I am trying to add a custom condition that checks whether item exists in registry.

an easy example is holder items that provide no functionality.

my exact needs are I am going to be making my mod a modular installation through the use of the config file. players can enable/disable parts of the mod.

what I need help with is how to go about creating the class and how to register it.

if you want recipes to reference other mod's item (other mod being optional and recipe not crashing the game), use forge's mod_loaded condition. look inside the jar file of "create" mod, for example in smelting recipes directory - you'll find smelting recipes that give players lead ingots even though the mod doesn't include lead ingots.

if you want the recipe dependent on a switch in your config file, make a condition class....

Spoiler

public class OptionalRecipeCondition implements ICondition
{
	/// constructor, etc.

	@Override
	public boolean test()
	{
		// this works for single option; 
		// you could check for option name to reuse this class
		return OptionsHolder.COMMON.SomethingSomething.get();
	}

	/////////////////////////////////////////////////////

	public static class Serializer implements IConditionSerializer<OptionalRecipeCondition>
	{
		private final ResourceLocation conditionId;

		public Serializer(ResourceLocation id)
		{
			this.conditionId = id;
		}

		@Override
		public void write(JsonObject json, OptionalRecipeCondition condition)
		{
			// if you have parameters, write them like this: json.addProperty("something", condition.something);
		}

		@Override
		public OptionalRecipeCondition read(JsonObject json)
		{
			return new OptionalRecipeCondition(this.conditionId, json.getAsJsonPrimitive("param1").getAsString(), etc));
		}

		@Override
		public ResourceLocation getID()
		{
			return this.conditionId;
		}
	}
}

 

...and then in the main class (mod class), in FMLCommonSetupEvent do
CraftingHelper.register(new OptionalRecipeCondition.Serializer(new ResourceLocation(YourThing.MODID, "optional")));

this last string ("optional" in example above) is the type that is stated in recipe json.

Edited January 11, 20223 yr by MFMods
added spoiler tag

I have tried this to no avail even when the test returns true the recipe is still absent

remove the condition part of the recipe. does it then work in game?

Yes it does work when the condition is removed