Fabric Wiki

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====== Modding Tips ======

Here's a collection of assorted Fabric-related modding tips gleaned from experiences on advising users of the API.

===== Basics (API) =====

  * Due to the injection-based approach of Fabric's API development, we don't tend to patch classes outright in a way visible to the end user. As such, you may occasionally find Fabric extensions of vanilla classes when you run into something you cannot do. For example:
    * Block.Settings -> FabricBlockSettings (except 1.20.5)
    * EntityType.Builder -> FabricEntityTypeBuilder
  * For a built-in resource pack or data pack, please ensure that an "assets/[mod id]" or "data/[mod id]" directory path is present, respectively! IDEA users might find themselves accidentally creating an "assets.[mod id]" directory - this won't work.

===== Mixins =====

  * To cast a class to an interface it doesn't implement, or cast a final class, or cast the mixin to your target class, you can use the "(TargetClass) (Object) sourceClassObject" trick.
  * @Redirect and @ModifyConstant mixins cannot currently be nested (applied by more than one mod in the same area at the same time). This might change later in development - however, for now, alongside @Overwrite, please avoid them if possible (or discuss bringing the hook over to Fabric's API, or - for more niche things - consider putting it in a small JAR-in-JAR API).
  * If you're adding non-private custom fields or methods, prefix them with "[modid]$" or another unique string and annotate them with @Unique. Essentially, "mymod$secretValue" instead of "secretValue". This is to avoid conflicts between mods adding a field or method named the same way.

===== Networking =====

  * Packets always begin execution on the **network thread**, however accesses to most Minecraft things are not thread-safe. In general, if you're not exactly sure what you're doing, you want to parse the packet on the network thread (read all the values out), then use the **task queue** to perform additional operations on the **main server/client thread**.

===== Pitfalls =====

  * Avoid using the ''java.awt'' or ''javax.swing'' package and their subpackages. AWT does not work well on all systems. Several users have reported that it hangs Minecraft.