Hey everyone,

so im currently having some trouble with my container. Its 1 slot to charge an item and only items that are an instance of IEnergyContainerItem can be shift clicked into it. The problem is i cant seem to figure out how to get transferStackInSlot correct, iv looked at some code from other mods and tried to make my own:

    @Override
    public ItemStack transferStackInSlot(EntityPlayer par1EntityPlayer, int par2)
    {
        ItemStack itemstack = null;
        Slot slot = (Slot)this.inventorySlots.get(par2);

        if (slot != null && slot.getHasStack())
        {
            ItemStack itemstack1 = slot.getStack();
            itemstack = itemstack1.copy();

             if (par2 != 0)
            {
                if (itemstack1.getItem() instanceof IEnergyContainerItem)
                {
                    if (!this.mergeItemStack(itemstack1, 0, 0+1, false))
                    {
                        return null;
                    }
                }
                else if (par2 >= 1 && par2 < 28)
                {
                    if (!this.mergeItemStack(itemstack1, 28, 37, false))
                    {
                        return null;
                    }
                }
                else if (par2 >= 28 && par2 < 37 && !this.mergeItemStack(itemstack1, 1, 28, false))
                {
                    return null;
                }
            }
            else if (!this.mergeItemStack(itemstack1,1, 37, false))
            {
                return null;
            }

            if (itemstack1.func_190916_E() == 0)
            {
                slot.putStack((ItemStack)null);
            }
            else
            {
                slot.onSlotChanged();
            }

            if (itemstack1.func_190916_E() == itemstack.func_190916_E())
            {
                return null;
            }

            slot.func_190901_a(par1EntityPlayer, itemstack1);
        }
        return itemstack;
    }

What iv been getting is either it doesn't actually work or with this one it crashes with this crash report:

java.lang.NullPointerException: Updating screen events
	at net.minecraft.inventory.Container.slotClick(Container.java:256)
	at net.minecraft.client.multiplayer.PlayerControllerMP.windowClick(PlayerControllerMP.java:594)
	at net.minecraft.client.gui.inventory.GuiContainer.handleMouseClick(GuiContainer.java:687)
	at net.minecraft.client.gui.inventory.GuiContainer.mouseClicked(GuiContainer.java:429)
	at net.minecraft.client.gui.GuiScreen.handleMouseInput(GuiScreen.java:611)
	at net.minecraft.client.gui.GuiScreen.handleInput(GuiScreen.java:576)
	at net.minecraft.client.Minecraft.runTick(Minecraft.java:1792)
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1119)
	at net.minecraft.client.Minecraft.run(Minecraft.java:407)
	at net.minecraft.client.main.Main.main(Main.java:118)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:97)
	at GradleStart.main(GradleStart.java:26)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Can anyone tell me what i'm doing wrong/how i can actually do this to suite my needs/how to make it better

It's a NullPointerException - something is null where it shouldn't be. The full crash report will give a class and line number, so go to that place in your code and look for the problem. If you need more help to find it, post the full console log and your whole Container class.

If this is 1.11, I can see a problem immediately - null is never a valid value for an ItemStack.  Use ItemStack.EMPTY.

 

Also, what's with the func_190916_E() and func_190901_a() calls?  There are deobfuscated names for both of those:  ItemStack#getCount() and Slot#onTake().

In 1.11 and after, an ItemStack can never be null.  Return and use ItemStack.EMPTY instead of null.

 

3 minutes ago, desht said:

Also, what's with the func_190916_E() and func_190901_a() calls?  There are deobfuscated names for both of those:  ItemStack#getCount() and Slot#onTake().

 

He has not updated his mappings, that's why. OP, you should update your mappings, it will make a stuff a lot easier to read.

14 minutes ago, larsgerrits said:

In 1.11 and after, an ItemStack can never be null.  Return and use ItemStack.EMPTY instead of null.

 

He has not updated his mappings, that's why. OP, you should update your mappings, it will make a stuff a lot easier to read.

How do you update mappings?

Just now, Jay Avery said:

How do you update mappings?

In your build.gradle:

minecraft {
    ...
    mappings = snapshot_20170103
    ...
}

Or whatever's current for 1.11.2 - see http://export.mcpbot.bspk.rs/.  There isn't a "stable" mapping for 1.11.2 yet.

Derp, yeah i forgot about the null in 1.11, so i fixed that up as well as updated my mappings, but the code doesnt seem to work how id like it to, it doesnt transfer the item/block to the slot on shift click only to the top left slot or the one next to it in the inventory, and back and forth.

code with updated mappings:

 @Override
    public ItemStack transferStackInSlot(EntityPlayer par1EntityPlayer, int par2)
    {
        ItemStack itemstack = ItemStack.EMPTY;
        Slot slot = (Slot)this.inventorySlots.get(par2);

        if (slot != null && slot.getHasStack())
        {
            ItemStack itemstack1 = slot.getStack();
            itemstack = itemstack1.copy();

             if (par2 != 0)
            {
                if (itemstack1.getItem() instanceof IEnergyContainerItem)
                {
                    if (!this.mergeItemStack(itemstack1, 0, 0+1, false))
                    {
                        return ItemStack.EMPTY;
                    }
                }
                else if (par2 >= 1 && par2 < 28)
                {
                    if (!this.mergeItemStack(itemstack1, 28, 37, false))
                    {
                        return ItemStack.EMPTY;
                    }
                }
                else if (par2 >= 28 && par2 < 37 && !this.mergeItemStack(itemstack1, 1, 28, false))
                {
                    return ItemStack.EMPTY;
                }
            }
            else if (!this.mergeItemStack(itemstack1,1, 37, false))
            {
                return ItemStack.EMPTY;
            }

            if (itemstack1.getCount() == 0)
            {
                slot.putStack((ItemStack)ItemStack.EMPTY);
            }
            else
            {
                slot.onSlotChanged();
            }

            if (itemstack1.getCount() == itemstack.getCount())
            {
                return ItemStack.EMPTY;
            }

            slot.onTake(par1EntityPlayer, itemstack1);
        }
        return itemstack;
    }

 

Edited February 7, 20178 yr by abused_master

First line of your method:

ItemStack itemstack = null;

 

10 minutes ago, larsgerrits said:

First line of your method:

ItemStack itemstack = null;

 

Aha, missed that, fixed

Post your whole Container class.

 

From what you describe, you're probably using the wrong index numbers in the mergeItemStack calls. Try adding a println to the transferStackInSlot method and print the slot index (par2). Then when you test it, you can check whether the index for a particular slot is what you expect it to be.