php OOP 错误：在第 7 行的 c:blah/bla/../\engine\admin\cms.class.php 中调用 null 上的成员函数 query()

Posted 2023-02-24

【中文标题】php OOP 错误：在第 7 行的 c:blah/bla/../\\engine\\admin\\cms.class.php 中调用 null 上的成员函数 query()

【英文标题】：php OOP error: Call to a member function query() on null in c:blah/bla/../\engine\admin\cms.class.php on line 7php OOP 错误：在第 7 行的 c:blah/bla/../\engine\admin\cms.class.php 中调用 null 上的成员函数 query()

【发布时间】：2016-07-24 22:19:03

【问题描述】：

尝试在另一个类中打开扩展类时发生错误..

mydb.php

 <?php 
class mydb
    public $conn;
    function __construct()
        $this->conn=new mysqli("localhost","root","","akshaya");
        $this->_conn=$this->conn;
       if(!$this->conn)
           echo "mysql connection error";
       else
           return $this->conn;
       
    


?>

login.class.php

 <?php
include_once __DIR__.'\..\mydb.php';
class vishnuADMIN extends mydb 
    public function login($uname,$password)
        $uname=$this->conn->real_escape_string($uname);
        $password=$this->conn->real_escape_string($password);

    $password="s4l8".sha1($password);
    $q="select * from user where uname='$uname' and password='$password'";
    $res=$this->conn->query($q);
       if(mysqli_num_rows($res))
//           (!isset($_SESSION))? session_start() :"";
           $_SESSION["user"]=$uname;
           return true;
       else
           return false;
       
    
    public function register($uname,$password)
        $password="s4l8".sha1($password);
       echo $q="INSERT INTO user(uname,password) VALUES ('$uname','$password')";
        $res=$this->conn->query($q);
        if($res)
            (!isset($_SESSION))?session_start():"";
            $_SESSION["user"]=$uname;
            return true;
        else
            return false;
        

    
      public function logincheck()
//        (!isset($_SESSION))?session_start():"";
        if(isset($_SESSION["user"]))
            return true;
        else
             return false;
        
    
    public function logout()
//        (!isset($_SESSION))?session_start():"";
        session_unset();
    


//$obj=new vishnuADMIN();
//if($obj->logincheck())
//    echo "hai";
//

cms.class.php

 <?php 
class paginator_vishnukumar extends mydb 
    private $_limit,$_page,$_query,$_total,$_conn;
    public function __construct( $query ) 
    $this->_query = $query;
    $rs= $this->conn->query( $this->_query );
    $this->_total = $rs->num_rows;  
    public function getData(  $page = 1,$limit = 10 ) 
    $this->_limit   = $limit;
    $this->_page    = $page;
 /*
        some blah blah codes...

        */
    
    public function createLinks( $links, $list_class ) 
    if ( $this->_limit == 'all' ) 
        return '';
    /*
        some blah blah codes...

        */
    

    return $html;


?>

admin.php

 <?php 
require 'engine/vishnuHTML.class.php';
require 'engine/admin/login.class.php';
$html=new vishnuHTML();
 (!isset($_SESSION))?session_start():"";
$html->head();
$html->navigation();
$log=new vishnuADMIN();
/* vishnuADMIN::login("vishnu","vishnukumar"); */
if(isset($_POST['submit']))
    if($log->login($_POST['uname'],$_POST['password']))
logedin();
    else
        echo "invalid";
    


if($log->logincheck())
 logedin();
else
    loginform();


?>



<?php



$html->footer();
function loginform()
?>
<div class="row">

    <div class="login columns">
    <div class="four column">
<form method="post" action="">
<label>User name</label>
<input type="text" name="uname"><br>
<label>Password</label>
<input type="password" name="password"><br>
<input type="submit" value="go" name="submit"><br>
</form>
</div>
</div>
</div>
<?php



function logedin()
        require 'engine/admin/cms.class.php';
    $limit      = ( isset( $_GET['limit'] ) ) ? $_GET['limit'] : 25;
    $page       = ( isset( $_GET['page'] ) ) ? $_GET['page'] : 1;
    $links      = ( isset( $_GET['links'] ) ) ? $_GET['links'] : 7;
    $query      = "SELECT * FROM pages";
    $Paginator  = new paginator_vishnukumar( $query );
    $results    = $Paginator->getData( $page, $limit );

?>

请检查此代码

抛出错误： 致命错误：在第 7 行的 C:..\engine\admin\cms.class.php 中的 null 上调用成员函数 query()

login.class.php 和 cms.class.php 中的扩展类 mydb 如何在多个页面/类中使用连接变量类..

【问题讨论】：

显然$this->conn在调用$this->conn->query时没有定义

我认为 $this->conn 应该是 $this->_conn

“只有在创建对象时才会调用构造函数！”，简单地扩展类不会调用构造函数。

【参考方案1】：

您需要在 cms.class.php 中调用 parent::__construct();

<?php 
class paginator_vishnukumar extends mydb 
    private $_limit,$_page,$_query,$_total,$_conn;

    public function __construct( $query ) 

        parent::__construct(); // <-- will initiate the connection

        $this->_query = $query;
        $rs= $this->conn->query( $this->_query );
        // ....