Why is OnConstruction being called *after* my function calls on the object?

Development Programming & Scripting C++
1

I have a base CPP class that attempts to dynamically set material instances in OnConstruction:


void ACPP_MyActorBase::OnConstruction(const FTransform& Transform)
  {
    // Setup Dynamic Material Instances
    for (UActorComponent *Component : GetComponentsByClass(UMeshComponent::StaticClass())) {
      UMeshComponent* MeshComponent = Cast<UMeshComponent>(Component);
      UMaterialInterface *Material = MeshComponent->GetMaterial(0);
      UMaterialInstanceDynamic *DynamicMaterialInstance = MeshComponent->CreateDynamicMaterialInstance(0, Material);
      DynamicMaterials.Add(DynamicMaterialInstance);
    )));
  }
}

I’ve been scratching my head as to why this array is empty when trying to access in my subclass’s blueprint. I ended up putting a getter to access the function that looks like this:


TArray<UMaterialInstanceDynamic*> ACPP_MyActorBase::GetDynamicMaterials()
{
  return DynamicMaterials;
}

I added some logging and stripped my code to the bare minimum, even trying to do this with a simple TArray of integers. It turns out the problem is fairly simple: the call to GetDynamicMaterials is happening before the parent OnConstruction call. Here’s the construction script of my blueprint which is a subclass of ACPP_MyActorBase:

Annotation 2020-08-09 183228.png
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I’m really baffled. I thought perhaps there was a race condition with threads, but when I pop open the debugger in visual studio, both OnConstruction and GetDynamicMaterials appear to be running in the same main thread with the same thread ID.

Why is this happening? How can I make sure the constructor has fully executed before I do other things to the object?

2

I’ll go ahead and put my “solution” here in case anyone else comes across this. Essentially, I’m defining a custom event:


UFUNCTION(BlueprintImplementableEvent)
void OnMyActorBaseConstructionFinished();

I’m then calling it at the end of my super class’s OnConstruction method. Then, in my blueprint, I’m overriding it.

3

I’ve also noticed the constructor being called on class objects more than once, and sometimes on game exit. From what I’m reading its an expected behavior?