Cancel InventoryTransactionEvent

How can I cancell InventoryTransactionEvent, when player change hotbar item?
For example, I would like, that clock always were in first Invntory bar slot.

Something like this?

PHP:

public function onSlotChange(InventoryTransactionEvent $event) {
        $newItem = null;
        $player = null;
        $transactions = $event->getQueue()->getTransactions();
        foreach ($transactions as $tr){
                if ($tr->getTargetItem() instanceof Item) $newItem = $tr->getTargetItem();
                if ($tr->getInventory() instanceof PlayerInventory) $player = $tr->getInventory()->getHolder();
        }
        if ($player != null && $newItem != null){
                $lastItem = $player->getInventory()->getItemInHand();
                if ($lastItem->getId() == 347 && $newItem->getId() != 347){ //compas
                    $event->setCancelled();
                }
        }
}


 

Ops, event is works. I.e items don't drop, but items remove from Invntory bar, and appear in player inventory ;C