I want to be able to add a capability to an "existing" item stack. The reason not to apply this capability to all item stacks is because I'm going to be tracking a pretty hefty chunk of data and I don't want to attach that to everything, just the stacks that need it (applied via a machine), and narrowing by item type doesn't help much, as I'm going to want to apply this to a wide variety of item types.

 

Is there a way to do this?

 

If not, I may have to fall back to storing the data in its serialized format in the stack's NBT instead, which is not ideal, but workable.

2 hours ago, diesieben07 said:

Just like with other capability providers (like tile entities), you can subscribe to AttachCapabilitiesEvent<ItemStack>.

did you read what Draco18s wrote ??

 

what you can do is

add a cap using the event  that allows adding/removing caps on the fly

I think you could probably just do some queries on the stack in question & decide if you want to add the capability or not. If you can't do that I think thats something that forge should definitely provide

package loordgek.itemhandlerv2.captest;

import net.minecraft.init.Items;
import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraftforge.event.AttachCapabilitiesEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

public class lol {
    public static boolean somthing = false;

    public ItemStack createNewStack(){
        somthing = true;
        ItemStack stack = new ItemStack(Items.ITEM_FRAME);
        if (!stack.hasTagCompound())
            stack.setTagCompound(new NBTTagCompound());

        stack.getTagCompound().setBoolean("somthing", true);

        somthing = false;
        return stack;
    }

    //note you should a bool to the rhe nbt of the sack if you want the cap to survive between saves
    @SubscribeEvent
    public void onAttachCapabilities(AttachCapabilitiesEvent<ItemStack> event) {
        if (event.getObject().hasTagCompound()){
            if (event.getObject().getTagCompound().hasKey("somthing"))
            //add a cap here
        }
        if (somthing)// i made the stack
        {

            //add a cap here
        }
    }
}

 

1 hour ago, loordgek said:

    @SubscribeEvent
    public void onAttachCapabilities(AttachCapabilitiesEvent<ItemStack> event) {
        if (event.getObject().hasTagCompound()){
            if (event.getObject().getTagCompound().hasKey("somthing"))
            //add a cap here
        }

 

That won't work. The event is called when new is called, and when item stacks are new, they don't have a tag.

1 hour ago, diesieben07 said:

Just adding an empty capability to every stack is fine, you can then add the data to that empty cap whenever you need, later. All stacks will have the empty cap, but only when needed you add the "hefty data".

Alright.