问题描述

我有这个类用于使用 php/mysqli 连接到 mysql 数据库:

class AuthDB {私人 $_db;公共函数 __construct() {$this->_db = new mysqli(DB_SERVER, DB_USER, DB_PASS, DB_NAME)or die("连接数据库有问题.错误:".mysqli_error());}公共函数 __destruct() {$this->_db->close();未设置($this->_db)；}}

现在，我有列表用户的任何页面:

require_once 'classes/AuthDB.class.php';session_start();$this->_db = new AuthDB();//这条线的错误$query = "SELECT Id, user_salt, password, is_active, is_verified FROM Users where email = ?";$stmt = $this->_db->prepare($query);//绑定参数$stmt->bind_param("s", $email);//执行语句如果 ($stmt->execute()) {//绑定结果列$stmt->bind_result($id, $salt, $pass, $active, $ver);//获取第一行结果$stmt->fetch();回声 $id;}

现在，我看到这个错误:

致命错误:第 6 行中不在对象上下文中时使用 $this

如何修复这个错误?！

就像错误所说的那样，您不能在类定义之外使用 $this.要在类定义之外使用 $_db，首先将其设为 public 而不是 private:

public $_db

然后，使用此代码:

$authDb = new AuthDb();$authDb->_db->prepare($query);//其余代码相同

--

您必须了解 $this 的实际含义.在类定义中使用时，$this 用于引用该类的对象.因此，如果您在 AuthDB 中有一个函数 foo，并且您需要从 foo 内访问 $_db，您将使用 $this 告诉 PHP 您想要 $_db 来自 foo 所属的同一对象.

您可能想阅读这个 StackOverflow 问题:PHP:self vs $this>

i have this class for connect to mysql database using php/mysqli:

class AuthDB {
    private $_db;

    public function __construct() {
        $this->_db = new mysqli(DB_SERVER, DB_USER, DB_PASS, DB_NAME)
        or die("Problem connect to db. Error: ". mysqli_error());
    }

    public function __destruct() {
        $this->_db->close();
        unset($this->_db);
    }
}

now, i have any page for list user :

require_once 'classes/AuthDB.class.php';

session_start();

$this->_db = new AuthDB(); // error For This LINE
$query = "SELECT Id, user_salt, password, is_active, is_verified FROM Users where email = ?";
$stmt = $this->_db->prepare($query);

        //bind parameters
        $stmt->bind_param("s", $email);

        //execute statements
        if ($stmt->execute()) {
            //bind result columnts
            $stmt->bind_result($id, $salt, $pass, $active, $ver);

            //fetch first row of results
            $stmt->fetch();

            echo $id;


        }

now, i see this error:

Fatal error: Using $this when not in object context in LINE 6

How to fix this error?!

Like the error says, you can't use $this outside of the class definition. To use $_db outside the class definition, first make it public instead of private:

public $_db

Then, use this code:

$authDb = new AuthDb();
$authDb->_db->prepare($query); // rest of code is the same

--

You have to understand what $this actually means. When used inside a class definition, $this is used to refer to an object of that class. So if you had a function foo inside AuthDB, and you needed to access $_db from within foo, you would use $this to tell PHP that you want the $_db from the same object that foo belongs to.

You might want to read this StackOverflow question: PHP: self vs $this

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