Save and load problem

Question

Hi........................ ## (Godot v3.1.1) ##
i use this script for saving and loading game..

extends Node

const SAVE_PATH = "res://save.json"

func _ready():

    load_game()


func save_game():

    var save_file = File.new()
    save_file.open(SAVE_PATH, File.WRITE)
    var save_dict = {}
    var nodes_to_save = get_tree().get_nodes_in_group("Settings")
    for node in nodes_to_save:
        save_dict[node.get_path()] = node.save()
    save_file.store_line(to_json(save_dict))
    save_file.close()

func load_game():
    var save_file = File.new()
    if not save_file.file_exists(SAVE_PATH):
        print("The save file does not exist.")
        return
    save_file.open(SAVE_PATH, File.READ)
    var data = parse_json(save_file.get_as_text())
    for node_path in data.keys():
        var node_data = data[node_path]
        get_node(node_path).load_state(node_data)

now, i have two scene: scene1 & scene2... both of them are in "Settings" group..
loading and saving in scene1 works fine.. i add these line to achive this..

func _ready():                            #i want to save a boolean value
    SavedGame.load_game()
.
.
.
func _on_Timer5_timeout():         #this function triggers with a timer
    SavedGame.save_game()
.
.
func save():
    var save_dict = {
        first_time = false
    }
    return save_dict

func load_state(data):
    for attribute in data:
        if attribute == 'first_time':
            first_run = false
        else:
            set(attribute, data[attribute])

but loading and saving in scene2 does not work and godot shows this error:
"Attempt to call function 'load_state' in base 'null instance' on a null instance."

var player_name          #i want to save player's name in scene2
func _ready():
    SavedGame.load_game()
.
.
func _on_OK_button_up():
    SavedGame.save_game()
.
.
func save():
    var save_dict = {
        player_name = player_name
    }
    return save_dict

func load_state(data):
    for attribute in data:
        if attribute == 'player_name':
            player_name = attribute
        else:
            set(attribute, data[attribute])

what am i doing wrong in scene2? thank you for your time :)

Comments

This error message sounds like the node or node path for scene2 is somewhat wrong or empty. Another possibility is that there's no script with load_state() and save() methods attached to scene2.

Maybe put some print statements in your code to show the node name for which these methods are called (& maybe for other values you desire to know).

---

First, something general:
Don't use res:// for user save path. Use user://
This is because several platforms/operating systems will disallow writing to res://.

I have no idea, why the node paths differ. How & when do you instantiate those scenes and how the scene tree actually looks like?

Maybe do a function to dump the scene tree to see if scene2 is present multiple times in different locations. This looks like somebody has added an(other) instance of the scene2 to gettree().getroot().

Personally, I use a global singleton/script for holding/saving game settings which is accessed by scenes/nodes when required but that naturally depends on game type and your design decisions.

---

Probably you try to load the settings file without even checking if the file is there and contains data.

res:// and user:// are two different paths. So files you previously saved to res:// will not be in user://.

The change from res:// to user:// was not to correct your current error but to prevent future errors. Imagine a program trying to write to C:\Program files... in Windows where such a game might be installed. This will most likely be prohibited. Similar on mobile devices.

---

ok. finally i separated savedgames of these two scenes.. i created two autoloads for saving in scene1 & scene2 separately.. now it works fine, maybe this ridiculous way for saving just works like this and can't save data with multiple separated scenes at once...