Hello, I am working on something that lets me change an item's NBT when it is being crafted with (A transmutation stone).

I have this method:

    @SubscribeEvent
    public void ItemCraftedEvent(PlayerEvent.ItemCraftedEvent e)
    {
        // If the item crafted is the transmutation stone
        if (e.crafting.getItem() instanceof BasicTransmutationStone)
        {
            e.crafting.stackTagCompound = new NBTTagCompound();
            e.crafting.stackTagCompound.setString("owner", e.player.getDisplayName());
            e.crafting.stackTagCompound.setInteger("uses", 128);
            return;
        }
        // If the item being used in crafting is the transmutation stone
        for (int i = 0; i < e.craftMatrix.getSizeInventory(); i++)
        {
            if (e.craftMatrix.getStackInSlot(i).getItem() instanceof BasicTransmutationStone)
            {
                if (e.craftMatrix.getStackInSlot(i).stackTagCompound != null)
                {
                    e.craftMatrix.getStackInSlot(i).stackTagCompound.setInteger("uses", e.craftMatrix.getStackInSlot(i).stackTagCompound.getInteger("uses") - 1);
                    if (e.craftMatrix.getStackInSlot(i).stackTagCompound.getInteger("uses") < 1)
                    {
                        e.craftMatrix.setInventorySlotContents(i, null);
                        return;
                    }
                }
            }
        }
    }

When I try to craft the transmutation stone, it does not crash!

When I try to craft with a transmutation stone, it crashes.

The crash log is identical:

---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 10/1/14 1:58 PM
Description: Updating screen events

java.lang.NullPointerException: Updating screen events
at com.ilan321.transmutation.ref.CraftingHandler.ItemCraftedEvent(CraftingHandler.java:29)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_5_CraftingHandler_ItemCraftedEvent_ItemCraftedEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:51)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:122)
at cpw.mods.fml.common.FMLCommonHandler.firePlayerCraftingEvent(FMLCommonHandler.java:569)
at net.minecraft.inventory.SlotCrafting.onPickupFromSlot(SlotCrafting.java:128)
at net.minecraft.inventory.Container.slotClick(Container.java:349)
at net.minecraft.client.multiplayer.PlayerControllerMP.windowClick(PlayerControllerMP.java:482)
at net.minecraft.client.gui.inventory.GuiContainer.handleMouseClick(GuiContainer.java:678)
at net.minecraft.client.gui.inventory.GuiContainer.mouseClicked(GuiContainer.java:420)
at net.minecraft.client.gui.GuiScreen.handleMouseInput(GuiScreen.java:346)
at net.minecraft.client.gui.GuiScreen.handleInput(GuiScreen.java:315)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1730)
at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1038)
at net.minecraft.client.Minecraft.run(Minecraft.java:961)
at net.minecraft.client.main.Main.main(Main.java:164)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:134)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at GradleStart.bounce(GradleStart.java:107)
at GradleStart.startClient(GradleStart.java:100)
at GradleStart.main(GradleStart.java:55)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

 

What am I doing wrong here?

 

Add e.crafting != null before e.crafting.getItem()

That is not the problem. The

e.crafting

block is for when the player is crafting a transmutation stone. My problem is when the player crafts with the transmutation stone, for example 'stone + 1 iron = 4 ender pearl'. That is when it crashes.

 

Edit: ah nvm, it works now. I added the null check for the second block and it works. Thanks!