Hey everyone, I'm trying to do when player eat custom food he gains a custom effect that makes player can't swim. 
I created a custom effect like this ;

public class cantSwimEffect extends MobEffect {

    public cantSwimEffect(MobEffectCategory mobEffectCategory, int color) {
        super(mobEffectCategory, color);
    }

    @Override
    public void applyEffectTick(LivingEntity pLivingEntity, int pAmplifier) {

        if (!pLivingEntity.level().isClientSide() && pLivingEntity.isInWater()) {

            pLivingEntity.addEffect(new MobEffectInstance(MobEffects.MOVEMENT_SLOWDOWN,400));

        };


    }

    @Override
    public  boolean isDurationEffectTick(int pDuration, int pAmplifier) {
        return true;
    }
}

I created a custom food like this ;
 

public class ModFoods {

    public static final FoodProperties custom_food = new FoodProperties.Builder().nutrition(2).saturationMod(02.f).fast().build();


}

But I don't know how to add that custom effect to this food ? Can anyone help me ?

Use FoodProperties.Builder#effect which takes a MobEffectInstance Supplier and the chance of the effect (0.0 - 1.0)

I would recommend to follow the java naming convention.

2 hours ago, Luis_ST said:

Use FoodProperties.Builder#effect which takes a MobEffectInstance Supplier and the chance of the effect (0.0 - 1.0)

I would recommend to follow the java naming convention.

Thank you for your answer ! I did something like that ; 

public static final FoodProperties MERA_MERA_NO_MI = new FoodProperties.Builder().nutrition(2).fast()
            .saturationMod(0.2f).effect(() -> new MobEffectInstance(new CantSwimEffect(MobEffectCategory.HARMFUL,4866583)),1).build();

But in game I can only eat that food when I'm in creative mod. And also after I ate that java occurs this error ;

java.lang.IllegalArgumentException: No delegate exists for value net.mbkgr.opmod.item.custom.customeffect.cantSwimEffect@44b4927a

What is the problem can you help me ?

Please post ful log.

The error uses cantSwimEffect but in your code you use CantSwimEffect, make sure this is not the problem.

Time: 2023-11-11 22:40:00
Description: Ticking player

java.lang.IllegalArgumentException: No delegate exists for value net.mbkgr.opmod.item.custom.customeffect.CantSwimEffect@2d3e42e0
    at net.minecraftforge.registries.ForgeRegistry.lambda$getDelegateOrThrow$5(ForgeRegistry.java:542) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23190%23197!/:?] {re:classloading}
    at java.util.Optional.orElseThrow(Optional.java:403) ~[?:?] {}
    at net.minecraftforge.registries.ForgeRegistry.getDelegateOrThrow(ForgeRegistry.java:542) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23190%23197!/:?] {re:classloading}
    at net.minecraft.world.effect.MobEffectInstance.getEffect(MobEffectInstance.java:145) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:potion}
    at net.minecraft.world.effect.MobEffectInstance.<init>(MobEffectInstance.java:64) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:potion}
    at net.minecraft.world.entity.LivingEntity.addEatEffect(LivingEntity.java:3504) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.LivingEntity.eat(LivingEntity.java:3488) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.player.Player.eat(Player.java:2153) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.item.Item.finishUsingItem(Item.java:168) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.item.ItemStack.finishUsingItem(ItemStack.java:293) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:itemstack}
    at net.minecraft.world.entity.LivingEntity.completeUsingItem(LivingEntity.java:3213) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.level.ServerPlayer.completeUsingItem(ServerPlayer.java:1162) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.entity.LivingEntity.updateUsingItem(LivingEntity.java:3092) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.level.ServerPlayer.updateUsingItem(ServerPlayer.java:1766) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.entity.LivingEntity.updatingUsingItem(LivingEntity.java:3074) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.LivingEntity.tick(LivingEntity.java:2402) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.player.Player.tick(Player.java:245) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.level.ServerPlayer.doTick(ServerPlayer.java:489) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.network.ServerGamePacketListenerImpl.tick(ServerGamePacketListenerImpl.java:267) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.network.Connection.tick(Connection.java:289) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.network.ServerConnectionListener.tick(ServerConnectionListener.java:159) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:937) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:844) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.client.server.IntegratedServer.tickServer(IntegratedServer.java:95) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:679) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:251) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:840) ~[?:?] {}


