GD3/4 Could not preload resource "res://inventory/Slot.gd"

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GD3/4 Could not preload resource "res://inventory/Slot.gd"

Gowydot

Hi, I have been following Inventory tutorial by Arkeve. I am at the part to add mouse wheel scrolling on the hotbar.

When I added the line "and PlayerInventory.active_item_slot == slot_index" to Slot.gd the error "Could not preload" appears on the PlayerInventory.gd.

#Slot.gd

extends Panel

var slot_index

func _ready():
	...
	refresh_style()

func refresh_style():

	# The *and PlayerInventory..* line causes error

	if SlotType.HOTBAR == slot_type and PlayerInventory.active_item_slot == slot_index:
		set('theme_override_styles/panel', selected_style)
	elif item == null:
		set('theme_override_styles/panel', empty_style)
	else:
		set('theme_override_styles/panel', default_style)

func pickFromSlot():
	...
	refresh_style()
func putIntoSlot(new_item):
	...
	refresh_style()
func initialized_item(item_name, item_quantity):
	...
	refresh_style()

#PlayerInventory.gd

extends Node

#Could not preload resource "res://inventory/Slot.gd"
const SlotClass = preload("res://inventory/Slot.gd") 
var active_item_slot = 0

func active_item_scroll_up():
	active_item_slot = (active_item_slot + 1) % NUM_HOTBAR_SLOTS
	emit_signal("active_item_updated")
func active_item_scroll_down():
	if active_item_slot == 0:
		active_item_slot = NUM_HOTBAR_SLOTS -1
	else:
		active_item_slot -= 1
	emit_signal("active_item_updated")

~~These 2 scripts are not attached to scene.~~
Slot.gd is attached to slot panel
PlayerInventory.gd is autoload.
Preload was working fine until that line is added
There is a minor difference in tutorial's and my tree set up (not sure if relevant).

Does any know why it causes this error and how to fix it? Thank you.

Megalomaniak

you might want to double check what can and can't be a constant.

https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_basics.html#constants

Gowydot

But the project in the video (GD3) works and my project (GD4) works fine up until I add that particular line. The only difference I can think of is how the tree is set up:

Tutorial:
World
-UserInterface
--Inventory
--Hotbar

Mine:
World
-Inventory
-Hotbar

Other than that I have no clue why it causes error. Godot4 updated something in script maybe?

cybereality

In general, constants must be primitive values, or values that can be deduced by the compiler. Using load (or preload) is a function, so it's return value can be variable, and also could fail, and the compiler cannot know whether the file exists, or if there is an error, etc. So I don't think that would work. Even if it worked, I'm not sure how it would offer any benefit over using var.

Megalomaniak

To be clear I don't know that this is the cause of the error, it's just the first thing that jumps out at me.

Gowydot

When I changed from const to var I got the error "SlotClass is a variable but does not contain a type"

cybereality

Preload has to use @onready

@onready var slot = preload("path/to/file")

cybereality

Also, I'd have to check the docs, but load/preload are for resources, and it may be that a script is not a resource.

Gowydot

Thanks but It still gives out the preload error.

I will just try update the tutorial project to GD4 to see if it has this problem too.

cybereality

Are you sure that file exists? I just tested and I don't see any errors.

Gowydot

You mean in my project? Yes, the Slot.gd is always there and working fine prior adding this particular code:
PlayerInventory.active_item_slot == slot_index

The Tutorial's project is working fine on 3.x but I convert its script to 4 as I follow along for my project. Maybe I will upload my project so ppl can have a check.

cybereality

So the path is correct, because it will tell you if the file doesn't exist. Most likely, there is an error in the code, for example a cyclic reference.

Gowydot

~~So I quickly convert the tutorial file to GD4 and no preload error show when run. There is probably something wrong somewhere with my code, as you said. I will try checking my codes against his.~~

Wait no, I'm so stupid. I commented that line out. When I add the line in the converted tutorial file also gives me Could not preload resource Slot.gd error.
Maybe something changed in GD4.

Gowydot

Here is my project (tested with GD4a15). The original tutorial is GD3 for 2D but I converted to GD4 for 3D.

If anyone would like to have a look because I'm not sure if it's my coding mistake or this part of tutorial is just not compatable with GD4.

https://github.com/j3du/inventorytest

Slot.gd is actually attached to panel slot.

Slot.gd part that causes error:

func refresh_style():
#	PlayerInventory.active_item_slot == slot_index
	if SlotType.HOTBAR == slot_type and PlayerInventory.active_item_slot == slot_index:
		set('theme_override_styles/panel', selected_style)

Error appears at PlayerInventory.gd.
const SlotClass = preload("res://inventory/Slot.gd")

Thanks for the help.

cybereality

Looks like a cyclic reference. The scripts cannot access each other like that (one loads one, then the other loads the first one, again forever).

Megalomaniak

cybereality cyclic reference

Yeah, those are never good.

Gowydot It works in 3.x

You've probably just gotten very, very lucky through sheer chance so far with it...

Gowydot

@cybereality It works in 3.x so this just means GD4 not allow it anymore? What can I do to fix it.

I updated my github link to include relevant folders

ALBATI_2005

Can I ask something odd... why does this const SlotClass = preload("res://inventory/Slot.gd") even exist? Just remove the line; I don't see it used anywhere in the code you've given. (NOTE: I have NOT checked the whole project). But, if there is some use to it, you can simply substitute it with some other resource, var, etc.

Gowydot

ALBATI_2005

You can check out the PlayerInventory.gd here as I do not know how to explain it myself, I just follow the tutorial.
https://github.com/j3du/inventorytest/blob/main/gd4_inventory_arkeve_proj_08_hotbar_scroll_error%20-%20Copy/inventory/PlayerInventory.gd

@Megalomaniak @cybereality
cyclic reference
So I take it that GD4 doesn't allow that to happen anymore. I will just moving on then, thanks all.

Gowydot

cybereality Yeah I wouldn't know anything about that, I just want to learn some Inventory so I can use it for 4.x. I will follow the final chapter of this tutorial and see if anything will go wrong.

I really should give a shoutout to ALBATI_2005 as he did gave the right answer for this problem 👍️ (back then I didn't understand the errors that came after deleting it)

cybereality

No it didn't work in Godot 3 either, and most programming languages. It's probably just an error/bug in your code.