[PHP] pobierz, plaintext 
<?php
 
class db
{
    private $host;
    private $user;
    private $pass;
    private $db_name;
    private $name_tabl;
 
    public function __construct($HOST, $USER, $PASS, $DB_NAME, $NAME_TABL)
    {
        $this->host = $HOST;
        $this->user = $USER;
        $this->pass = $PASS;
        $this->db_name = $DB_NAME;
        $this->name_tabl = $NAME_TABL;
    }
 
    private function connectDb()
    {
        $conn = new mysqli($this->host, $this->user, $this->pass, $this->db_name);
 
        return $conn;
    }
 
    private function queryTable()
    {
        return $this->connectDb->query('SELECT * FROM ' . $this->name_tabl);
    }
 
    public function printNameColums()
    {
        $finfo = mysqli_fetch_fields($this->queryTable());
 
        foreach ($finfo as $val)
        {
 
            return "<th>" . $val->name . "</th>";
        }
 
 
    }
 
}
 
$a = new db('localhost', 'root', 'wsk123', 'nauka', 'pracownicy');
echo $a->printNameColums();
 
?>
[PHP] pobierz, plaintext 

Notice: Undefined property: db::$connectDb in C:\xampp\htdocs\ajax\showDb.php on line 29

Fatal error: Call to a member function query() on a non-object in C:\xampp\htdocs\ajax\showDb.php on line 29

a nie

[PHP] pobierz, plaintext 
return $this->connectDb()->query('SELECT * FROM ' . $this->name_tabl);
[PHP] pobierz, plaintext 

?

Tak zabrakło () . Dzięki

wiesz jaki jest teraz problem z Twoim kodem?

za kazdym razem gdy wywolujesz $this->connectDb() tworzysz obiekt polaczenia.

obiekt polaczenia stworz tylko raz i przypisz go do skladowej klasy a pozniej
zwracaj tylko ta skladowa:

[PHP] pobierz, plaintext 
 private function connectDb()
{
if (is_null($this->conn)) $this->conn = new mysqli($this->host, $this->user, $this->pass, $this->db_name);
return $this->conn;
}
[PHP] pobierz, plaintext