I have a new entity, but when I log out of the world, the entity despawns and isn't there when I come back in. I'm using the latest version of forge (I think) and MC 1.4.2.

 

EntityMech.java (without the pointless parts, only the important ones I think)

package nerdicus.fwc;

import java.util.Iterator;
import java.util.List;
import java.util.UUID;

import net.minecraft.src.AxisAlignedBB;
import net.minecraft.src.Block;
import net.minecraft.src.DamageSource;
import net.minecraft.src.Entity;
import net.minecraft.src.EntityBoat;
import net.minecraft.src.EntityPlayer;
import net.minecraft.src.EntityTracker;
import net.minecraft.src.Item;
import net.minecraft.src.Material;
import net.minecraft.src.MathHelper;
import net.minecraft.src.NBTTagCompound;
import net.minecraft.src.NBTTagDouble;
import net.minecraft.src.NBTTagFloat;
import net.minecraft.src.NBTTagList;
import net.minecraft.src.World;
import cpw.mods.fml.common.Side;
import cpw.mods.fml.common.asm.SideOnly;

public class EntityMech extends Entity
{
    private boolean field_70279_a;
    private double field_70276_b;
    private int mechPosRotationIncrements;
    private double mechX;
    private double mechY;
    private double mechZ;
    private double mechYaw;
    private double mechPitch;
    @SideOnly(Side.CLIENT)
    private double velocityX;
    @SideOnly(Side.CLIENT)
    private double velocityY;
    @SideOnly(Side.CLIENT)
    private double velocityZ;

    public EntityMech(World par1World)
    {
        super(par1World);
        this.field_70279_a = true;
        this.field_70276_b = 0.07D;
        this.preventEntitySpawning = true;
        this.setSize(1.5F, 0.6F);
        this.yOffset = this.height / 2.0F;
    }
protected void writeEntityToNBT(NBTTagCompound par1NBTTagCompound)
    {
    	par1NBTTagCompound.setTag("Pos", this.newDoubleNBTList(new double[] {this.posX, this.posY + (double)this.ySize, this.posZ}));
        par1NBTTagCompound.setTag("Motion", this.newDoubleNBTList(new double[] {this.motionX, this.motionY, this.motionZ}));
        par1NBTTagCompound.setTag("Rotation", this.newFloatNBTList(new float[] {this.rotationYaw, this.rotationPitch}));
        par1NBTTagCompound.setFloat("FallDistance", this.fallDistance);
        //par1NBTTagCompound.setShort("Fire", (short)this.fire);
        par1NBTTagCompound.setShort("Air", (short)this.getAir());
        par1NBTTagCompound.setBoolean("OnGround", this.onGround);
        par1NBTTagCompound.setInteger("Dimension", this.dimension);
        //if (persistentID != null)
        //{
        //    par1NBTTagCompound.setLong("PersistentIDMSB", persistentID.getMostSignificantBits());
        //    par1NBTTagCompound.setLong("PersistentIDLSB", persistentID.getLeastSignificantBits());
        //}
        //if (customEntityData != null)
        //{
        //    par1NBTTagCompound.setCompoundTag("ForgeData", customEntityData);
        //}
        this.writeEntityToNBT(par1NBTTagCompound);
    }

    /**
     * (abstract) Protected helper method to read subclass entity data from NBT.
     */
    protected void readEntityFromNBT(NBTTagCompound par1NBTTagCompound)
    {
    	NBTTagList var2 = par1NBTTagCompound.getTagList("Pos");
        NBTTagList var3 = par1NBTTagCompound.getTagList("Motion");
        NBTTagList var4 = par1NBTTagCompound.getTagList("Rotation");
        this.motionX = ((NBTTagDouble)var3.tagAt(0)).data;
        this.motionY = ((NBTTagDouble)var3.tagAt(1)).data;
        this.motionZ = ((NBTTagDouble)var3.tagAt(2)).data;

        if (Math.abs(this.motionX) > 10.0D)
        {
            this.motionX = 0.0D;
        }

        if (Math.abs(this.motionY) > 10.0D)
        {
            this.motionY = 0.0D;
        }

        if (Math.abs(this.motionZ) > 10.0D)
        {
            this.motionZ = 0.0D;
        }

        this.prevPosX = this.lastTickPosX = this.posX = ((NBTTagDouble)var2.tagAt(0)).data;
        this.prevPosY = this.lastTickPosY = this.posY = ((NBTTagDouble)var2.tagAt(1)).data;
        this.prevPosZ = this.lastTickPosZ = this.posZ = ((NBTTagDouble)var2.tagAt(2)).data;
        this.prevRotationYaw = this.rotationYaw = ((NBTTagFloat)var4.tagAt(0)).data;
        this.prevRotationPitch = this.rotationPitch = ((NBTTagFloat)var4.tagAt(1)).data;
        this.fallDistance = par1NBTTagCompound.getFloat("FallDistance");
        //this.fire = par1NBTTagCompound.getShort("Fire");
        this.setAir(par1NBTTagCompound.getShort("Air"));
        this.onGround = par1NBTTagCompound.getBoolean("OnGround");
        this.dimension = par1NBTTagCompound.getInteger("Dimension");
        this.setPosition(this.posX, this.posY, this.posZ);
        this.setRotation(this.rotationYaw, this.rotationPitch);
        //if (par1NBTTagCompound.hasKey("ForgeData"))
        //{
        //    customEntityData = par1NBTTagCompound.getCompoundTag("ForgeData");
        //}
        //if (par1NBTTagCompound.hasKey("PersistentIDMSB") && par1NBTTagCompound.hasKey("PersistentIDLSB"))
        //{
        //    persistentID = new UUID(par1NBTTagCompound.getLong("PersistentIDMSB"), par1NBTTagCompound.getLong("PersistentIDLSB"));
        //}
        this.readEntityFromNBT(par1NBTTagCompound);
    }

  Sorry about indentation issues

 

FutureWarCraft.java

package nerdicus.fwc; //Change this to your package

import net.minecraft.src.Block;
import net.minecraft.src.EnumCreatureType;
import net.minecraft.src.FurnaceRecipes;
import net.minecraft.src.Item;
import net.minecraft.src.ItemStack;
import net.minecraft.src.ModLoader;
import cpw.mods.fml.common.Mod;
import cpw.mods.fml.common.Mod.Init;
import cpw.mods.fml.common.Mod.Instance;
import cpw.mods.fml.common.event.FMLInitializationEvent;
import cpw.mods.fml.common.network.NetworkMod;
import cpw.mods.fml.common.registry.EntityRegistry;
import cpw.mods.fml.common.registry.GameRegistry;
import cpw.mods.fml.common.registry.LanguageRegistry;

@NetworkMod(clientSideRequired=true, serverSideRequired=false)
@Mod(modid="FWC", name="Future Warcraft", version="Alpha v0.1")

public class FutureWarCraft
{
@Instance
public FutureWarCraft instance;

@Init
public void FWCInit(FMLInitializationEvent initEvent)
{
	EntityRegistry.registerModEntity(EntityMech.class, "FWCMech", EntityRegistry.findGlobalUniqueEntityId(), instance, 50, 50, true);
}

Again, sorry about any possible issues.

 

Any ideas? The entity spawns fine, but it just doesn't save itself. I just copied the boat code and modified it a little bit, but it's not working.

 

If you need any more of the code, I'd be glad to supply it. I've had this problem for about 1.5 months.

Try changing the read and write methods in the entity to public

Nope, it still doesn't work. Thanks anyways though!

This happened to me! I solved it by using the proxys system, look for it here:http://wuppy29.blogspot.nl/2012/10/forge-modding-142.html