Addon and Mod API

The Javadocs of the latest unreleased version are available at https://appliedenergistics.github.io/javadoc/.

Mod Initialization

AE2 offers various extension points for your mod to hook into. The following table lists the API classes that are most relevant during mod initialization:
ClassPurpose
appeng.api.stacks.AEKeyTypesAddons can use this class to register custom storage types similar to AEItemKey and AEFluidKey.
appeng.api.networking.GridServicesAddons can register their own grid-wide services here.
appeng.api.movable.BlockEntityMoveStrategiesAllows mods to register custom strategies for moving block entities in and out of spatial storage.
appeng.api.features.GridLinkablesFor working with and adding items that can be linked to a grid in the security station.
appeng.api.storage.StorageCellsFor working with and adding items that serve as storage cells for grids.
appeng.api.features.LocatablesFor discovering security stations and quantum network bridges based on their unique keys, regardless of location.
appeng.api.parts.PartModelsFor registering JSON block models used by custom cable bus parts.
appeng.api.features.P2PTunnelAttunementFor registering new items that attune P2P tunnels to specific types when right-clicked.
appeng.api.client.StorageCellModelsFor customizing the models of storage cells when they're inserted into drives or ME chests.
In general, these classes are thread-safe and may be used directly in a mod's constructor or thereafter. Once initialization of mods has completed however, changes to these registries result in undefined behavior.
Since order of mod initialization on Fabric is undefined, addons that rely on AE2's items and blocks being registered will need to use the custom entrypoint defined by IAEAddonEntrypoint. See that classes javadoc for details.

Item and Fluid Keys

Item and fluid types are represented by keys in AE2. The AEKey class is the base for all keys, whether they represent items (AEItemKey) or fluids (AEFluidKey). Most of AE2s interfaces are generic in that they accept any AEKey, whether it is for a fluid or item.
Keys do not have counts since they don't represent a particular amount of items or fluid, they represent the type of item or type of fluid. As such, an item key consists of a reference to the Item and potential NBT data.
To represent a stack of some key, AE2 provides the utility class GenericStack. It consists of a key and an amount.
Each type of key is represented by an instance of AEKeyType, which is accessible via AEKey.getType(). It stores some properties common to all keys of a type (i.e. all item keys, or all fluid keys).
Keys can be saved to from NBT using toTagGeneric, which also stores a reference to their type so that AEKey.fromTagGeneric can restore the key of the correct type. The same mechanism can be used for packets with AEKey.writeToPacket and AEKey.readKey.
Sicne Java 16, the following patter makes it easy to work with generic keys when your code only supports items:
if (key instanceof AEItemKey itemKey) {
    ItemStack is = itemKey.toStack();
    // [...]
}

Grids and Nodes

AE2's core systems work by building grids from grid nodes that are created and owned by ingame objects such as block entities or parts. Grids are never created directly. They form and disband automatically by creating grid nodes, and connecting or disconnecting them.
NOTE: Grids a purely a server-side concept. They do not exist on the client.

Node Owners and Listeners

Every node is owned by an in-game object. An owner doesn't need to implement any particular interface. This makes it possible to integrate existing game objects with AE2 without having to introduce a hard dependency on it.
The node uses a listener (IGridNodeListener<T>) to interact with its owner. Both owner and listener have to be passed together to IGridHelper to create a node to allow the listener to be reused while still having type-safe access to the owner.
Example:
class MyBlockEntityListener implements IGridNodeListener<MyBlockEntity> {
    public static final MyBlockEntityListener INSTANCE = new MyBlockEntityListener();

    @Override
    public void onStateChanged(MyBlockEntity nodeOwner, IGridNode node, StateChangeReason reason) {
        [...]
        // for example: change block state of nodeOwner to indicate state
        // send node owner to clients
    }
}
class MyBlockEntity {
    // Create node with owner and listener
    private final IManagedNode mainNode = api.createManagedNode(
            this,
            MyBlockEntityListener.INSTANCE
    );
}

