如何从另一个类调用Connection Class？

Question

how can I call DbConnect class and use it for another class like FormElement class ?

main.class.php

class DBCONNECT
{
   public $dbConnection;

   public function __construct($dbHost, $dbUsername, $dbPassword, $dbName){

       $this->dbConnection = new mysqli($dbHost, $dbUsername, $dbPassword, $dbName);

       if($this->dbConnection->error){
           trigger_error("Sorry couldn't connect to database :("); // problem connect to database
       }else{
           return true; // connection successfully
       }
    }
}

and my another class was

element.class.php

class FormElement
{
   public function getCmbPovinsi(){
    $userSqlQuery   = "SELECT id,provinsi FROM aud_provinsi ORDER BY provinsi";
    $userSys        = $this->dbConnection->query($userSqlQuery) or die($this->dbConnection->error);

    if ($userSys) {
        /* checking for available users */
        if($userSys->num_rows > 0){
            echo'<div class="col_one_fourth">
                    <label for="provinsi">Provinsi<small>*</small></label>
                        <select id="provinsi" name="provinsi" class="sm-form-control required">
                            <option value="">-- Pilih Provinsi --</option>';

                    while ($userResult = $userSys->fetch_assoc()) {
                        echo '<option value="'.$userResult['id'].'">'.$userResult['provinsi'].'</option>';          
                    }
                    echo '</select>
                 </div>';
        }else{
            echo "Error Handling!!";
        }
    }else{
        echo "invalid query : ".$this->dbConnection->error."<br>";
        echo "whole query : ".$userQuery ."<br>";
    }               
  }
}

and how this code can work properly ?

Answer 1

In element.class.php first require main.class.php PATH.

# element.clas.php #

require 'main.class.php';

class FormElement
{
  protected $connection;

   public function __construct(DBCONNECT $connection)
   {
     $this->connection = $connection;
   }

   public function getCmbPovinsi()
   {
     ...
     $this->connection->query(...);
   }

}

This method is called dependency injection. Now when you want to use element you can create an object like this:

$element = new FormElement(new DBCONNECT("host", "username", "password", "db"));