Hi, Ive been making an armour mod, where the armour needs to store some nbt data. The data is attached to it via actions in a gui. The only thing is - when the nbt is changed through the gui, the data doesnt seem to sync untill I pick the item from my inventory and put it back. If I relog, the data is gone, if I drop it by pressing 'Q' the data is gone. However if I move it to a different slot, or just drop it manually (as in pick it from the inventory and click outside the gui) the data stays. I presume its something about the nbt not getting synced until the item is interacted with, but my question is why and what do I do with it? Any help will be much appreciated

Yup, that is right.

 

Few rules:

 

1. Data manipulation must always happen on server.

2. Gui is client-only!

3. In every case of guis that are supposed to edit something - you will ALWAYS send a packet.

General design:

* Gui action (e.g buton click)

* Client packet to server

* Server handles packet (note: thread safety)

* Server checks agains requirements (if it is legal for player to do such edit)

* Server modifies given ItemStack and client gets update.

 

4. Now here is a big note: (which you probably know)

Whenever there is ItemStack on display (in gui) - there is also Container which handles syncing ItemStacks' visible in-container positions. When ItemStack would get edited on server without notifying - client will stay with old data (that's why it would get updated once you actually move it). Logically - after editing ItemStack on server (from mentioned packet) you will need to notify change. You pretty much do that manually (by sending packet server -> client wth update of stack at given slot in current container which can be accessed from player instance) or you could probably use some internal thing - lookup Container code such as transferStackInSlot and other (which I think does those).

 

5. Now - you may ask - "If I do it (change) on client-only, why it sometimes gets saved?" - well, if nothing changed since I was hanving fun with it - just change your game mode (creative game mode allows bi-directional ItemStack updates) - that is if nothing changed.

Thanks for the reply! Thats a lot of info

Some of it I knew, but not all. Well, I guess I'll have to go read up about custom packets, as I know the theory but haven't ever actually used them...

Oh and the change to creative thing does still work