Daniel's Notes

Node Lifecycle in Godot

3 min read

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:

  1. the constructor (MyObject.new())
  2. _init()
  3. _enter_tree()
    • (This happens after the node is added to the Scene Tree using add_Child())
  4. ready in Godot
    • This happens after every child node1 has been initialized, added to the scene, tree and has already called _ready().

_init() usually is called after the constructor finishes

It 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 it2:

  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.3
  2. _init() assignment: the property’s value is replaced by any assignments made in _init(), triggering the setter.
  3. 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

Quote

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() in Godot|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

Footnotes

  1. recursively ↩

  2. See docs here ↩

  3. This appears to only be true when using GDScript. When the setter is defined another language such as Swift or C# then the setter appears to follow whatever the language determines. ↩

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