Managed Grid Nodes

The IGridHelper API offers a createManagedNode method to create an IManagedGridNode. Managed grid nodes simplify the lifecycle of creating and destroying grid nodes, and can be used to simplify the distinction between server and client, since they are available on the client-side as well. They will just not create the underlying node if they're being used on the client.
Your game object should notify the managed node about the following events:
  • Call destroy on the node when your game object is destroyed or its chunk unloaded.
  • Call create when the node can assume the owner is now in-world and ready to make outgoing connections (i.e. on its first tick).
  • When your game object loads from NBT data, load the node's stored data using loadFromNBT. This has to occur before you call create.
  • When your game object saves to NBT data, save the node's data using saveToNBT.

In-World Nodes

The main type of grid node are in-world grid nodes. They need to know their location and world when being created with IManagedGridNode.create(Level, BlockPos). External connections are automatically attempt to connect with adjacent in-world grid nodes by AE2 itself and do not need further handling.
In-world nodes can be selectively exposed on specific sides, or on all sides. The exposed sides can be changed after node creation and will automatically trigger a repathing.
To expose the actual IGridNode, it needs to be exposed by IManagedGridNode.getNode() through an appropriate way like capabilities.

Virtual Nodes

A special case are virtual nodes, which will not automatically form connection with other nodes. These allow addons to build ME networks outside the normal world for various reasons.
As these do not automatically establish connections, these have to be manually created with by using IGridHelper.createGridConnection(IGridNode, IGridNode). Removing a connection requires destroying the IGridNode, which also handles chunk unloading and ensures it leaving no old connections behind.

Node Services

The node's owner can add so-called services to a node, which can be used to add additional functionality or behavior to grid nodes. Services are represented by an interface that extends from IGridService.
Node services are often used by grid services to offer additional functionality to grid nodes that implement a specific service. These will be described in more detail in the description of the respective grid service.

Grid Services

Each grid provides several services to machines connected to the grid.
AE2 provides some services by default (see sub-interfaces of IGridService). Addons can register their own services using GridServices.
Services can be retrieved by calling IGrid#getService by passing the grid service's interface. For getting AE2's default services, IGrid offers several convenience methods.

Energy

Service Interface: IEnergyService
This service allows energy to be extracted from and injected into the grid's energy storage (i.e. energy cells, the grid's internal storage, etc.).

Ticking

Service Interface: ITickManager Convenience Getter: IGrid.getTickManager
AE2 offers its grid connected machines an advanced ticking system with the following features:
  • Ticking without being a tickable block entity
  • Variable tick rates
  • Putting devices to sleep if they run out of work
  • Waking sleeping devices in reaction to some event (i.e. neighbors changed)
The grid's ITickManager service handles the per-grid aspects of this ticking system. It offers an API to manage the sleep/wake status of grid nodes.
To participate in the ticking system, your grid node must provide the IGridTickable grid node service. The ITickManager reacts to the presence of this service when your grid node joins the grid.

Storage

Service Interface: IStorageService Convenience Getter: IGrid.getStorageService
This service allows nodes to notify listeners about changes to their inventory that are not caused by normal extraction/insertion, such as the external inventories (i.e. chests) changing their content.
Storage in grids is organized in "cells" which model inventories.
It also implements IStorageMonitorable to allow changes to the grid's inventory to be monitored.

Auto-Crafting

Service Interface: ICraftingService

Security

Service Interface: ISecurityService

Pathing

Service Interface: IPathingService

Spatial I/O

Service Interface: ISpatialService

Adding New Upgrades or Making Upgradable Machines

This will be made available in 10.0.0-beta.3.
Relevant APIs:
  • appeng.api.upgrades.Upgrades for managing upgrade cards and associating them with machines
  • appeng.api.upgrades.UpgradeInventories for creating upgrade inventories for use in upgradable machines or items

Custom Upgrade Cards

Each upgrade is unique identified by a registered item (the "upgrade card"). To create a custom upgrade card that behaves like the existing AE2 cards (i.e. it can be inserted into the network tool's toolbelt), use the utility function Upgrades#createUpgradeCardItem to create an item for your card. Remember it's your responsibility to actually register this item, provide an icon and a translation key for it. It will however, show the tooltip for supported machines and support insertion into machines by right-click out of the box.

