[NEW API]Help with Call to a member function ... on a non-object

Hello everyone, I began to developing my plugin for my server.
I'm developing my plugin for the new API and it came out a problem that I can not fix! (I use windows)

The console says: Call to a member function getOnlinePlayers () on a non-object ...

here is my code:
class main

PHP:

<?php
namespace Test;

use pocketmine\event\Listener;
use pocketmine\Player;
use pocketmine\plugin\PluginBase;
use pocketmine\Server;
use pocketmine\utils\TextFormat;

class main extends PluginBase implements Listener{
    public $timer;

    public function onLoad() {}
    public function onEnable(){  
        $this->getServer()->getPluginManager()->registerEvents($this, $this);
        $this->timer = new Timer($this);    
        $this->getServer()->getScheduler()->scheduleRepeatingTask($this->timer, 4800);
    }
    public function eventi(){
        //Call to a member function getOnlinePlayers() on a non-object
        $online = count($this->getServer()->getOnlinePlayers());
        Server::getInstance()->broadcastMessage("There are  ".$online." players ...");
    }
    public function onDisable(){}
}

class time

PHP:

<?php
namespace Test;

use pocketmine\scheduler\PluginTask;

class Timer extends PluginTask{
    public $main;
    public function onRun($currentTick){

        $this->main = new main($this);
        $this->main->eventi();  
    }
}

In the old API this code works

PHP:

$this->api->chat->broadcast("Now there are: ".count($this->api->player->getAll())." players online...");
                

how can fix this error?

PHP:

Server::getInstance()->broadcastMessage("Now there are : ". $online. " players online");


Try this :/

Thank you Falk, your solution works.
I have another problem, I can not update this short code of the old API to the new API

PHP:

case 'entity.health.change':
return false;
break; 

I tried searching in http://docs.pocketmine.net/ something about the player's health, but I did not find anything, could you help me please?

Because there is nine for that yet.

Also, never make a new plugin instance.

It won't work because PluginBase::init() isn't called anyways.

Thanks to everyone for the help