如何关闭从扩展的类

Question

连接我有一个单独的数据库连接类 - db.php中（通过在google找到）：

<?php 
/* 
* Mysql database class - only one connection alowed 
*/ 
class db { 
    private $_connection; 
    private static $_instance; //The single instance 
    private $_host = "localhost"; 
    private $_username = "user_name"; 
    private $_password = "password"; 
    private $_database = "database"; 

    /* 
    Get an instance of the Database 
    @return Instance 
    */ 
    public static function getInstance() { 
     if(!self::$_instance) { // If no instance then make one 
      self::$_instance = new self(); 
     } 
     return self::$_instance; 
    } 

    // Constructor 
    private function __construct() { 
     $this->_connection = new mysqli($this->_host, $this->_username, 
      $this->_password, $this->_database); 

     // Error handling 
     if(mysqli_connect_error()) { 
      trigger_error("Failed to conencto to MySQL: " . mysql_connect_error(), 
       E_USER_ERROR); 
     } 

    // Magic method clone is empty to prevent duplication of connection 
    private function __clone() { } 

    // Get mysqli connection 
    public function getConnection() { 
     return $this->_connection; 
    } 

    public function closeConnection(){ 
     $this->_connection->close(); 
    } 
} 
?> 

测试连接，如果我在ext.php延长该数据库类像这样：

<?php 
class ext extends db { 
private $conn; 
function __construct(){ 
$this->connect(); 
if(isset($this->conn)){ 
     echo 'Connection is established<br />'; 
    } 
$this->closeConn(); 
} 
public function connect(){ 
    $this->conn = parent::getInstance()->getConnection(); 
} 
public function closeConn(){ 
    parent::closeConnection(); 
} 
} 
?> 

，并在我的index.php页面：

<?php 
spl_autoload_register(function ($class) { 
    include '../classes/' . $class . '.php'; 
}); 
$test = new ext(); 
?> 

现在我的输出如下：

Connection is established 
Fatal error: Call to a member function close() on a non-object in (line number) of db.php 

我的问题是如何关闭扩展类（ext.php）中的连接？

Answer 1

解决办法是这样的：

• 首先，在ext类创建父db类的private实例变量，像这样：

  class ext extends db { 
      ... 
      private $parentInstance; 
      ... 
  } 
  

• 然后使用这个实例变量$parentInstance创建并关闭您的连接，如下所示：

  class ext extends db { 
      private $conn; 
      private $parentInstance; 
      function __construct(){ 
       $this->connect(); 
       if(isset($this->conn)){ 
        echo 'Connection is established<br />'; 
       } 
       $this->closeConn(); 
      } 
      public function connect(){ 
       $this->parentInstance = parent::getInstance(); 
       $this->conn = $this->parentInstance->getConnection(); 
      } 
      public function closeConn(){ 
       $this->parentInstance->closeConnection(); 
      } 
  } 
  

---

旁注：有一个在db类中的一个小的语法错误也是如此。构造函数方法的右括号缺失。