如何使用PHP5类创建单例类?
当前回答
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。
其他回答
我同意第一个答案,但我也会将类声明为final,这样它就不能被扩展,因为扩展单例违背了单例模式。此外,实例变量应该是私有的,这样就不能直接访问它。还要将__clone方法设为私有,这样就不能克隆单例对象。
下面是一些示例代码。
/**
* Singleton class
*
*/
final class UserFactory
{
private static $_instance = null;
/**
* Private constructor
*
*/
private function __construct() {}
/**
* Private clone method
*
*/
private function __clone() {}
/**
* Call this method to get singleton
*
* @return UserFactory
*/
public static function getInstance()
{
if (self::$_instance === null) {
self::$_instance = new UserFactory();
}
return self::$_instance;
}
}
示例使用
$user_factory = UserFactory::getInstance();
这阻止你做什么(这将违反单例模式..
你不能这么做!
$user_factory = UserFactory::$_instance;
class SecondUserFactory extends UserFactory { }
制作单例模式的真实和现代方法是:
<?php
/**
* Singleton Pattern.
*
* Modern implementation.
*/
class Singleton
{
/**
* Call this method to get singleton
*/
public static function instance()
{
static $instance = false;
if( $instance === false )
{
// Late static binding (PHP 5.3+)
$instance = new static();
}
return $instance;
}
/**
* Make constructor private, so nobody can call "new Class".
*/
private 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() {}
}
现在你可以用它。
<?php
/**
* Database.
*
* Inherited from Singleton, so it's now got singleton behavior.
*/
class Database extends Singleton {
protected $label;
/**
* Example of that singleton is working correctly.
*/
public function setLabel($label)
{
$this->label = $label;
}
public function getLabel()
{
return $this->label;
}
}
// create first instance
$database = Database::instance();
$database->setLabel('Abraham');
echo $database->getLabel() . PHP_EOL;
// now try to create other instance as well
$other_db = Database::instance();
echo $other_db->getLabel() . PHP_EOL; // Abraham
$other_db->setLabel('Priler');
echo $database->getLabel() . PHP_EOL; // Priler
echo $other_db->getLabel() . PHP_EOL; // Priler
正如你所看到的,这种实现更加灵活。
下面是我的例子,它提供了调用as $var = new Singleton()的能力,并创建了3个变量来测试它是否创建了新对象:
class Singleton{
private static $data;
function __construct(){
if ($this::$data == null){
$this->makeSingleton();
}
echo "<br/>".$this::$data;
}
private function makeSingleton(){
$this::$data = rand(0, 100);
}
public function change($new_val){
$this::$data = $new_val;
}
public function printme(){
echo "<br/>".$this::$data;
}
}
$a = new Singleton();
$b = new Singleton();
$c = new Singleton();
$a->change(-2);
$a->printme();
$b->printme();
$d = new Singleton();
$d->printme();
class Database{
//variable to hold db connection
private $db;
//note we used static variable,beacuse an instance cannot be used to refer this
public static $instance;
//note constructor is private so that classcannot be instantiated
private function __construct(){
//code connect to database
}
//to prevent loop hole in PHP so that the class cannot be cloned
private function __clone() {}
//used static function so that, this can be called from other classes
public static function getInstance(){
if( !(self::$instance instanceof self) ){
self::$instance = new self();
}
return self::$instance;
}
public function query($sql){
//code to run the query
}
}
Access the method getInstance using
$db = Singleton::getInstance();
$db->query();
protected static $_instance;
public static function getInstance()
{
if(is_null(self::$_instance))
{
self::$_instance = new self();
}
return self::$_instance;
}
这段代码可以应用于任何类,而无需关心类名。