Associating Upgrade Cards with Machines

For both cases where your addon adds a custom machine or upgrade card, you need to associate possible upgrades with potential machines. The Upgrades.add method allows you to link an upgrade card (represented by its Item) with a Machine (also represented by an item, usually a BlockItem or IPartItem).
If there are multiple machines that are treated equally with regard to upgrades, you can pass a translation key to the tooltipGroup parameter. When displaying the tooltip for an upgrade card, all supported machines with the same tooltipGroup will be merged into a single line and shown using the translation for the group. This was used for displaying fluid and item parts as one line, as well as the block/part form of interfaces.

Making custom Machines Upgradable

You can use the factory class UpgradeInventories to create inventories for storing upgrade cards. These inventories will use the provided item to identify which upgrade cards are accepted by the inventory to automatically prevent incompatible cards from being inserted.
They also offer convenience methods (see IUpgradeInventory) to quickly check if an upgrade is present or count how many upgrades of a type are present.
For the machine version created by forMachine, you are responsible for saving the inventory yourself from the change callback. For the item version created by forItem, the upgrade inventory will automatically save itself to the provided ┬┤ItemStack` whenever its content changes.

Changes from 1.17 and before to 1.18

There are large changes to the API in 1.18.
IAEStack, IAEItemStack and IAEFluidStack have been removed. The API now separates the "what" from the "how much" in that it uses AEKey to identify what is being transferred, while a separate method-argument is used for the amount.
The mapping is roughly as follows:
Old ClassNew Class
IAEStackGenericStack, AEKey
IAEItemStackGenericStack, AEItemKey
IAEFluidStackGenericStack, AEFluidKey
IStorageChannelAEKeyType
StorageChannelsAEKeyTypes
StorageChannels.items()AEKeyType.items()
StorageChannels.fluids()AEKeyType.fluids()
IMEInventoryMEStorage
IMEMonitorableMEMonitorStorage
IGuiItemIMenuItem (Use ItemMenuHost)
IPortableCellIPortableTerminal
ICraftingMediumICraftingMachine
ICellProviderIStorageProvider
getUnitsPerBytegetAmountPerByte
transferFactorgetAmountPerOperation
The network inventory is no longer channel specific. It contains items, fluids and potentially keys from addons at the same time. This also means IStorageMonitorable has become superfluous and was removed. IStorageMonitorableAccessor now gives direct access to the storage.
Stack watching has changed to only send the keys for which the stored amount has changed. This was done since the amounts reported to the watchers were never reliable to begin with, and were never used.
Craftable items are no longer reported as part of the network storage. It has been replaced by grid.getCraftingService().getCraftables(). NoOpKeyFilter is provided in case you want all types of keys, otherwise there are the convenience filters AEItemKey.filter() and AEFluidKey.filter() to only retrieve items or fluids.
Mounting storage into the network storage has been changed. Since storage has been unified across types, the storage service will now call mountInventories on the IStorageProvider service provided by any grid node and allow the node to "mount" storage into the network. When the node wants to remove or add storage due to an external event or config change, it can request the storage to repeat the mounting process by calling IStorageGrid.refreshNodeStorageProvider or using the utility provided in IStorageProvider.requestUpdate. This supersedes sending the GridCellArrayUpdate event.

Internal APIs

The following changes have been made to internal APIs, which may still be of interest to addons that depend on them.
Items that open AE GUIs are now more addon friendly. The ItemMenuHost class can be used as an easy way to implement a menu host for hosting terminals and other menus.
The priority and crafting confirm menus now use a generic system for returning to the previous screen. Your part, block entity or item menu host needs to implement ISubMenuHost for this to work.
Custom storage cells have been simplified, and the same class can be used to create addon storage cells for any stored item key. Due to the storage math still being different for items and fluids, there are still key-type specific cells, which are all based on the same class BasicStorageCell, which doesn't have a guaranteed API however (this is an improvement for later).