[1.15.1] capability NullPointerException

[transfarmer]

Hello. I made a custom capability that should be attached to EntityPlayer. My provider class initializes an instance of Capabilty and sets its value to null and makes a LazyOptional instance of this capability:

    public static final Capability<ISoulWeapon> TYPE = null;
    private LazyOptional<ISoulWeapon> instance = LazyOptional.of(TYPE::getDefaultInstance);

I assume that this is correct because this is the only way in which I saw this done. However, the instance seems to be null. The game runs until a world is loaded, when it crashes, producing the following stacktrace:

java.lang.NullPointerException: Saving entity NBT
	at transfarmer.adventureitems.capabilities.Storage.writeNBT(Storage.java:14) ~[?:?] {re:classloading}
	at transfarmer.adventureitems.capabilities.Storage.writeNBT(Storage.java:10) ~[?:?] {re:classloading}
	at transfarmer.adventureitems.capabilities.Provider.serializeNBT(Provider.java:23) ~[?:?] {re:classloading,pl:capability_inject_definalize:A}
	at net.minecraftforge.common.capabilities.CapabilityDispatcher.serializeNBT(CapabilityDispatcher.java:127) ~[?:?] {re:classloading}
	at net.minecraftforge.common.capabilities.CapabilityProvider.serializeCaps(CapabilityProvider.java:86) ~[?:?] {re:classloading}
	at net.minecraft.entity.Entity.writeWithoutTypeId(Entity.java:1527) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.server.integrated.IntegratedPlayerList.writePlayerData(IntegratedPlayerList.java:27) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.server.management.PlayerList.saveAllPlayerData(PlayerList.java:631) ~[?:?] {re:classloading}
	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:112) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:658) ~[?:?] {re:classloading,pl:accesstransformer:B}
	at java.lang.Thread.run(Thread.java:748) ~[?:1.8.0_232] {}

What did I do wrong?

My capability is available here.

[Draco18s]

Well, you set it to null and made it final. It can't be anything else (unless you apply the @ObjectHolder annotation or use reflection).

[transfarmer]

I read again the Forge documentation about capabilities. According to the it, the capability is null because it was not registered. Then I made it non-final and tried to properly register it during common setup. The NullPointerException does not occur anymore. However, my keybinding does not load anymore (I set its registration to occur during client setup by FMLClientSetupEvent as I was cleaning up my mod setup). Previously, it loaded but did not function. (It functioned as expected before I implemented the capability.) Should I open a new thread for that?

Also, the 1.15.x documentation mentions a provider hasCapability method. Is that a requirement in previous versions of Forge? It is not defined in ICapabilityProvider.java in v30.0.36.

Edited January 14, 2020 by transfarmer

[Draco18s]

  On 1/14/2020 at 11:49 PM, transfarmer said:

Is that a requirement in previous versions of Forge?

Expand  

Yes. getCapability is pretty much the only thing that interface provides.

[transfarmer]

The Forge documentation states the following:

  Quote

The return type of getCapability will correspond to the type declared in the capability passed to the method. For the Item Handler capability, this is indeed IItemHandler.

Expand  

However, the return type of getCapability is LazyOptional<T>, and I want to use the methods defined in my interface. How should I use getCapability?

[Draco18s]

Yes. It should be LazyOptional<T>. Note that <T> here is still the type of the capability, so you'll get back a LazyOptional<IItemHandler>. Which you can then call ifPresent() on and pass in a lambda that gets executed if the capability is indeed present (non-null) or you can do something like OrElse(null) and null check (prefer using ifPresent) or use OrElseThrow().

[transfarmer]

Is the capability non-null when it is registered and attached? Otherwise, how can I make it non-null? My PlayerEntity seems to not have it.

[Draco18s]

You need to attach capabilities to things you don't control. Like the player. Use the EntityJoinedWorldEvent for that.

[Draco18s]

  On 1/15/2020 at 9:47 AM, diesieben07 said:

AttachCapabilitiesEvent

Expand  

I could not remember if this was actually a thing.

