gistfile1.java

//GUI Handler Class
public class GuiHandler implements IGuiHandler {

	public GuiHandler() {
		NetworkRegistry.instance().registerGuiHandler(MultiLink.instance, this);
	}
	
	@Override
	public Object getServerGuiElement(int ID, EntityPlayer player, World world, int x, int y, int z) {
		System.out.println("Server Gui");
		switch(ID) {
			case 0:
				ItemStack stack = player.getHeldItem();
				Item item = stack.getItem();
				if (item instanceof ItemLinkHolder) {
					InventoryLinkHolder inv = new InventoryLinkHolder();
					if (inv != null) {
						System.out.println("Server returned");
						return new ContainerLinkHolder(player.inventory, stack, inv);
					}
				}
				break;
		}
		return null;
	}

	@Override
	public Object getClientGuiElement(int ID, EntityPlayer player, World world, int x, int y, int z) {
		System.out.println("Client Gui");
		switch(ID) {
		case 0:
			ItemStack stack = player.getHeldItem();
			Item item = stack.getItem();
			if (item instanceof ItemLinkHolder) {
				InventoryLinkHolder inv = new InventoryLinkHolder();
				if (inv != null) {
					System.out.println("Client returned");
					return new GuiLinkHolder(player.inventory, stack, inv);
				}
			}
			break;
		}
		return null;
	}

}

//When openGUI is called
@Override
	public ItemStack onItemRightClick(ItemStack itemstack, World world, EntityPlayer player) {
		if (player.isSneaking()) {
			if (!world.isRemote) {
				player.openGui(MultiLink.instance, 0, player.worldObj, (int) player.posX, (int) player.posY, (int) player.posZ);
			}
			return itemstack;
		}
}