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tutorial:blockentity_modify_data

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tutorial:blockentity_modify_data [2025/04/01 12:30] – update solidblocktutorial:blockentity_modify_data [2025/04/01 12:48] (current) – [Some notes about NbtCompound] solidblock
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 In the previous tutorial, we have created a [[blockentity|block entity]]. But they are too boring as they do not have any data. Therefore, we try to add some data to it, and define ways of serializing and deserializing data. In the previous tutorial, we have created a [[blockentity|block entity]]. But they are too boring as they do not have any data. Therefore, we try to add some data to it, and define ways of serializing and deserializing data.
  
 +===== Some notes about NbtCompound =====
 +
 +Since 1.21.5, methods of ''NbtCompound'' have been changed. The getter methods return ''Optional'' objects, unless you specify another parameter as a default value used when the field does not exist. For example:
 +
 +<code java>
 +// no default value specified, returns Optional
 +Optional<Integer> value = nbt.getInt("value"); // not OptionalInt
 +
 +// default value specified, returns the default value when the field does not exist
 +int value = nbt.getInt("value", 1000);
 +</code>
 +
 +For collection types, such as compounds and lists, an empty object can be returned as a default value, for example:
 +<code java>
 +// no default value specified, returns Optional
 +Optional<NbtCompound> config = nbt.getCompound("config");
 +
 +// when the field does not exist, returns an empty compound
 +NbtCompound config = nbt.getCompoundOrEmpty("config");
 +</code>
 +
 +In versions before 1.21.5, they return zero or empty values. If you need to specify a default value, you need to judge with ''contains'' method beforehand. For example:
 +<code java>
 +// returns 0 if the field does not exist:
 +int value = nbt.getInt("value");
 +
 +// returns an empty compound when the field does not exist:
 +NbtCompound config = nbt.getCompound("config");
 +</code>
 +
 +Besides, since 1.21.5, the whole NBT compound and its fields can be decoded directly with [[codec]]s, such as:
 +<code java>
 +NbtCompound nbt = new NbtCompound();
 +nbt.put("Id", Identifier.CODEC, Identifier.of("tutorial", "example_id"));
 +Optional<Identifier> id = nbt.get("Id", Identifier.CODEC);
 +</code>
 +
 +<code java>
 +NbtCompound nbt = new NbtCompound();
 +// have to use the RegistryOps since an item is a registry entry
 +nbt.copyFromCodec(ItemStack.MAP_CODEC, wrapperLookup.getOps(NbtOps.INSTANCE), new ItemStack(Items.WHEAT));
 +Optional<ItemStack> stack = nbt.decode(ItemStack.MAP_CODEC, wrapperLookup.getOps(NbtOps.INSTANCE));
 +</code>
 +
 +Besides, since 1.21.5, lists support mixing elements of different types. In previous versions, mixing elements of different types in a list results in exceptions.
 +
 +More information about NBT changes, see [[https://fabricmc.net/2025/03/24/1215.html|Fabric for Minecraft 1.21.5]].
 ===== Serializing Data ===== ===== Serializing Data =====
  
tutorial/blockentity_modify_data.1743510615.txt.gz · Last modified: 2025/04/01 12:30 by solidblock