Notifications: tree, parent and deletion

Prefer a dedicated callback when available

For entry, readiness, frames and drawing, _EnterTree, _Ready, _Process and _Draw are usually clearer. _Notification(int what) is useful for a notification without a convenient dedicated callback or a custom notification protocol. Use SDK constant names instead of remembered numbers.

Observe real events

Run LifecycleDemo from the lifecycle guide. Both complete files are included here for copying. Journal contains parented/unparented alongside enter/ready/exit; native release adds predelete.

using System.Collections.Generic;
using Reckfell;

public partial class LifecycleProbe : Entity
{
    public List<string> Journal { get; set; } = new();
    public int Entries { get; private set; }
    public int ReadyCalls { get; private set; }
    public int Exits { get; private set; }

    private void Record(string stage) => Journal.Add(Name + ":" + stage);
    public override void _EnterTree() { Entries++; Record("enter"); }
    public override void _Ready() { ReadyCalls++; Record("ready"); }
    public override void _ExitTree() { Exits++; Record("exit"); }

    public override void _Notification(int what)
    {
        if (what == NotificationParented) Record("parented");
        if (what == NotificationUnparented) Record("unparented");
        if (what == NotificationPredelete) Record("predelete");
    }
}

using System.Collections.Generic;
using Reckfell;

public partial class LifecycleDemo : Entity
{
    public List<string> Journal { get; } = new();
    public LifecycleProbe ParentProbe { get; private set; } = null!;
    public LifecycleProbe ChildProbe { get; private set; } = null!;

    public override void _Ready()
    {
        ParentProbe = new LifecycleProbe { Name = "Parent", Journal = Journal };
        ChildProbe = new LifecycleProbe { Name = "Child", Journal = Journal };
        ParentProbe.AddChild(ChildProbe);
        AddChild(ParentProbe);
        RemoveChild(ParentProbe);
        AddChild(ParentProbe);
        RemoveChild(ParentProbe);
        ChildProbe.RequestReady();
        AddChild(ParentProbe);
        ReckfellApi.Print(string.Join(" → ", Journal));
        ReckfellApi.Print("Ready calls: Parent=" + ParentProbe.ReadyCalls + ", Child=" + ChildProbe.ReadyCalls);
    }
}

AddChild to a detached parent already sends Parented to its child, but does not join EntityTree or call _EnterTree. RemoveChild from that hierarchy sends Unparented without _ExitTree because no active-tree entry occurred. The fixture tests these cases rather than inferring behavior from notification names.

Predelete is not a C# finalizer and makes no guarantee about garbage-collector timing. The checked bridge skips Predelete for C# RefCounted scripts: do not use that callback as a guaranteed Resource cleanup hook. The example above concerns Entity. Manage ordinary Entity native lifetime through the tree, QueueFree/Free and explicit ownership of detached objects. Disconnect gameplay handlers in _ExitTree: an object can leave a level and stay alive in a cache.

A custom notification

In the group example, GroupTarget2D declares RefreshNotification = 10001. NotifyGroup delivers that value to _Notification. It is this example custom protocol value; check for collisions in your own project.

Notification is not a signal carrying arbitrary arguments: the handler receives what. Do not send system NotificationEnterTree/Ready values to imitate attachment. Actual AddChild/RemoveChild also update the tree, world, input and groups; one notification number does not replace that work.