GUI containers

To skip straight to sample code for containers, see here (MBE30, MBE31).

A number of advanced blocks use "containers" - these are blocks that can store items, including

• chests
• crafting table
• furnaces

It is relatively easy to implement a custom container once you understand how the components fit together and communicate with each other.  As shown in the diagram below:

• The data about the container is stored in the TileEntity for that block.  Typical examples of the data are -what items are in the container, furnace fuel burning time & smelting time.
• The "master copy" of the TileEntity data is always on the server.  During initial load, and when chunk data is updated/resent, the client copy is updated as for normal TileEntities (using NBT in getDescriptionPacket() and onDataPacket() - see here.
• While the GUI is open, two extra classes are used to synchronise the data in real time and display it interactively to the user(s).  These are:
  a) GuiContainer, which specifies the layout of the GUI, retrieves items and other data (eg progress bars) for display, and interacts with the user.  The basic element of the GuiContainer is a number of "Slots" where items can be placed.
  b) Container, which collates the information from various sources into a single instance that the GUIContainer can use.  For example, the ContainerFurnace collates information from the TileEntityFurnace and player inventory.  It provides a consecutive list of Slots numbered from 0 .. N-1, where (eg) 0..35 might come from the player inventory, and 36 - 44 might come from the TileEntity.
• The Server Container is responsible for detecting changes to the Container that might need updating:
  a) for any clients which have the container open (eg multiple users accessing the same chest) - sendSlotContents() for items and sendProgressBarUpdate() for other data
  b) for other clients - marking the block for update (which then uses the getDescriptionPacket() / onDataPacket() to update the client copy
• Simple information can be sent from the client container to the server container using the crafters member variable of the container - icrafting.sendProgressBarUpdate() and icrafting.updateProgressBar().

The GuiContainer and Container are both generated by a single IGuiHandler-

• getServerGuiElement() for the server side Container
• getClientGuiElement() for the GuiContainer (which contains a Container during construction)

Communication between various parts of the container

The Container and GUIContainer combine elements from different data sources (TileEntity Items, Player Inventory Items, TileEntity extra data such as progress bars) into a single display