What is Singleton ?
i am not a good person to define things, but any way , when you feel you need only one instance from a class then you need a singleton!
Did computer scientists waste their time to instantiate only one object?
absolutely no , it is a very useful solution , some time having multiple copies of objects can lead to chaos , resource looking , resource over used , …. etc
When it is needed?
Most of the common usage is to handle global setting like database connections , registry settings , who is online now ? , .etc
here is an example to implement singleton while connecting to MYSQL connection
<?php
//ConnectionConf.php
class ConnectionConf
{
public $Username;
public $Password;
public $ServerAddress;
public $Database;
}
?>
<?php
require_once 'ConnectionConf.php';
class Connection
{
/**
* Varaible to hold the unique instance
* @var Connection
*/
private static $UniqueInstance;
/**
* Connetion User name
* @var string
*/
private $_strUsername;
/**
* Connection Password
* @var string
*/
private $_strPassword;
/**
* Connection Address
* @var string
*/
private $_strServerAddress;
/**
* Database Name
* @var string
*/
private $_strDatabase;
/**
* Last Error happend
* @var string
*/
private $_strLastError;
/**
* mysql link identfier
* @var mysql resource
*/
private $_resConnectionResource;
/**
* Class constructor , it is private ,
* so no way you can create it using new Connection
* @param $ConnectionConf ConnectionConf
* @return void
*/
private function __construct($ConnectionConf)
{
$this->_strUsername=$ConnectionConf->Username;
$this->_strPassword=$ConnectionConf->Password;
$this->_strServerAddress=$ConnectionConf->ServerAddress;
$this->_strDatabase=$ConnectionConf->Database;
$this->StartConnection();
}
/**
* @param $ConnectionConf ConnectionConf
* @return Connection
*/
public static function GetInstance ($ConnectionConf=null)
{
if (Connection::$UniqueInstance==null)
{
if ($ConnectionConf==null)
throw new Exception("Connection Configuration Can't be null at first time");
Connection::$UniqueInstance = new Connection($ConnectionConf);
return Connection::$UniqueInstance ;
}
return Connection::$UniqueInstance ;
}
/////////////////////////////// Sets and Gets Start///////////////////////////////////
public function GetUsername ()
{
return $this->_strUsername;
}
public function GetPassword ()
{
return $this->_strPassword;
}
public function GetServerAddress ()
{
return $this->_strServerAddress;
}
public function GetDatabaseName()
{
return $this->_strDatabase;
}
public function GetConnectionResource ()
{
return $this->_resConnectionResource;
}
public function GetLastError ()
{
return $this->_strLastError;
}
////////////////////////////Sets And Gets End/////////////////////////////////////////////////////
/**
*
* @return bool
*/
public function StartConnection ()
{
try{
$this->_resConnectionResource=mysql_connect($this->_strServerAddress,$this->_strUsername,
$this >_strPassword);
mysql_select_db($this->_strDatabase);
}
catch(Exception $e){
$this->_strLastError=$e->getMessage();
return 0 ;
}
return 1;
}
public function CloseConnection ()
{
try{
mysql_close($this->_resConnectionResource);
}
catch (Exception $e)
{
$this->_strLastError=$e->getMessage();
return 0 ;
}
return 1;
}
public function RestartConnection ()
{
$this->CloseConnection();
$this->StartConnection();
}
}
$Config = new ConnectionConf();
$Config->Username= "root";
$Config->Password= "";
$Config->ServerAddress= "localhost";
$Config->Database= "road";
//First instance
$Connection = Connection::GetInstance($Config);
var_dump($Connection);
//will return the same instance declared before
$Connection1 = Connection::GetInstance();
var_dump($Connection1);
?>
here are the files
http://www.4shared.com/file/9d_RHQ0I/ConnectionConf.html
http://www.4shared.com/file/DoOt0KUh/singleton.html
