[1.15.2] Reflection to Change Item#maxStackSize

[izofar]

Item#maxStackSize is a private final int and I would like to use reflection to change this. For context, I have the following code:

 

Spoiler

public abstract class StackSizeEditor {
  
	private static Field maxStackSize;

	//Mapping of stack sizes I'd like to change
	private static HashMap<Item, Integer> stackSizes = new HashMap<Item, Integer>()
		{{
			//honey bottle item
			put(Items.field_226638_pX_, 1);
	
		}}; 
	
	public static void adjustStackSizes() {
		try {
			maxStackSize = ObfuscationReflectionHelper.findField(Item.class, "maxStackSize");
			maxStackSize.setAccessible(true);
			stackSizes.forEach(new SetField(maxStackSize));
			
		} catch (SecurityException e) {e.printStackTrace();}
		
	}
	
	private static class SetField implements BiConsumer<Item, Integer>{

		private Field field;
		
		public SetField(Field field) {
			this.field = field;
		}
		
		@Override
		public void accept(Item item, Integer integer) {
			try {
				field.set(item, integer);
			} catch (IllegalArgumentException | IllegalAccessException e) {e.printStackTrace();}
		}
		
	}
}

 

 

From this I get the following in latest.log:

Spoiler

net.minecraftforge.fml.common.ObfuscationReflectionHelper$UnableToFindFieldException: java.lang.NoSuchFieldException: maxStackSize
[12May2020 13:40:56.681] [modloading-worker-3/INFO] [STDERR/]: [com.izofar.examplemod.util.StackSizeEditor:adjustStackSizes:31]: 	
at net.minecraftforge.fml.common.ObfuscationReflectionHelper.findField(ObfuscationReflectionHelper.java:242)

 

 

From this, I believe that there have been no static references to the Item class at the point of this code being run (my error occurs on startup). This would make sense for I am calling the StackSizeEditor.adjustStackSizes() method in a static block in one of my event handlers. My question is, if the meat of the code is correct (which, I believe to be so, because ./gradlew runClient doesn't give me this error, only running from the launcher with the file as result of ./gradlew build), then where do I make the call to the above code? On world startup?

 

Another note: when I change SecurityException e to Exception e, I don't get a null error on startup (to be expected because the exception is handled), but the honey bottle item is still stackable (also to be expected if the reflection failed). This is why I suspect that I must call this method elsewhere in my code. I, however, am not sure where.

 

Edit: reformatted code-block w/ comments for readability

 

Update: I figured to move this call to the items registry method (since I figure some static reference to the Item class has happened). Sure enough, my error changed from null to NoSuchFieldException as shown in latest.log. I have indeed verified that Item#maxStackSize does exist. Once again, ./gradlew runClient works just fine and yields the desired behavior. My issue occurs on running the Minecraft launcher on my built jar (and yes, I verified that the versions of Forge being run are the same). I just came across ObfuscationHelper.setPrivateValue, so maybe I'll give that a try...

Edited May 12, 2020 by izofar

[loordgek]

what are you trying to do from a end user perspective

[izofar]

1 minute ago, loordgek said:

what are you trying to do from a end user perspective

Trying to change the maxStackSize of honey bottle to 1 (like potions/water bottles/etc.)

[izofar]

In researching reflection with Forge, I came across MCPBot and Jabelar's helpful post explaining how it works. I noticed that the latest MCPBot snapshot is for 1.15.1, does this mean I can't yet use reflection the way I intend to in 1.15.2? Jabelar also cited the event of reflection working in the IDE but not the build, which leads me to have such suspicions.

 

Such leads me to ask, because I am trying to change maxStackSize, this field was obfuscated as field_200920_a in 1.15.1 according to MCPBot. how likely is this to have changed in 1.15.2? Do they get randomly generated per every update or do they usually remain consistent? (From comparing across 1.15.1 and 1.14.4, they seem to remain the same)

Edited May 12, 2020 by izofar

[imacatlolol]

I'd recommend just replacing the registry entry for the item, not sure if using reflection is really the best option here.

In any case, ObfuscationReflectionHelper takes the unmapped SRG name, not the mapped name.

[izofar]

2 minutes ago, imacatlolol said:

I'd recommend just replacing the registry entry for the item, not sure if using reflection is really the best option here.

In any case, ObfuscationReflectionHelper takes the unmapped SRG name, not the mapped name.

Just to make sure I understand: To do this, I would copy the vanilla code to redefine the honey bottle item myself, then re-register it as minecraft:honey_bottle? Would this effect events like collecting honey from beehives (which returns the original minecraft:honey_bottle)?

[loordgek]

extend the itemclass

[imacatlolol]

Yes, that's all you need to do. It won't affect any of the game's normal behaviors, aside from what you change (i.e. the stack size).

I recommend adding an option in your mod's config to disable this feature if desired by users, but that's up to you. You may also want to use a different event priority for registering your replaced item to make it harder/easier for other mods to override your replacement by default.