Hello, I'm working on implementing a capability for living entities for a mod I'm working on and I've run into some trouble. I believe I've gotten most of it right, from what I've gathered from other threads here.

 

The trouble I'm running into is when the AttachCapabilitiesEvent<Entity> I'm hooking into fires. When that event fires, I'm calling event.addCapability(), and the game crashes while it's attempting to create the new instance of my capability provider (ICapabilitySerializable), throwing a null pointer exception.

 

Here, you can see my event listener for the AttachCapabilitiesEvent<Entity>, as well as the registration for my capability:

@SubscribeEvent
public static void onCommonSetup(FMLCommonSetupEvent event) {
    CapabilityManager.INSTANCE.register(ILifeForce.class, new LifeForceStorage(), LifeForce::new);
}

@SubscribeEvent
public static void onAttachCapabilities(AttachCapabilitiesEvent<Entity> event) {
    if(event.getObject() instanceof LivingEntity) {
        event.addCapability(new ResourceLocation(LifePower.MODID, "lifeforce"), new LifeForceProvider());
        event.getObject().getCapability(LifeForceProvider.LIFE_FORCE_CAP).ifPresent((capability) -> {
            capability.set(Math.round(((LivingEntity) event.getObject()).getHealth()));
        });
    }
}

 

Here's the gist of the crash report:

Description: Ticking memory connection

java.lang.NullPointerException: Ticking memory connection
	at com.networkoverflow.lifepower.content.capabilities.LifeForceProvider.<init>(LifeForceProvider.java:14) ~[classes/:?] {pl:capability_inject_definalize:A}
	at com.networkoverflow.lifepower.content.capabilities.CapabilityHandler.onAttachCapabilities(CapabilityHandler.java:25) ~[classes/:?] {}
	at net.minecraftforge.eventbus.ASMEventHandler_0_CapabilityHandler_onAttachCapabilities_AttachCapabilitiesEvent.invoke(.dynamic) ~[?:?] {}

(Full Crash Report)

 

Here is my LifeForceProvider.java (with line 14, the crash line, marked):

package com.networkoverflow.lifepower.content.capabilities;

import net.minecraft.nbt.INBT;
import net.minecraft.util.Direction;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.CapabilityInject;
import net.minecraftforge.common.capabilities.ICapabilitySerializable;
import net.minecraftforge.common.util.LazyOptional;

public class LifeForceProvider implements ICapabilitySerializable<INBT> {
    @CapabilityInject(ILifeForce.class)
    public static final Capability<ILifeForce> LIFE_FORCE_CAP = null;

    private LazyOptional<ILifeForce> instance = LazyOptional.of(LIFE_FORCE_CAP::getDefaultInstance); //THIS IS WHAT CRASHES <-----

    @Override
    public <T> LazyOptional<T> getCapability(Capability<T> capability, Direction direction) {
        return capability == LIFE_FORCE_CAP ? instance.cast() : LazyOptional.empty();
    }

    @Override
    public INBT serializeNBT() {
        return LIFE_FORCE_CAP.getStorage().writeNBT(LIFE_FORCE_CAP, this.instance.orElseThrow(() -> new IllegalArgumentException("LazyOptional must not be empty!")), null);
    }

    @Override
    public void deserializeNBT(INBT nbt) {
        LIFE_FORCE_CAP.getStorage().readNBT(LIFE_FORCE_CAP, this.instance.orElseThrow(() -> new IllegalArgumentException("LazyOptional must not be empty!")), null, nbt);
    }
}

 

So, as you can see, the LazyOptional.of() that I'm calling is raising a NullPointerException, which I think refers to LIFE_FORCE_CAP being null. However, I thought that because that variable has the @CapabilityInject annotation, its null value would be replaced with whatever forge generates.

 

One reason I could think of for this happening is if I'm hooking into the wrong place to register my capability. In this thread, @Animefan8888 mentioned that the call to CapabilityManager.INSTANCE.register() should happen in the FMLCommonSetupEvent. Is this the wrong place to register my capability, or am I doing something else wrong?

 

All code related to this capability

Edited January 19, 20205 yr by AnZaNaMa

You have told it to call a method called "getDefaultInstance" but this method does not exist anywhere I can find.

LIFE_FORCE_CAP is a Capability<ILifeForce>, so the call to LIFE_FORCE_CAP::getDefaultInstance will resolve to Capability::getDefaultInstance which does exist. I was under the impression that getDefultInstance would return the instance of LifeForce that I passed into CapabilityManager.INSTANCE.register()

Your capability registered object and the capability data are not the same thing.

For example, this:

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/farming/entities/capabilities/MilkStorage.java#L28-L33

Returns a new instance of the class that holds the capability data.

 

My capability attach event:

https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/farming/FarmingEventHandler.java#L761

 

(Note: that is 1.12 code and there have been changes, but it should at least work as a template to understand what's going on)

I managed to figure it out. I had my @EventBusSubscriber wrong (had to subscribe to the client-specific bus for the FMLCommonSetupEvent). Because of that, the event handler wasn't firing, so the instance of the capability was never being injected with a value, so it was still null when I tried to use it.

 

@Draco18s also, you were right. I was just passing an instance of my ILifeForce, when I needed to pass it a supplier. I ended up using a lambda supplier:

@SubscribeEvent
public static void onCommonSetupEvent(FMLCommonSetupEvent event) {
    CapabilityManager.INSTANCE.register(ILifeForce.class, new LifeForceStorage(), () -> new LifeForce());
}