现在$inst1 !== $inst2 -它们不再是同一个实例了。
数据库类,检查是否有任何现有的数据库实例,它将返回先前的实例。
class Database {
public static $instance;
public static function getInstance(){
if(!isset(Database::$instance) ) {
Database::$instance = new Database();
}
return Database::$instance;
}
private function __cunstruct() {
/* private and cant create multiple objects */
}
public function getQuery(){
return "Test Query Data";
}
}
$dbObj = Database::getInstance();
$dbObj2 = Database::getInstance();
var_dump($dbObj);
var_dump($dbObj2);
/*
After execution you will get following output:
object(Database)[1]
object(Database)[1]
*/
Ref http://www.phptechi.com/php-singleton-design-patterns-example.html
不幸的是,当有多个子类时,Inwdr的答案就失效了。
下面是一个正确的可继承单例基类。
class Singleton
{
private static $instances = array();
protected function __construct() {}
protected function __clone() {}
public function __wakeup()
{
throw new Exception("Cannot unserialize singleton");
}
public static function getInstance()
{
$cls = get_called_class(); // late-static-bound class name
if (!isset(self::$instances[$cls])) {
self::$instances[$cls] = new static;
}
return self::$instances[$cls];
}
}
测试代码:
class Foo extends Singleton {}
class Bar extends Singleton {}
echo get_class(Foo::getInstance()) . "\n";
echo get_class(Bar::getInstance()) . "\n";
推荐文章
- 在PHP5中创建单例设计模式
- 什么时候我们应该使用观察者和可观察对象?
- 阻止人们入侵基于php的Flash游戏高分表的最佳方法是什么
- PHP子字符串提取。获取第一个'/'之前的字符串或整个字符串
- __construct函数的作用是什么?
- PHP中的异步shell执行器
- Laravel 5 -如何访问在视图存储上传的图像?
- 为什么在PHP中使用sprintf函数?
- “质量分配”在Laravel中是什么意思?
- 在逗号上爆炸字符串,并修剪每个值的潜在空格
- PHP与MySQL 8.0+错误:服务器请求身份验证方法未知的客户端
- laravel5“LIKE”对等物(雄辩的)
- 在函数中使用默认实参
- 转换php数组到Javascript
- PHP PDO:字符集,集名称?