I have a problem with child scripts.

[undone python]

Translation to English:

I have a problem with child scripts.
For example, there is a parent script that contains a variable, and this variable is initialized — meaning it holds a reference to a node. However, when I call this variable in the child script to get this reference, it throws a Null error. Although the variable is definitely initialized in time, because right before calling the function in the child script from the parent script, I print this variable to the console, and it’s not null.

Please help, because I’ve been struggling with this for a long time. Or maybe someone can explain how to properly use child scripts, etc. I can show my script where the error occurs if needed.

[sterile ether]

Please show the code in question, you might be missing/misunderstanding something there.

[undone python]

Translation to English:

It might be difficult for you to understand what I’ve shown, so feel free to ask questions. Unfortunately, I don’t speak English well enough to explain it in a video.

In the video, I realized that maybe the problem is not exactly with the variable itself.

[dusty scarab]

I’m seeing WEAPON is defined in GameCharacterControl, not Inventory, correct? That’s the problem… if you want WEAPON in the child script, you’ll need a reference to that instance of GameCharacterControl

[undone python]

Why define it in Inventory if Inventory is a child script of GameCharacterControl? The whole point of the GameCharacterControl script is that it contains the variables with the references I need. Instead of creating this variable every time, I just take it from the parent script.

maybe I don't understand something

[sterile ether]

(please use "reply" option if you want me to get notified 🙃)
I'd guess some GameCharacterControl._ready is called before Inventary._ready is resumed and hence the %Inventary.load_invtentary("slot") fails as its WEAPON is not yet initilized.

Comment out that %Invantory.load_invtentary("slot") call, replace the preceding print(WEAPON) with:

print("%s" % [self.get_path()])
print(" %-20s = %s" % ["self", self])
print(" %-20s = %s" % ["self.WEAPON", self.WEAPON])
print(" %-20s = %s" % ["%Inventary", %Inventary])
print(" %-20s = %s" % ["%Inventary.WEAPON", %Inventary.WEAPON])

and try making sense of the output.

[dusty scarab]

A child script doesn’t inherit a parent’s variables/state, perhaps that’s the misunderstanding? There needs to be an explicit reference to the class/script that owns the variable (or an alternative way to do it)

Perhaps here, to get it working, try get_parent().WEAPON

[sterile ether]

His Invantory is a child of GameCharacterControl, and the script used by Invantory extends GameCharacterControl script.

[dusty scarab]

Yeah tough to see that in the video, sorry - I think your ordering might be right but I’d also wonder which weapon variable is being wanted here if both parent and child scripts have their own instance

[undone python]

/root/TestMechanic/1/Game_Character_Control/InputPlayer
self = InputPlayer:<Node#59944994668>
self.WEAPON = Weapon:<Node3D#59374569290>
%Inventary = Inventary:<Node#60012103536>
%Inventary.WEAPON = <null>

Translation to English:

Input_Player is also a child script of GameCharacterControl. I created it to move all key inputs there because the CharacterBody3D script was too overloaded (so to speak, script optimization).
Here’s what relates to Inventory, there is:
func _input(event):
if Input.is_action_just_pressed("Weapon1"):
%Inventary._load_inventary("slot1")
if Input.is_action_just_pressed("Weapon2"):
%Inventary._load_inventary("slot2")
if Input.is_action_just_pressed("Weapon3"):
%Inventary._load_inventary("slot3")

I just noticed that I spelled the word inventory incorrectly, sorry🤦

[undone python]

Maybe I don't understand how to use child scripts at all. I just copied it from the tutorial where it seems to work successfully.

[sterile ether]

Yeah it's just about the order of operations. _ready is called for these nodes in the order as shown below, and in the same order the await owner.readys are resumed (assuming all these nodes run GameCharacterControl._ready).

Meaning when GameCharacterControl._ready is resumed for node 1 (InputPlayer), at that moment for nodes marked as 2/3/4/5/6 their relevant members (like WEAPON) are not yet initialized. And that's why %Inventary._load_inventary("slot1") called from node 1's _ready was throwing null reference error.

Besides, with your code note that even if %Inventary._load_inventary("slot1") would not fail/crash, it would be called six times, once for each of these nodes (which I doubt is what you want).

[dusty scarab]

Which tutorial? Worth double-checking the code against the source material. Here, I think because Inventory has its own variable, it would also need initialising (I don’t see that in the video as you only show the inspector for the parent script). Inventory is its own script; it isn’t related to its parent at all and needs its own WEAPON assignment (check this in the inspector).

[dusty scarab]

Obviously the intention isn’t to have two instances so something needs tidying up; if the inventory needs a weapon then declare it there and assign it in the inspector rather than extend the other class (or grab the reference/pass it in to the inventory, and so on)