Node Lifecycle in Godot
Order
Inserting a node into the scene tree
As far as I can tell from the docs this is the order of events when creating a new node and adding it:
- the constructor (
MyObject.new()) _init()_enter_tree()- (This happens after the node is added to the Scene Tree using
add_Child())
- (This happens after the node is added to the Scene Tree using
- ready in Godot
- This happens after every child node3 has been initialized, added to the scene, tree and has already called
_ready().
- This happens after every child node3 has been initialized, added to the scene, tree and has already called
_init() usually is called after the constructor finishesIt seems that we should assume that _init() will be called after the constructor, but unfortunately Godot doesn't seem to guarantee the order? Read this from the docs
"_init() is Called when the object's script is instantiated, oftentimes after the object is initialized in memory (through Object.new() in GDScript, or new GodotObject in C#). It can be also defined to take in parameters. This method is similar to a constructor in most programming languages."
Instantiating a scene
As for as I can tell from the docs, this is the order of events when instantiating a scene and adding it[1]:
- Initial value assignment: the property is assigned its initialization value, or its default value if one is not specified. If a setter exists, it is not used.[2]
_init()assignment: the property's value is replaced by any assignments made in_init(), triggering the setter.- Exported value assignment: an exported property's value is again replaced by any value set in the Inspector, triggering the setter.
GDScript Example
# test is initialized to "one", without triggering the setter.
@export var test: String = "one":
set(value):
test = value + "!"
func _init():
# Triggers the setter, changing test's value from "one" to "two!".
test = "two"
# If someone sets test to "three" from the Inspector, it would trigger
# the setter, changing test's value from "two!" to "three!".
Gotcha: Setting a Resource type in the inspector and leaving all its properties at default values
From: Godot notifications — Godot Engine (stable) documentation in English @ User-contributed notes:
There's a gotcha with object initialization. When setting Resource types in the inspector, and leaving all its @exported Variant data members (for example) at default values, the default values will overwrite values set in its _init() function as if they were set via the inspector. Example below:
(https://docs.godotengine.org/en/stable/tutorials/best_practices/godot_notifications.html#init-vs-initialization-vs-export)
class_name MyResource extends Resource
@export var my_int: int = -1
func _init() -> void:
if my_int < 0: my_int = 2
class_name MyNode extends Node
@export var my_resource := MyResource.new()
If my_resource is set in the inspector, MyResource.my_int will be -1. If my_resource isn't set via inspector, it will be 2.
Work-around: Implement a private initialization() function that you call_deferred() at the end of the _init() function. The deferred function will execute after the @export properties are initialized so are overwritten.
Docs
See Also
- Godot 4 and GDScript - Part 3 (the lifecycle)
3: recursively