I need to loop through a list in an event handler (specifically for the HarvestDropsEvent), but when I use a for loop it throws a ticking world exception. Is there an accepted way of looping in event handlers?

Show what you tried.

@SubscribeEvent
	public void blockBreak(HarvestDropsEvent event)
	{
		World world = event.getWorld();
		if(!world.isRemote)
		{
			ForageTable table = ForageCraftMod.ForageDict.get(event.getState().getBlock());
			
			java.util.List<ForagePool> pools = table.getPools();
			
			for(int i = 0; i != pools.size(); i++)
			{
				ForagePool pool = table.getPool(i);
				
				if(CHANCE.nextFloat()<pool.getChance())
				{
					event.getDrops().add(new ItemStack(ForgeRegistries.ITEMS.getValue(new ResourceLocation(pool.getItem())), pool.getAmount()));
				}
			}
		}
	}

ForageDict is a hashtable using blocks as keys and returning a foragetable object. foragetables are containers for lists of foragepools, which hold a set of primitive values for use in this code, which adds new drops to blocks via json files.

Also, heres the crash log, if it helps:

 

Pastebin Link

Quote

Caused by: java.lang.NullPointerException

Its on line 31, whichever line that is.

4 minutes ago, Draco18s said:

Its on line 31, whichever line that is.

Don't you mean 33?

Quote

Caused by: java.lang.NullPointerException

    at com.theishiopian.foragecraft.handler.BlockForageHandler.blockBreak(BlockForageHandler.java:33)

 

Line 33 is the for loop.

Then table.getPools(); returned null and you didn't check for that.

It seems you are  right, just calling table.getPools(); crashes the game. Whats perplexing is its just a simple return function.

 

public List<ForagePool> getPools()
	{
		
		
		return this.table;
	}

this.table is a list of foragetables.

SO, for clarification, are there no problems with using for loops in event handlers?

5 minutes ago, theishiopian said:

this.table

Which must never be instantiated into an instance.

1 minute ago, theishiopian said:

SO, for clarification, are there no problems with using for loops in event handlers?

No there isn't. 

Ok, good to know. For some reason, my list is becoming null. The weird thing is that I can call from it elsewhere and get the correct result. Anyways, thanks for the clarification, that really helps narrow it down.

 

 

Also, what did you mean by "instantiated into an instance"? Do you mean initilized as an object? If so, I'm already doing that.

 

ForageTable table = ForageCraftMod.ForageDict.get(event.getState().getBlock());

 

Ok, this is very bizzare. Whenever I try to reference my hashtable, I get a null pointer exception. But whenever I do a null check on it, it returns false.

A tip for combatting NPEs is to make everything that possibly can be final final. Then the compiler will let you know if you forgot to initialise your field.

Step through your code with the debugger and find out why it’s null

Thanks for the tip. Im going to massively refactor this tomorrow. Ill also step through it with the debugger. I think it has to do with the way im creating the forage pools from json. Which is odd because it worked before. If i have any more issues tommorow, ill create a new thread. Night all.

27 minutes ago, theishiopian said:

Also, what did you mean by "instantiated into an instance"? Do you mean initilized as an object? If so, I'm already doing that.

 

ForageTable table = ForageCraftMod.ForageDict.get(event.getState().getBlock());

 

What if that block doesnt have a ForageTable? Also why are you using a Block and not a IBlockState for your key.

I know it has a foragetable. I think the foragetables are getting set to null somewhere.

 

I hadnt considered using blockstates. Do they have a string representation like blocks do? (eg minecraft:dirt)

18 minutes ago, theishiopian said:

I hadnt considered using blockstates. Do they have a string representation like blocks do? (eg minecraft:dirt)

Not an explicit one. It would first specify the Block I'd "minecraft:dirt" and then it would specify the property name and then the value, both can be represented by strings.

Huh, ill probably do that once i get it working with just blocks. 

9 hours ago, theishiopian said:

Do they have a string representation like blocks do? (eg minecraft:dirt)

Its almost as if you've not actually played the game.

1) The F3 screen

2) The /give command

3) Blockstate JSON files (and the associated error messages when they aren't correct)

 

All three of these use string representations of blockstates.

 

Or there's just the sheer point that: anything can be turned into a string if you try hard enough.