ViaFabricPlus/documentation/DEVELOPER_API.md

Developer API

There is no real addon base, to create addons you can simply use the event system, which uses Fabric's Event-API.

public class ViaFabricPlusExampleAddon implements ClientModInitializer {

  @Override
  public void onInitializeClient() {
    ChangeProtocolVersionCallback.EVENT.register(versionEnum -> {
      System.out.println("Version changed to " + versionEnum.getName());
    });
  }
}

ViaFabricPlus has 7 events at the moment:

Callback class name	Description
ChangeProtocolVersionCallback	Called when the user changes the target version in the screen, or if you connect to a server for which a specific version has been selected, you disconnect, the event for the actual version is also called.
FinishMinecraftLoadCallback	Called when Minecraft is finished with loading all its components
FinishViaVersionStartupCallback	Called when ViaVersion is loaded and ready to use
InitializeSettingsCallback	Called after the default setting groups are loaded and before the setting config is loaded
LoadClassicProtocolExtensionCallback	Called when the classic server sends the protocol extensions (only in c0.30 CPE)
PreLoadCallback	Called before everything (Pre-pre load)
DisconnectConnectionCallback	Called when the user disconnects from a server.

General API

Add CustomPayload channels for versions below 1.13

In order to receive custom payloads with custom channels in versions below 1.13, you need to register them, that's what you do:

Protocol1_13To1_12_2.MAPPINGS.getChannelMappings().put("FML|HS", "fml:hs");

Get the release version of a material:

final VersionRange range = ItemReleaseVersionDefinition.INSTANCE.getItemMap().get(Items.WRITABLE_BOOK); // If an item does not appear in the item map, it has always existed

// The Range class then contains all versions in which the item occurs. 
// https://github.com/ViaVersion/ViaLoader

Creating own settings for the settings screen:

public class ExampleSettingGroup extends SettingGroup {
    public static final ExampleSettingGroup INSTANCE = new ExampleSettingGroup();
    
    public final BooleanSetting test = new BooleanSetting("Test", false);
    
    public ExampleSettingGroup() {
        super("Example");
    }
}

and then you register the setting group in your onLoad method:

PreLoadCallback.EVENT.register(() -> {
    ViaFabricPlus.INSTANCE.getSettingsSystem().addGroup(ExampleSettingGroup.INSTANCE);
});

Implementing custom classic protocol extensions:

public class ExampleExtensionSupport implements ClientModInitializer {

  public static ClientboundPacketsc0_30cpe EXT_CLICK_DISTANCE;

  @Override
  public void onInitializeClient() {
    PreLoadCallback.EVENT.register(() -> {
      CustomClassicProtocolExtensions.allowExtension(ClassicProtocolExtension.CLICK_DISTANCE); // Register extension as supported

      EXT_CLICK_DISTANCE = CustomClassicProtocolExtensions.createNewPacket(ClassicProtocolExtension.CLICK_DISTANCE, 0x12, (user, buf) -> buf.readShort());
    });

    FinishViaLoadingBaseStartupCallback.EVENT.register(() -> {
      Via.getManager().getProtocolManager().getProtocol(Protocolc0_30toc0_30cpe.class).registerClientbound(EXT_CLICK_DISTANCE, null, new PacketHandlers() {
        @Override
        protected void register() {
          handler(wrapper -> {
            wrapper.cancel();
            final short distance = wrapper.read(Type.SHORT);
            // Do your stuff...
          });
        }
      }, true);
    });
  }
}