如何初始化类中的PDO连接，以便该类中的其他方法可以访问该连接 - How to initialize a PDO connection inside a class so that other methods within that class can access that connection

How to initialize a PDO connection inside a class so that other methods within that class can access that connection

我试图在一个类中使用PDO连接，但我似乎无法正确使用。

class core{
    public $dbh;
    public function __construct(){
       try {
        $dbh = new PDO('mysql:host=localhost;dbname=sales;charset=utf8', 'root', '0150000048785', array(PDO::ATTR_EMULATE_PREPARES => false, PDO::  ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
        } catch (PDOException $e){
            echo $e->getMessage();
        }
    }

类"core"中的另一个方法;

public function varify_pwd(){
                    $varify = $this->dbh->prepare("SELECT * FROM users WHERE uid = ?");
                    self::bindParams($varify, array($_SESSION['uid']), $dbh);
                    $row = $varify->fetch();                    
                    if (password_verify($pwd, $row['pwd'])){ 
                        return true;
                        exit;
                    } else {
                        return false;
                        exit;   
                    }
    }
}

我如何使变量$dbh可用于其他方法?

class core{
public $dbh;
public function __construct(){
   try {
    //see here:
    $this->dbh = new PDO('mysql:host=localhost;dbname=sales;charset=utf8', 'root', 'password', array(PDO::ATTR_EMULATE_PREPARES => false, PDO::  ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
    } catch (PDOException $e){
        echo $e->getMessage();
    }
}