So I want to create scrollbar that is going to be apart of my custom storage device for my mod, which is going to sort and display items based of their NBT values so that it would be more storage efficient for the player to use. I have tried basing my code off the method that vanilla does for the creative inventory, and I am currently having a issue where when I change the size of the game window the game crashes with a null pointer exception.

 

Crash Log

Container Class

public class SoulChamberContainer extends Container {

  TileEntityChamber chamber;
  GuiChamber gui;
    public static TileEntityChamber chamberInv;
    public NonNullList<ItemStack> list = NonNullList.<ItemStack>create();




    public SoulChamberContainer(InventoryPlayer playerInv, final TileEntityChamber chamber){
        this.chamber = chamber;

        IItemHandler inventory = chamber.getCapability(CapabilityItemHandler.ITEM_HANDLER_CAPABILITY, EnumFacing.NORTH);


        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 9; j++) {
                addSlotToContainer(new Slot(playerInv, j + i * 9 + 9, 8 + j * 18, 140 + i * 18));
            }
        }

        for (int j = 0; j < 12; ++j)
        {
            for (int k = 0; k < 4; ++k)
            {
                addSlotToContainer(new soulChamberSlot(inventory, k + j * 4, 80 + k * 18, 18 + j * 18) {
                    @Override
                    public void onSlotChanged() {
                        chamber.markDirty();
                    }
                });

            }
        }




        for (int k = 0; k < 9; k++) {
            addSlotToContainer(new Slot(playerInv, k, 8 + k * 18, 198));
        }

    }



    public void scrollTo(float pos)
    {
        int i = (this.list.size() + 9 - 1) / 9 - 5;
        int j = (int)((double)(pos * (float)i) + 0.5D);

        if (j < 0)
        {
            j = 0;
        }

        for (int k = 0; k < 5; ++k)
        {
            for (int l = 0; l < 9; ++l)
            {
                int i1 = l + (k + j) * 9;

                if (i1 >= 0 && i1 < this.list.size())
                {
                    gui.setInventorySlotContents(l + k * 9, (ItemStack) this.list.get(i1));
                }
                else
                {
                    gui.setInventorySlotContents(l + k * 9, ItemStack.EMPTY);
                }
            }
        }
    }







    public boolean moreThan1PageItems()
    {
        return this.list.size() > 24;
    }



    @Override
    public boolean canInteractWith(EntityPlayer playerIn) {
        return true;
    }


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

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

                int containerSlots = inventorySlots.size() - player.inventory.mainInventory.size();

                if (index < containerSlots) {
                    if (!this.mergeItemStack(itemstack1, containerSlots, inventorySlots.size(), true)) {
                        return ItemStack.EMPTY;
                    }
                } else if (!this.mergeItemStack(itemstack1, 0, containerSlots, false)) {
                    return ItemStack.EMPTY;
                }

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

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

                slot.onTake(player, itemstack1);
            }


        return itemstack;
    }
    }

 

 

GUI Class

public class GuiChamber extends GuiContainer {
    private static final ResourceLocation BACKGROUND = new ResourceLocation(soulomancy.MODID, "textures/gui/chamber.png");

    public NonNullList<ItemStack> list = NonNullList.<ItemStack>create();


    int ScrollRow = 0;
    private boolean isScrolling = false;
    private boolean wasClicking = false;
    private float scrollCurrent;
    public static TileEntityChamber chamberInv;
    private static SoulChamberContainer chamContainer;


    private InventoryPlayer playerInv;
    public GuiChamber (Container container, InventoryPlayer playerInv) {
        super(container);
        this.playerInv = playerInv;
    }




    @Override
    public void initGui() {
        super.initGui();
        this.buttonList.add(new GuiButton(1, 100, 200, 100, 20, "Button id: 1"));
        ItemStack is;
        for (int i = 0; i < 48; ++i)
        {
            if (!(chamberInv.getStackInSlot(i) == null)) {
                is = chamberInv.getStackInSlot(i);
            }else {
                is = ItemStack.EMPTY;
            }

            if (!(is == null))
            {
                this.list.add(is);
                chamContainer.list = this.list;


            }

        }

    }

    @Override
    public void updateScreen()
    {
        super.updateScreen();
    }


    @Override
    protected void actionPerformed(GuiButton button) throws IOException {
        if (button.id == 1){
            System.out.println("Button id 1: Test");
        }
    }

    @Override
    public void drawScreen(int mouseX, int mouseY, float partialTicks) {
        this.drawDefaultBackground();
        super.drawScreen(mouseX, mouseY, partialTicks);
        this.renderHoveredToolTip(mouseX, mouseY);
      //  Slot slot
        boolean flag = Mouse.isButtonDown(0);
        int k = this.guiLeft;
        int l = this.guiTop;
        int i1 = k + 175;
        int j1 = l + 18;
        int k1 = i1 + 14;
        int l1 = j1 + 108;

        if (!this.wasClicking && flag && mouseX >= i1 && mouseY >= j1 && mouseX < k1 && mouseY < l1) {
            this.isScrolling = this.needsScrollBars();
            System.out.println("DEBUG: Scrollbar Needed");
        }

        if (!flag) {
            this.isScrolling = false;
            System.out.println("DEBUG: Not Scrolling");
        } else {


        }

        this.wasClicking = flag;

        if (this.isScrolling) {
            System.out.println("DEBUG: Is Scrolling");
            this.scrollCurrent = (mouseY - j1 - 7.5F) / (l1 - j1 - 15.0F);
            this.scrollCurrent = MathHelper.clamp(this.scrollCurrent, 0.0F, 1.0F);
            chamContainer.scrollTo(this.scrollCurrent);
        }



