RootComponent in actor constructor

Development Programming & Scripting C++
1

Why RootComponent is used in https://docs.unrealengine.com/en-US/…art/index.html as SetupAttachment argument?
In constructor it seems it’s always null even after the first SetupAttachement.

Using it multiple times in constructor for attaching several components trigger strange behaviours.

2

RootComponent is the parent of all components of an Actor:

You can see a better explanation about RootComponent in this video:
C++ Tanks vs Zombies | 01 | Live Training | Unreal Engine

If you don’t set a value for it Unreal will do it for you. You can see it in Actor.cpp:


/** Util that sets up the actor's component hierarchy (when users forget to do so, in their native ctor) */
static USceneComponent* FixupNativeActorComponents(AActor* Actor)
{
    ...
}

That is called in:


void AActor::PostSpawnInitialize(...)
{
    // General flow here is like so
    // - Actor sets up the basics.
    // - Actor gets PreInitializeComponents()
    // - Actor constructs itself, after which its components should be fully assembled
    // - Actor components get OnComponentCreated
    // - Actor components get InitializeComponent
    // - Actor gets PostInitializeComponents() once everything is set up
    //
    // This should be the same sequence for deferred or nondeferred spawning.

I usually do as explained in the video without problems.

3

Thank you, I hoped this kind of explanation could be found in the documentation :slight_smile: Perhaps I should think about the source code as a good source of information.