稍微折騰了半天，摸索出了1.20版本注冊物品組的寫法

public class ModItems {

    public static final Item CITRINE = registerItem("citrine",
            new Item(new FabricItemSettings()),
            ItemGroups.BUILDING_BLOCKS);
    //這里只能寫ItemGroups里已經(jīng)有的物品組分類，我把這兩個添加到了建筑方塊分類中,新建物品組的代碼在另一個類中

    public static final Item RAW_CITRINE = registerItem("raw_citrine",
            new Item(new FabricItemSettings()),
            ItemGroups.BUILDING_BLOCKS);


    @SafeVarargs
    public static Item registerItem(String name, Item item, RegistryKey<ItemGroup>... itemGroups) {
        Item registerItem = Registry.register(Registries.ITEM, new Identifier("template-mod", name), item);
        for (RegistryKey<ItemGroup> itemGroup : itemGroups) {
            ItemGroupEvents.modifyEntriesEvent(itemGroup).register(entries -> {
                entries.add(registerItem);
            });
        }//下面的寫法除了變量類型不同幾乎沒變化
        return registerItem;
    }

    public static void registerModItems() {
        ExampleMod.LOGGER.debug("registering mod items for" + ExampleMod.MOD_ID);
    }
}

public class ModItemGroup {

    //這里構(gòu)建一個注冊物品組所需的RegistryKey
    public static RegistryKey<ItemGroup> TEMPLATEMOD = RegistryKey.of(RegistryKeys.ITEM_GROUP, new Identifier("template-mod"));

    public static void registerItemGroup() {
        //注冊物品組
        Registry.register(Registries.ITEM_GROUP, TEMPLATEMOD, ItemGroup.create(ItemGroup.Row.TOP, 3)
                //顯示的物品組名稱
                .displayName(Text.translatable("itemGroup.templatemod"))
                //物品組圖標(biāo)
                .icon(() -> new ItemStack(ModItems.CITRINE))
                //添加物品到物品組里面
                .entries((displayContext, entries) -> {
            entries.add(ModItems.CITRINE);
            entries.add(ModItems.RAW_CITRINE);
        }).build());
    }

    public static void registerModItemGroup() {
        ExampleMod.LOGGER.debug("registering mod item group for" + ExampleMod.MOD_ID);
    }
}