[transfarmer]

I already have it:

@EventBusSubscriber(modid = Main.MODID, bus = EventBusSubscriber.Bus.MOD)
public class ModEventSubscriber {
    . . .
    @SubscribeEvent
    public static void onAttachCapabilities(AttachCapabilitiesEvent<Entity> event) {
        if (event.getObject() instanceof PlayerEntity) {
            event.addCapability(new ResourceLocation(Main.MODID, "type"), new Provider());
        }
    }
    . . .
}

Is something wrong with this code?

Edited January 15, 2020 by transfarmer

[loordgek]

you subscribe to the wrong bus remove

, bus = EventBusSubscriber.Bus.MOD

[transfarmer]

Loading a world produces a NullPointerExceptionagain. The ICapability instance passed to writeNBT seems to be null:

  Reveal hidden contents

java.lang.NullPointerException: Saving entity NBT
    at transfarmer.adventureitems.capability.SoulWeaponStorage.writeNBT(SoulWeaponStorage.java:14) ~[?:?] {re:classloading}
    at transfarmer.adventureitems.capability.SoulWeaponStorage.writeNBT(SoulWeaponStorage.java:10) ~[?:?] {re:classloading}
    at transfarmer.adventureitems.capability.SoulWeaponProvider.serializeNBT(SoulWeaponProvider.java:26) ~[?:?] {re:classloading}
    at net.minecraftforge.common.capabilities.CapabilityDispatcher.serializeNBT(CapabilityDispatcher.java:127) ~[?:?] {re:classloading}
    at net.minecraftforge.common.capabilities.CapabilityProvider.serializeCaps(CapabilityProvider.java:86) ~[?:?] {re:classloading}
    at net.minecraft.entity.Entity.writeWithoutTypeId(Entity.java:1358) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.integrated.IntegratedPlayerList.writePlayerData(SourceFile:24) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.management.PlayerList.saveAllPlayerData(PlayerList.java:602) ~[?:?] {re:classloading}
    at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:106) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:634) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:748) ~[?:1.8.0_232] {}

 

  Reveal hidden contents

public class SoulWeaponStorage implements IStorage<ISoulWeapon> {
    @Override
    public INBT writeNBT(Capability<ISoulWeapon> capability, ISoulWeapon instance, Direction side) {
        CompoundNBT tag = new CompoundNBT();
        tag.putString("adventureitems.weaponType", instance.getCurrentType().getName());
        return tag;
    }
    . . .
}

public class SoulWeaponProvider implements ICapabilitySerializable<INBT> {
    @CapabilityInject(ISoulWeapon.class)
    public static Capability<ISoulWeapon> TYPE;
    private LazyOptional<ISoulWeapon> instance = LazyOptional.of(TYPE::getDefaultInstance);
    . . .
}

 

Edited January 15, 2020 by transfarmer

[transfarmer]

  On 1/15/2020 at 8:53 PM, diesieben07 said:

Why have you not shown this?

Expand  

I apologize. The issue with writeNBT was that I was trying to use Object.toString() on a value that was null.The provider class is shown below.

  Reveal hidden contents

public class SoulWeaponProvider implements ICapabilitySerializable<INBT> {
    @CapabilityInject(ISoulWeapon.class)
    public static Capability<ISoulWeapon> TYPE;
    private LazyOptional<ISoulWeapon> instance = LazyOptional.of(TYPE::getDefaultInstance);

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

    @Override
    public INBT serializeNBT() {
        return TYPE.getStorage().writeNBT(TYPE, instance.orElseThrow(() -> new IllegalArgumentException("LazyOptional is empty")), null);
    }

    @Override
    public void deserializeNBT(INBT nbt) {
        TYPE.getStorage().readNBT(TYPE, instance.orElseThrow(() -> new IllegalArgumentException("LazyOptional is empty")), null, nbt);
    }
}

 

 

  On 1/15/2020 at 8:53 PM, diesieben07 said:

This makes no sense.

Expand  

I agree. Does it have to be initialized? If so, then what should it be?

[transfarmer]

  On 1/15/2020 at 9:07 PM, diesieben07 said:

So your issue is fixed?

Expand  

Yes.

 

  On 1/15/2020 at 9:07 PM, diesieben07 said:

I misread, for some reason I read this to be in your storage class. Your code is fine.

Expand  

Then could you explain to me what it does? I'm still not sure about why I need it. Is it a basic instance made for every object to which the capability is attached for NBT storage? Also, I think that my data are not saved after leaving and joining a world. Do I have to do it manually?