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[1.11.2] [Partially Solved] Update player inventory from the client


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I'm working on a client-side-only mod which allows the user to edit an item in his inventory when he's in Creative Mode. Since I'm not adding any content (blocks, items) and only a GUI, I guess I don't have to handle the server part.
But when I edit an item, the changes are saved on the client side but not on the server side. Which means that when I drop the edited item and take it back in my inventory, changes don't apply.
Is there a way to tell to the server that the item has to be updated, without using custom packets so my mod can stay client-side-only ?


Or must I do all the changes on the server side and use Custom Packets ?

Edited by Franckyi
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4 minutes ago, Franckyi said:

Another question, can I modify a block (placed in the world) or an entity without using custom packets from the client ?

As long as the player could normally do it (i.e. within reach distance), yes. You'll have to look at which packets are sent when the player mines a block.

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Huh, I'm having trouble updating the inventory on the server side.

It seems that the modified item is being placed in the survival crafting grid, instead of where it should be. I used debug mode and the slot ID used when instantiating CPackedCreativeInventoryAction is correct.

In NetHandlerPlayServer::processCreativeInventoryAction, the packet data is still correct. When this.player.inventoryContainer.putStackInSlot is called, the Container::getSlot returns a slot from an InventoryCrafting inventory. Which is strange because the item should be in my main hand.
Any thoughts about this ? Am I not using CPackedCreativeInventoryAction correctly ?

Also, I don't understand this line in NetHandlerPlayServer::processCreativeInventoryAction :

boolean flag1 = packetIn.getSlotId() >= 1 && packetIn.getSlotId() <= 45;

Why is it checking for a slot ID higher or equal to 1 ? Why is the item dropped if my slot ID is equal to 0 (representing the first hotbar slot) ?

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I am really not sure. The creative mode code is a giant mess.

The hotbar you see in the creative menu is the same hotbar you see in survival, they are based on the same inventory.


I checked the code more and CPacketCreativeInventoryAction does not do what I thought it did. It seems to somehow set the server-side survival inventory to whatever is currently in the creative scroll menu, so that it can then be picked up on the client. I have no idea. You'll have to muck around with the code in GuiContainerCreative, which honestly I cannot be bothered to do, because it is a giant mess.

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  • 2 months later...

I'm sorry to revive this thread, but this is something I am kind of knowledgeable about, having made two mods that deals with clientside item editing. For one of them, I pretty much rewrote the creative gui (altering it to my needs).

Now, I've moved on from using that, but I still use the CPacketCreativeInventoryAction packet.


Here's how:

			int slot = mc.player.inventory.currentItem;
			mc.playerController.sendSlotPacket(stack, 36 + slot);


To understand the index, you need to look at ContainerPlayer:

The first 5 slots are for crafting

The next 4 is for armor and offhand

That means the actual inventory starts a 9. The actionbar starts at 27+9=36, which is what I use to override my current item.

Beware that some servers alter the packet processing to require certain permissions for certain item, which the vanilla servers doesn't do.


Feel free to contact me on discord Ruukas#9050, if you have any other questions related to this kind of stuff.


If you use custom packets, that defeats the purpose of having a clientside mod, doesn't it?

Edited by Ruukas
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