問題描述

我有這個類用于使用 php/mysqli 連接到 mysql 數據庫:

class AuthDB {私人 $_db;公共函數 __construct() {$this->_db = new mysqli(DB_SERVER, DB_USER, DB_PASS, DB_NAME)or die("連接數據庫有問題.錯誤:".mysqli_error());}公共函數 __destruct() {$this->_db->close();未設置($this->_db)；}}

現在，我有列表用戶的任何頁面:

require_once 'classes/AuthDB.class.php';session_start();$this->_db = new AuthDB();//這條線的錯誤$query = "SELECT Id, user_salt, password, is_active, is_verified FROM Users where email = ?";$stmt = $this->_db->prepare($query);//綁定參數$stmt->bind_param("s", $email);//執行語句如果 ($stmt->execute()) {//綁定結果列$stmt->bind_result($id, $salt, $pass, $active, $ver);//獲取第一行結果$stmt->fetch();回聲 $id;}

現在，我看到這個錯誤:

致命錯誤:第 6 行中不在對象上下文中時使用 $this

如何修復這個錯誤?！

就像錯誤所說的那樣，您不能在類定義之外使用 $this.要在類定義之外使用 $_db，首先將其設為 public 而不是 private:

public $_db

然后，使用此代碼:

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

--

您必須了解 $this 的實際含義.在類定義中使用時，$this 用于引用該類的對象.因此，如果您在 AuthDB 中有一個函數 foo，并且您需要從 foo 內訪問 $_db，您將使用 $this 告訴 PHP 您想要 $_db 來自 foo 所屬的同一對象.

您可能想閱讀這個 StackOverflow 問題: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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