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[SOLVED] 1.16.5 - setBlock() usage from my custom Item.use() override makes only temporary changes to the world

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I was asked to make a separate thread for this instead of tacking on to another setBlock() question, so here goes.

I'm just testing out trying to modify the world with setBlock(), and it's just not behaving like I'd expect.  

The other question answered my own questions about the integer parameters for setBlock(), so I'm now passing in Constants.BlockFlags.DEFAULT.  This really is just like the behavior of the setBlockAndUpdate() method anyway.... which I was trying at one point.

The behavior I'm seeing is that the blocks appear in the world, but disappear when interacting with them and the previous blocks (if any) reappear.  All of these blocks are reverted and are not saved if I quit to title and restart the world.  I can climb on them and bump off of them, but that's about it.

This is launching from the Forge MDK runClient configuration.  (Edit: specifically, forge-1.16.5-36.1.4-mdk via IntelliJ IDEA)

Most people's questions about setBlock() seem quite straightforward and like it just works for them.

It's almost like a problem passing in immediate variables that get deleted when they go out of scope ... but the few examples I find are using defaultBlockState() and aren't calling new or anything... ?

I can use the ModBlocks.MYBLOCK blocks normally within the game otherwise... as in, place them as in game blocks from creative/survival mode, etc.. they only misbehave from the Item.use() override...

Other changes to the current chunk made after inserting these blocks from normal creative/survival game interactions are saved.


package com.mydomain.testmod;

import net.minecraft.block.Block;
import net.minecraft.block.BlockState;
import net.minecraft.command.arguments.BlockStateArgument;
import net.minecraft.entity.player.PlayerEntity;
import net.minecraft.inventory.EquipmentSlotType;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.util.ActionResult;
import net.minecraft.util.ActionResultType;
import net.minecraft.util.Hand;
import net.minecraft.util.math.BlockPos;
import net.minecraft.world.World;
import net.minecraft.world.chunk.Chunk;
import net.minecraftforge.common.util.Constants;

public class ItemTest extends Item {

    public ItemTest(Properties prop) {

    public ActionResult<ItemStack> use(World world, PlayerEntity player, Hand hand) {
        if (world.isClientSide)
            if (hand == Hand.MAIN_HAND)
                BlockPos pos = new BlockPos(player.position());// RayTraceUtil.getTargetBlockPos(player, world, 25);
                Block targetBlock = ModBlocks.MYBLOCK.get();

                if(pos != null) {
                    for (int y = 0; y < 10; y++) {
                        for (int i = -5; i <= 5; i++) {
                            if ((i != 0) || (y > 1)) {
                                world.setBlock(pos.offset(5, y, i), targetBlock.defaultBlockState(), Constants.BlockFlags.DEFAULT);

                            world.setBlock(pos.offset(i, y, 5), targetBlock.defaultBlockState(), Constants.BlockFlags.DEFAULT);
                            world.setBlock(pos.offset(-5, y, i), targetBlock.defaultBlockState(), Constants.BlockFlags.DEFAULT);
                            world.setBlock(pos.offset(i, y, -5), targetBlock.defaultBlockState(), Constants.BlockFlags.DEFAULT);

                    return ActionResult.pass(player.getItemInHand(hand));

        return super.use(world, player, hand);

The item is registered like so:

public class ModItems {
    public static final DeferredRegister<Item> ITEMS = DeferredRegister.create(ForgeRegistries.ITEMS, TestMod.MODID);

    public static final RegistryObject<Item> ITEMTEST = ITEMS.register("itemtest", () -> new ItemTest(new Item.Properties().tab(ItemGroup.TAB_MISC)));

    public static void init() {

... and the block:

public class ModBlocks {
	public static final DeferredRegister<Block> BLOCKS = DeferredRegister.create(ForgeRegistries.BLOCKS, TestMod.MODID);
    public static final RegistryObject<Block> MYBLOCK = register("myblock", () -> new Block(AbstractBlock.Properties.of(Material.STONE).requiresCorrectToolForDrops().sound(SoundType.STONE)));

    static void init() {

    private static <T extends Block> RegistryObject<T> registerNoItem(String name, Supplier<T> block) {
    	return BLOCKS.register(name, block);

    private static <T extends Block> RegistryObject<T> register(String name, Supplier<T> block) {
    	RegistryObject<T>  ret = registerNoItem(name, block);
    	ModItems.ITEMS.register(name, () -> new BlockItem(ret.get(), new Item.Properties().tab(ItemGroup.TAB_BUILDING_BLOCKS)));
    	return ret;


Usually, I'd have made my own thread from the start... but the other thread basically was answering my main question already (setBlock integer parameter usage), so...  :)

Edited by wintermaker
is this how you mark solved?
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3 minutes ago, ChampionAsh5357 said:

You messed up your check. You're only supposed to execute when not on the client.

Ok... I knew that was a potential issue when running on a server... but I thought in single player mode there was only the client anyway.  (I'm pretty new)

So... apparently this is running twice, from both the client and a local server instance that's just not listening for external connections?  Obviously so... as something happened in both conditions.

I mean, it makes sense.  I'm not sure why I didn't try that.  Thanks!

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  • wintermaker changed the title to [SOLVED] 1.16.5 - setBlock() usage from my custom Item.use() override makes only temporary changes to the world
2 hours ago, wintermaker said:

Ok... I knew that was a potential issue when running on a server... but I thought in single player mode there was only the client anyway.

This was the case prior to Minecraft 1.3, single player was a completely separate system. In 1.3 this was ditched in favor of running an integrated server to simplify the code and provide more stability as well as things like "Open to LAN".

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