How to add multiple instances of a 3D scene in Godot 3?

Question

I'm using Godot 3.0.6. I am able to instantiate a scene by pressing a key, but only once. Here is my code in GDScript:

extends KinematicBody

var cube = load("res://Scenes/Cube.tscn").instance()
var ball
var velocity

func _ready():
    ball = get_node(".")

func _process(delta):
    pass

func _physics_process(delta):
    if Input.is_action_pressed("ui_up"):
        get_tree().get_root().add_child(cube)

If I try adding more than one cube into the scene, I get an error:

Can't add child 'Cube' to 'root', already has a parent 'root'.

What am I doing wrong?

Answer 1

You're trying to add the same cube instance to the scene tree repeatedly. Just load the scene and don't create an instance immediately. Create the new instances when the key gets pressed and add them to the scene tree.

var cube = preload("res://Scenes/Cube.tscn")

func _physics_process(delta):
    if Input.is_action_pressed("ui_up"):
        # Create a new instance here.
        get_tree().get_root().add_child(cube.instance())