Solved Damage by explosion

Hello,
I would like to know how to cancel a damage on a player who place a TNT and the players approximate receive a damage.


Here my code but I don't know why the explosion doesnt cancelled.

PHP:

public $placer = [];

    public function onBlockPlace(BlockPlaceEvent $e)
    {
        $p = $e->getPlayer();
        $b = $e->getBlock();

         if($b->getId() === 46){
           $this->placer[$p->getName()] = $p->getName();

        }
    }

    public function onHit(EntityDamageEvent $e)
    {
        $victim = $e->getEntity();

        if (!$victim instanceof Player) {
            return;
        }

        if ($e instanceof EntityDamageByChildEntityEvent) {

            if($e->getCause() === 9 && isset($this->placer[$victim->getName()])) {
                    $e->setCancelled();
             }
         }
     }