    }

    public void handleMouseInput() throws IOException
    {
        super.handleMouseInput();
        int i = Mouse.getEventDWheel();

        if (i != 0 && this.needsScrollBars())
        {
            int j = (((SoulChamberContainer)this.inventorySlots).list.size() + 9 - 1) / 9 - 5;

            if (i > 0)
            {
                i = 1;
            }

            if (i < 0)
            {
                i = -1;
            }

            this.scrollCurrent = (float)((double)this.scrollCurrent - (double)i / (double)j);
            this.scrollCurrent = MathHelper.clamp(this.scrollCurrent, 0.0F, 1.0F);
            ((SoulChamberContainer)this.inventorySlots).scrollTo(this.scrollCurrent);
        }
    }




    private boolean needsScrollBars()
    {
        if (((SoulChamberContainer)this.inventorySlots).moreThan1PageItems())
        {
            return false;
        }
        else
        {
           return true;
        }
    }






    public void setInventorySlotContents(int i, ItemStack itemStack)
    {
        chamberInv.invContents(i, itemStack);

        if (itemStack != null && itemStack.getCount() > 64)
        {
            itemStack.setCount(64);
        }
        chamberInv.markDirty();
    }







    @Override
    protected void drawGuiContainerBackgroundLayer(float partialTicks, int mouseX, int mouseY) {
        GlStateManager.color(1, 1, 1, 1);
        mc.getTextureManager().bindTexture(BACKGROUND);
        int x = (width - xSize) / 2;
        int y = (height - ySize) / 2;
        drawTexturedModalRect(x, y, 0, 0, xSize, 222);

        GL11.glColor4f(1.0F, 1.0F, 1.0F, 1.0F);
        int var5 = (this.width - this.xSize) / 2;
        int var6 = (this.height - this.ySize) / 2;
        this.drawTexturedModalRect(var5, var6, 0, 0, this.xSize, this.ySize);
        int i1 = this.guiLeft + 153;
        int k = this.guiTop + 18;
        int l = k + 90;
        if (needsScrollBars())
        {
            System.out.println("Scroll Activated");
            this.drawString(mc.fontRenderer, "fart", 172, 220, 0xffffff);
            this.drawTexturedModalRect(i1, k + (int)((float)(l - k - 17) * this.scrollCurrent), 0,198, 12, 15);
        }
        else
        {
            this.drawTexturedModalRect(i1, k, 12, 198, 12, 15);

        }

    }

    @Override
    protected void drawGuiContainerForegroundLayer(int mouseX, int mouseY) {
        String name = I18n.format(ModBlocks.soulChamber.getUnlocalizedName() + ".name");
        fontRenderer.drawString(name, xSize / 2 - fontRenderer.getStringWidth(name) / 2, 6, 0x404040);
        fontRenderer.drawString(playerInv.getDisplayName().getUnformattedText(), 8, 222 - 94, 0x404040);
    }

    public int rowsVisible() {
        return 6;
    }

}

 

Tile Entity Class 

public class TileEntityChamber extends TileEntity {

private ItemStackHandler inv = new ItemStackHandler(48);
    private final NonNullList<ItemStack> inventoryContents = NonNullList.withSize(48, net.minecraft.item.ItemStack.EMPTY);


        public void invContents(int i, ItemStack stack){
                this.inventoryContents.set(i, stack);

        }



        public ItemStack getStackInSlot(int i){

                  return i >= 48 ? ItemStack.EMPTY : this.inventoryContents.get(i);
        }

    @Override
    public void markDirty() {
        super.markDirty();
    }




    public ItemStackHandler getInv() {
        return inv;
    }

    @Override
    public NBTTagCompound writeToNBT(NBTTagCompound compound) {
        compound.setTag("inventory", inv.serializeNBT());
        return super.writeToNBT(compound);
    }

    @Override
    public void readFromNBT(NBTTagCompound compound) {
        inv.deserializeNBT(compound.getCompoundTag("inventory"));
        super.readFromNBT(compound);
    }

    @Override
    public boolean hasCapability(Capability<?> capability, @Nullable EnumFacing facing) {
        return capability == CapabilityItemHandler.ITEM_HANDLER_CAPABILITY || super.hasCapability(capability, facing);
    }

    @Nullable
    @Override
    public <T> T getCapability(Capability<T> capability, @Nullable EnumFacing facing) {
        return capability == CapabilityItemHandler.ITEM_HANDLER_CAPABILITY ? (T)inv: super.getCapability(capability, facing);
    }
}

 

 

Also I would like insight on how you would go about having only a certain amount of slots show up per "page", so like I only want 24 slots showing up but as you scroll of course new slots show up.

Caused by: java.lang.NullPointerException

    at com.quinn50.soulomancy.blocks.soulChamber.SoulChamberContainer.scrollTo(SoulChamberContainer.java:91) ~[SoulChamberContainer.class:?]

    at com.quinn50.soulomancy.blocks.soulChamber.GuiChamber.handleMouseInput(GuiChamber.java:154) ~[GuiChamber.class:?]

    at net.minecraft.client.gui.GuiScreen.handleInput(GuiScreen.java:576) ~[GuiScreen.class:?]

It might have something to do with scaled resolution? Try placing conditional breakpoints and find out what is null

Edited September 1, 20187 yr by Cadiboo

Inventory was not being set to the container so whenever initgui was called it was null causing the crash