调用成员函数是否为null? [英] Call to a member function on null?
问题描述
我已经做了各种各样的事情来理解代码的实际错误,但是我无法弄清楚是什么原因导致了该错误.
I have done all sorts of things to understand what is actually wrong with the code, but I just couldn't figure out what was causing this error.
下面是名为Topic
的类:
class Topic {
// Init DB variables
private $db;
/*
* Constructor
*/
public function __contruct() {
$this->db = new Database();
}
/*
* Get All Topics
*/
public function getAllTopics() {
$this->db->query("SELECT topics.*, users.username,
users.avatar, categories.name
FROM topics
INNER JOIN users
ON topics.user_id = users.id
INNER JOIN categories
ON topics.category_id = categories.id
ORDER BY create_date DESC");
// Assign the results
$results = $this->db->resultset();
return $results;
}
}
当我创建类Topic
的对象时,
$topic = new Topic();
$results = $topic->getAllTopics();
总是有这样的错误:
致命错误:在 /Applications/XAMPP/xamppfiles/htdocs/forumproject/libraries/Topic.php 在第25行,即$ this-> db-> query(...)
Fatal error: Call to a member function query() on null in /Applications/XAMPP/xamppfiles/htdocs/forumproject/libraries/Topic.php on line 25 i.e. $this->db->query(...)
Database
类运行良好,因为我已经对该类进行了独立运行的测试,并且没有问题.
The Database
class is working perfectly as I have run tests independently for that class, and there is no problem with it.
这是数据库类:
<?php
/*
* Using PDO for the first time in my life.
*/
class Database {
private $host = DB_HOST;
private $user = DB_USER;
private $pass = DB_PASS;
private $dbname = DB_NAME;
private $dbh;
private $error;
private $stmt;
public function __construct() {
// Set DSN
$dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
// Set options
$options = array(
PDO::ATTR_PERSISTENT => true,
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
);
// Create a new PDO instance
try {
$this->dbh = new PDO($dsn, $this->user, $this->pass, $options);
}
// Catch the errors using exceptions handler
catch(PDOException $e){
$this->error = $e->getMessage();
}
}
public function query($query){
$this->stmt = $this->dbh->prepare($query);
}
public function bind($param, $value, $type = null){
if(isnull($type)){
switch(true){
case is_int($value):
$type = PDO::PARAM_INT;
break;
case is_bool($value):
$type = PDO::PARAM_BOOL;
break;
case is_null($value):
$type = PDO::PARAM_NULL;
break;
default :
$type = PDO::PARAM_STR;
}
}
$this->stmt->bindValue($param, $value, $type);
}
public function execute(){
return $this->stmt->execute();
}
public function resultset(){
$this->execute();
return $this->stmt->fetchAll(PDO::FETCH_OBJ);
}
public function single(){
$this->execute();
return $this->stmt->fetch(PDO::FETCH_OBJ);
}
public function rowCount(){
return $this->stmt->rowCount();
}
public function lastInsertId(){
return $this->dbh->lastInsertId();
}
public function beginTransaction(){
return $this->dbh->beginTransaction();
}
public function endTransaction(){
return $this->bbh->commit();
}
public function cancelTransaction(){
return $this->dbh->rollBack();
}
}
?>
推荐答案
您在public function __contruct()
中有一个错字,应该是public function __construct() {
(您缺少s)
You have a typo in public function __contruct()
, it should be public function __construct() {
(you are missing an s)
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