Registries
Registration is the process of taking the objects of a mod (such as items, blocks, sounds, etc.) and making them known to the game. Registering things is important, as without registration the game will simply not know about these objects, which will cause unexplainable behaviors and crashes.
Most things that require registration in the game are handled by the Forge registries. A registry is an object similar to a map that assigns values to keys. Forge uses registries with ResourceLocation
keys to register objects. This allows the ResourceLocation
to act as the “registry name” for objects. The registry name for an object may be accessed with #getRegistryName
/#setRegistryName
. The setter can only be called once; calling it twice results in an exception.
Every type of registrable object has its own registry. To see all registries supported by Forge, see the ForgeRegistries
class. All registry names within a registry must be unique. However, names in different registries will not collide. For example, there’s a Block
registry, and an Item
registry. A Block
and an Item
may be registered with the same name example:thing
without colliding; however, if two different Block
s or Item
s were registered with the same exact name, the second object will override the first.
Methods for Registering
There are two proper ways to register objects: the DeferredRegister
class, and the RegistryEvent.Register
lifecycle event.
DeferredRegister
DeferredRegister
is the newer and documented way to register objects. It allows the use and convenience of static initialisers while avoiding the issues associated with it. It simply maintains a list of suppliers for entries and registers the objects from those suppliers during the proper RegistryEvent.Register
event.
An example of a mod registering a custom block:
private static final DeferredRegister<Block> BLOCKS = new DeferredRegister<>(ForgeRegistries.BLOCKS, MODID);
public static final RegistryObject<Block> ROCK_BLOCK = BLOCKS.register("rock", () -> new Block(Block.Properties.create(Material.ROCK)));
public ExampleMod() {
BLOCKS.register(FMLJavaModLoadingContext.get().getModEventBus());
}
Register
events
The RegistryEvent
s are the second and more flexible way to register objects. These events are fired after the mod constructors and before the loading of configs.
The event used in registering objects is the RegistryEvent.Register<T>
. The type parameter T
should be set to the type of the object being registered. Calling #getRegistry
will return the registry, upon which objects are registered with #register
or #registerAll
.
Here is an example: (the event handler is registered on the mod event bus)
@SubscribeEvent
public void registerBlocks(RegistryEvent.Register<Block> event) {
event.getRegistry().registerAll(new Block(...), new Block(...), ...);
}
Note
Some classes cannot by themselves be registered; instead, *Type
classes are registered, and used in the formers’ constructors. For example, TileEntity
has TileEntityType
, and Entity
has EntityType
. These *Type
classes are factories that simply create the containing type on demand.
These factories are created through the use of their *Type.Builder
classes. An example: (REGISTER
refers to a DeferredRegister<TileEntityType>
)
public static final RegistryObject<TileEntityType<ExampleTile>> EXAMPLE_TILE = REGISTER.register(
"example_tile", () -> TileEntityType.Builder.create(ExampleTile::new, EXAMPLE_BLOCK.get()).build(null)
);
Referencing Registered Objects
Registered objects should not be stored in fields when they are created and registered. They are to be always newly created and registered whenever their respective RegistryEvent.Register
event is fired. This is to allow dynamic loading and unloading of mods in a future version of Forge.
Registered objects must always be referenced through a RegistryObject
or a field with @ObjectHolder
.
Using RegistryObjects
RegistryObject
s can be used to retrieve references to registered objects once they are available. These are used by DeferredRegister
to return a reference to registered objects. Their references are updated after their corresponding registry’s RegistryEvent.Register
event is fired, along with the @ObjectHolder
annotations.
To get a RegistryObject
, call RegistryObject.of
with a ResourceLocation
and the IForgeRegistry
of the registrable object. Custom registries can also be used through giving a supplier of the object’s class. Store the RegistryObject
in a public static final
field, and call #get
whenever you need the registered object.
An example of using RegistryObject
:
public static final RegistryObject<Item> BOW = RegistryObject.of(new ResourceLocation("minecraft:bow"), ForgeRegistries.ITEMS);
// assume that ManaType is a valid registry, and 'neomagicae:coffeinum' is a valid object within that registry
public static final RegistryObject<ManaType> COFFEINUM = RegistryObject.of(new ResourceLocation("neomagicae", "coffeinum"), () -> ManaType.class);
Using @ObjectHolder
Registered objects from registries can be injected into the public static
fields by annotating classes or fields with @ObjectHolder
and supplying enough information to construct a ResourceLocation
to identify a specific object in a specific registry.
The rules for @ObjectHolder
are as follows:
- If the class is annotated with
@ObjectHolder
, its value will be the default namespace for all fields within if not explicitly defined - If the class is annotated with
@Mod
, the modid will be the default namespace for all annotated fields within if not explicitly defined - A field is considered for injection if:
- it has at least the modifiers
public static
; - one of the following conditions are true:
- the enclosing class has an
@ObjectHolder
annotation, and the field isfinal
, and:- the name value is the field’s name; and
- the namespace value is the enclosing class’s namespace
- An exception is thrown if the namespace value cannot be found and inherited
- the field is annotated with
@ObjectHolder
, and:- the name value is explicitly defined; and
- the namespace value is either explicitly defined or the enclosing class’s namespace
- the enclosing class has an
- the field type or one of its supertypes corresponds to a valid registry (e.g.
