How Do I Spawn a new object in Godot 4.x

Question

I'm currently making a game, and I want my character to shoot projectiles at the enemy. I'm facing an issue where when I click, the bullet doesn't fire. Here's my code so far:

public partial class PotatoCannon : Sprite2D
{
    public Timer cooldown;
    [Export]
    public PackedScene boolet { get; set; }
    public override void _Ready(){
            cooldown = GetNode<Timer>("CannonCooldown");
            cooldown.Autostart = false;
        }
    public override void _PhysicsProcess(double delta){
        GD.Print(cooldown.TimeLeft);
        LookAt(GetGlobalMousePosition());
        RotationDegrees = Math.Abs(RotationDegrees);
        if(RotationDegrees%360>=90.0 && RotationDegrees%360<=270.0){
            FlipV = true;
        }
        else{
            FlipV = false;
        }
        if(Input.IsActionJustPressed("shoot") && cooldown.TimeLeft == 0){
            bullet Bullet = boolet.Instantiate<bullet>();
            this.AddChild(Bullet);
            cooldown.WaitTime = 1;
            cooldown.Start();
        }
    }
}

oh and btw, the error message is

E 0:00:49:0157   PotatoCannon.cs:24 @ void PotatoCannon._PhysicsProcess(Double ): System.NullReferenceException: Object reference not set to an instance of an object.

What exactly is happening? a. nothing. b. it causes an error (which?) c. it instantiates the bullet but it does not move. d. something else? — Theraot, Jul 30 '23 at 00:16
when I left click, which is associated with "shoot", it does nothing and gives and error of `E 0:00:49:0157 PotatoCannon.cs:24 @ void PotatoCannon._PhysicsProcess(Double ): System.NullReferenceException: Object reference not set to an instance of an object.` — Nanmuhong Ye, Jul 30 '23 at 01:10
I'm guessing the line 24 that the error mentions is this `bullet Bullet = boolet.Instantiate();` correct? That would mean that the `PackedScene boolet` is not set. Double check you set it. You could try `GD.Print(boolet);` to see if it has a value. — Theraot, Jul 30 '23 at 01:20
it returns null. Is there any other way to spawn a new object using code other than this? — Nanmuhong Ye, Jul 30 '23 at 01:36
Arguably. You could build an scene `Node` by `Node` in code. However, the issue is not instantiating your scene, the issue is getting a reference to it. — Theraot, Jul 30 '23 at 01:45

score 1 · Accepted Answer · answered Jul 30 '23 at 01:49

Exported variables are supposed to be available and settable from the editor Inspector.

However, since that is not working, let us instead load PackedScene you need:

    public PackedScene boolet { get; set; }
    public override void _Ready(){
        // ...
        boolet = GD.Load<PackedScene>(PATH);
    }

Here you need to replace PATH with the "res://..." path of the bullet scene you want to instantiate.

By loading it in _Ready and storing it in the field boolet, it should be available when you need to instantiate in _PhysicsProcess.

How Do I Spawn a new object in Godot 4.x

1 Answers1