I'm trying to make it so that my GUI slot can only accept certain items. I have created a new class, extended Slot and overwritten isItemValid() to try and do this, however I'm sorta stuck on how to actually set up a filter. My code (below) crashes the game on the line inside the first for loop with a nullPointerException. Any help would be appriciated. Thanks.

 

Code:

package roboguy99.foodTech.client.gui;

import net.minecraft.inventory.IInventory;
import net.minecraft.inventory.Slot;
import net.minecraft.item.ItemStack;

public class FilteredSlot extends Slot
{
private ItemStack[] allowedItems;
private boolean[] filterResponses;

public FilteredSlot(IInventory inventory, int id, int x, int y, ItemStack[] allowedItems)
{
	super(inventory, id, x, y);
	this.allowedItems = allowedItems;
}

@Override
public boolean isItemValid(ItemStack itemstack)
{
	this.filterResponses = new boolean[this.allowedItems.length];

	if(this.allowedItems != null)
	{
		for(int i = 0; i < this.allowedItems.length; i++)
		{
			this.filterResponses[i] = this.allowedItems[i] == itemstack ? true : false;
		}
	}

	if(this.filterResponses != null)
	{
		for(int i = 0; i < this.filterResponses.length; i++)
		{
			if (this.filterResponses[i] == true) return true;
		}
	}

	return false;
}
}

That is not how you compare ItemStacks.  ItemStack is a complex data class and you need to check for equality in a different way.  The == operator tells you if the two variables reference the same object in memory.

That is not how you compare ItemStacks.  ItemStack is a complex data class and you need to check for equality in a different way.  The == operator tells you if the two variables reference the same object in memory.

 

Would I use the getItem() function or use .equals() or something else please?

I know that the smelting recipes uses getItem and getItemDamage (remember: metadata is important!).  You would have to look at equals so see what it does.  There's also a version of equation that checks NBT data.

Hmm ok. I suppose it would make sense to have a look at the code for the furnace container and see how it does that then. I'll have a look and come back here if I need any more help.

One thing to note with getItemDamage() is tools or other damageable items, in those cases I'd say you'd have to check getHasSubtypes() aswell to see if there are other types of blocks/items on the same id. (One alternative is to call isDamageable() on the item, they are almost the same)

Here's the code I borrowed from the smelting recipe registry when making my own machine.

 

private static boolean areSame(ItemStack input, ItemStack against) {
	if(input == null || against == null) return false;
        return against.getItem() == input.getItem() && (against.getItemDamage() == 32767 || against.getItemDamage() == input.getItemDamage());
    }

 

"against" is the stored itemstack that the slot item is compared against.

You might want to replace the hardcoded wildcard value with

OreDicitionary.WILDCARD_VALUE

for future compatibility.

 

Good point.  Again, it was just what I'd yoinked from the recipe manager.  My mod, while I will likely release it, is primarily intended to scratch my own itches.

Ok this looks good, thanks. I haven't had a chance yet but I'll try and get this working.

Also, don't store these in your Slot class (you'd be duplicating your efforts, if the TE also stores the same info).  Make a static "RecipeManager" class that has a "getResult" method.  Your slot class just needs to then go "hey, does this input have a non-null result?" for it's boolean check.  Then your machine can use the same function to get its actual result.