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Server thread
Stacktrace:
    at net.minecraftforge.registries.ForgeRegistry.lambda$getDelegateOrThrow$5(ForgeRegistry.java:542) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23190%23197!/:?] {re:classloading}
    at java.util.Optional.orElseThrow(Optional.java:403) ~[?:?] {}
    at net.minecraftforge.registries.ForgeRegistry.getDelegateOrThrow(ForgeRegistry.java:542) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23190%23197!/:?] {re:classloading}
    at net.minecraft.world.effect.MobEffectInstance.getEffect(MobEffectInstance.java:145) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:potion}
    at net.minecraft.world.effect.MobEffectInstance.<init>(MobEffectInstance.java:64) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:potion}
    at net.minecraft.world.entity.LivingEntity.addEatEffect(LivingEntity.java:3504) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.LivingEntity.eat(LivingEntity.java:3488) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.player.Player.eat(Player.java:2153) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.item.Item.finishUsingItem(Item.java:168) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.item.ItemStack.finishUsingItem(ItemStack.java:293) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,xf:fml:forge:itemstack}
    at net.minecraft.world.entity.LivingEntity.completeUsingItem(LivingEntity.java:3213) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.level.ServerPlayer.completeUsingItem(ServerPlayer.java:1162) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.entity.LivingEntity.updateUsingItem(LivingEntity.java:3092) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.level.ServerPlayer.updateUsingItem(ServerPlayer.java:1766) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.entity.LivingEntity.updatingUsingItem(LivingEntity.java:3074) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.LivingEntity.tick(LivingEntity.java:2402) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.world.entity.player.Player.tick(Player.java:245) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
-- Player being ticked --
Details:
    Entity Type: minecraft:player (net.minecraft.server.level.ServerPlayer)
    Entity ID: 231
    Entity Name: Dev
    Entity's Exact location: 7.55, 123.00, 10.53
    Entity's Block location: World: (7,123,10), Section: (at 7,11,10 in 0,7,0; chunk contains blocks 0,-64,0 to 15,319,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,-64,0 to 511,319,511)
    Entity's Momentum: 0.00, -0.08, 0.00
    Entity's Passengers: []
    Entity's Vehicle: null
Stacktrace:
    at net.minecraft.server.level.ServerPlayer.doTick(ServerPlayer.java:489) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.network.ServerGamePacketListenerImpl.tick(ServerGamePacketListenerImpl.java:267) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.network.Connection.tick(Connection.java:289) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.network.ServerConnectionListener.tick(ServerConnectionListener.java:159) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading}
    at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:937) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:844) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.client.server.IntegratedServer.tickServer(IntegratedServer.java:95) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:679) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:251) ~[forge-1.20.1-47.2.1_mapped_parchment_2023.06.26-1.20.1-recomp.jar%23191!/:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:840) ~[?:?] {}

That is the full crash report. And yes I checked it it's correct.

Your MobEffect (CantSwimEffect) is a registry object, you must not create a new instance of it you should use the one your registered.

38 minutes ago, Luis_ST said:

Your MobEffect (CantSwimEffect) is a registry object, you must not create a new instance of it you should use the one your registered.

Thank you I changed it like that and solved it ;
 

public static final FoodProperties MERA_MERA_NO_MI = new FoodProperties.Builder().nutrition(2).fast() .saturationMod(0.2f).effect(() -> new MobEffectInstance(ModEffects.CANT_SWIM.get()),1).build();

But I can't eat the food while player in survival mod. Why ?

14 minutes ago, gbln00 said:

Thank you I changed it like that and solved it ;
 

public static final FoodProperties MERA_MERA_NO_MI = new FoodProperties.Builder().nutrition(2).fast() .saturationMod(0.2f).effect(() -> new MobEffectInstance(ModEffects.CANT_SWIM.get()),1).build();

But I can't eat the food while player in survival mod. Why ?

Ah sorry. I solved it . There was an registration error. Thanks for help again.