When the player clicks a GUI. I'm causing this GUI giving the player an item in the inventory:

 

ItemStack item = player.inventory.getStackInSlot(player.inventory.currentItem);
        player.inventory.setInventorySlotContents(emptySlot, item);
        player.inventory.setInventorySlotContents(player.inventory.currentItem, scepter);
        player.inventory.markDirty();

 

in the currentItem slot and I switch the old item to an old slot.

But when I right click with the new item, it still tries to place the old block.

 

You can't change anything that has to do with world data on client-side

The client can't modify data on the server side, so you have to use packets to send a signal to the server to change the

ItemStack

on the player.

Shouldn't "markDirty()" cause such a package sending?

 

Isn't there a precoded message which does update the inventory?

Shouldn't "markDirty()" cause such a package sending?

No, that's probably for server -> client synchronization

Isn't there a precoded message which does update the inventory?

I don't know, but I do know that that's not what you need. You need to make custom packets to send a signal from the client to the server when the user wants to change the item, and change the item on the server side when the packet is received.

Yeah I know how the packets work but I hoped deep inside my heart that I don't have to create one more of these messages =D