Item
orArrowItem
for theItem
registry); - An exception is thrown if a field does not have a corresponding registry.
- it has at least the modifiers
- An exception is thrown if the resulting
ResourceLocation
is incomplete or invalid (non-valid characters in path) - If no other errors or exceptions occur, the field will be injected
- If all of the above rules do not apply, no action will be taken (and a message may be logged)
@ObjectHolder
-annotated fields are injected with their values after their corresponding registry’s RegistryEvent.Register
event is fired, along with the RegistryObject
s.
Note
If the object does not exist in the registry when it is to be injected, a debug message will be logged and no value will be injected.
As these rules are rather complicated, here are some examples:
@ObjectHolder("minecraft") // Inheritable resource namespace: "minecraft"
class AnnotatedHolder {
public static final Block diamond_block = null; // No annotation. [public static final] is required.
// Block has a corresponding registry: [Block]
// Name path is the name of the field: "diamond_block"
// Namespace is not explicitly defined.
// So, namespace is inherited from class annotation: "minecraft"
// To inject: "minecraft:diamond_block" from the [Block] registry
@ObjectHolder("ambient.cave")
public static SoundEvent ambient_sound = null; // Annotation present. [public static] is required.
// SoundEvent has a corresponding registry: [SoundEvent]
// Name path is the value of the annotation: "ambient.cave"
// Namespace is not explicitly defined.
// So, namespace is inherited from class annotation: "minecraft"
// To inject: "minecraft:ambient.cave" from the [SoundEvent] registry
// Assume for the next entry that [ManaType] is a valid registry.
@ObjectHolder("neomagicae:coffeinum")
public static final ManaType coffeinum = null; // Annotation present. [public static] is required. [final] is optional.
// ManaType has a corresponding registry: [ManaType] (custom registry)
// Resource location is explicitly defined: "neomagicae:coffeinum"
// To inject: "neomagicae:coffeinum" from the [ManaType] registry
public static final Item ENDER_PEARL = null; // No annotation. [public static final] is required.
// Item has a corresponding registry: [Item].
// Name path is the name of the field: "ENDER_PEARL" -> "ender_pearl"
// !! ^ Field name is valid, because they are
// converted to lowercase automatically.
// Namespace is not explicitly defined.
// So, namespace is inherited from class annotation: "minecraft"
// To inject: "minecraft:ender_pearl" from the [Item] registry
@ObjectHolder("minecraft:arrow")
public static final ArrowItem arrow = null; // Annotation present. [public static] is required. [final] is optional.
// ArrowItem does not have a corresponding registry.
// ArrowItem's supertype of Item has a corresponding registry: [Item]
// Resource location is explicitly defined: "minecraft:arrow"
// To inject: "minecraft:arrow" from the [Item] registry
public static Block bedrock = null; // No annotation, so [public static final] is required.
// Therefore, the field is ignored.
public static final ItemGroup group = null; // No annotation. [public static final] is required.
// ItemGroup does not have a corresponding registry.
// No supertypes of ItemGroup has a corresponding registry.
// Therefore, THIS WILL PRODUCE AN EXCEPTION.
}
class UnannotatedHolder { // Note the lack of an @ObjectHolder annotation on this class.
@ObjectHolder("minecraft:flame")
public static final Enchantment flame = null; // Annotation present. [public static] is required. [final] is optional.
// Enchantment has corresponding registry: [Enchantment].
// Resource location is explicitly defined: "minecraft:flame"
// To inject: "minecraft:flame" from the [Enchantment] registry
public static final Biome ice_flat = null; // No annotation on the enclosing class.
// Therefore, the field is ignored.
@ObjectHolder("minecraft:creeper")
public static Entity creeper = null; // Annotation present. [public static] is required.
// Entity does not have a corresponding registry.
// No supertypes of Entity has a corresponding registry.
// Therefore, THIS WILL PRODUCE AN EXCEPTION.
@ObjectHolder("levitation")
public static final Potion levitation = null; // Annotation present. [public static] is required. [final] is optional.
// Potion has a corresponding registry: [Potion].
// Name path is the value of the annotation: "levitation"
// Namespace is not explicitly defined.
// No annotation in enclosing class.
// Therefore, THIS WILL PRODUCE AN EXCEPTION.
}
Creating Custom Registries
Custom registries are created by using RegistryBuilder
during the RegistryEvent.NewRegistry
event. The class RegistryBuilder
takes certain parameters (such as the name, the Class
of its values, and various callbacks for different events happening on the registry). Calling RegistryBuilder#create
will result in the registry being built, registered to the RegistryManager
, and returned to the caller for additional processing.
The Class
of the value of the registry must implement IForgeRegistryEntry
, which defines that #setRegistryName
and #getRegistryName
can be called on the objects of that class. It is recommended to extend ForgeRegistryEntry
, the default implementation instead of implementing the interface directly. When #setRegistryName(String)
is called with a string, and that string does not have an explicit namespace, its namespace will be set to the current modid.
The Forge registries can be accessed through the ForgeRegistries
class. All registries, Forge-provided or custom, can be retrieved by calling GameRegistry.findRegistry(Class)
with the appropriate class for the registry. For example, the registry for Block
s can be retrieved by calling GameRegistry.findRegistry(Block.class)
.