Inventory Size

PHP:

<?php

namespace MF;

use pocketmine\plugin\PluginBase;
use pocketmine\Player;
use pocketmine\Inventory;
use pocketmine\command\Command;
use pocketmine\command\CommandSender;
use ngocchinhofficial\NapThe\NapThe;
use ngocchinhofficial\NapThe\NapTheAPI;
use pocketmine\event\player\PlayerRespawnEvent;
use pocketmine\Server;

Class IS extends PluginBase{
   
    public $napThe;

public function onEnable(){
    $this->napThe = $this->getServer()->getPluginManager()->getPlugin("NapThe");
}

public function onCommand(CommandSender $sender, Command $cmd, $label, array $args){
        switch($cmd->getName()){
          case "isize":
            $sender->getInventory()->setSize(45);
            $sender->sendMessage("§8[§eInventory§8] §fТúi đồ của bạn tăng 45 chỗ trống");      
                 $this->saveYml();          
          return true;
     
          case "isize1":
            if (!$this->napThe->api->take($sender->getName(), abs(35))){
            $sender->sendMessage("§a- Không đủ Point để tăng thêm kho");
            return false;
        }
            $sender->getInventory()->setSize(65);
            $sender->sendMessage("§8[§eInventory§8] §fТúi đồ của bạn tăng 65 chỗ trống");
             $this->saveYml();
          return true;
     
          case "isize2":
            if (!$this->napThe->api->take($sender->getName(), abs(40))){
            $sender->sendMessage("§a- Không đủ Point để tăng thêm kho");
            return false;
        }
            $sender->getInventory()->setSize(70);
            $sender->sendMessage("§8[§eInventory§8] §fТúi đồ của bạn tăng 70 chỗ trống");  
            $this->saveYml();          
          return true;
          default:
               return false;
}
}
public function onDisable(){}
}
?>

This is my code
And how to save inventory size when player join

 

Use player join event