从另一个类n php访问变量作为对象

Question

Hello am trying to access the pdo object returned from DatabaseConnection class in Database class but its giving me difficulty am using singleton pattern .please help

class DatabaseConnection {
    protected static $_instance = NULL;
    public static $pdo;
    private function __construct() {
        try {
            $this->pdo = new PDO ( 'mysql:host=' . Configuration::getConfiguration ( 'mysql/host' ) . ';dbname=' . Configuration::getConfiguration ( 'mysql/databaseName' ), Configuration::getConfiguration ( 'mysql/user' ), Configuration::getConfiguration ( 'mysql/password' ) );
        } catch ( PDOException $e ) {
            echo 'woops !connection to the server failed.' . $e->getMessage ();
        }
    }


    public static function getConnectionInstance() {
        if (! isset ( self::$_instance )) {
            self::$_instance = new DatabaseConnection ();
        }
        return self::$_instance;
    }
}/*end od DatabaseConnection*/



class Database implements DatabaseInterface {
    public static function select($fields = array(), $table, $where = array()) 
    {
        $fields = '`' . implode ( '`,`', $fields ) . '`';
        $fix = '';
        $x = 1;
        foreach ( $where as $tableField => $value ) {
            $fix .= "`{$tableField}` = '{$value}'";
            if ($x < count ( $where )) {
                $fix .= ' AND ';
            }
            $x ++;
        }
        $sql = "SELECT {$fields} FROM `{$table}`  WHERE {$fix} ";
        if (DatabaseConnection::$pdo->prepare ( $sql )) {
            echo 'prepared';
        }
        return false;
    } 
}

Answer 1

The $pdo member should be an instance member instead of class member. Change public static $pdo to public $pdo only. Then you can access the PDO instance by

DatabaseConnection::getConnectionInstance()->pdo;