Setting the root component in a code class constructor does not actually set that component as the root component of a Blueprint created from that class.

The root component of a Blueprint is determined by the order in which the components are defined in the constructor of a class (the component defined first becomes the root component). Trying to set a different component as the root component does not work.

1. Create a new code project using the First Person template.
2. Build the project in Visual Studio.
3. Open the project in the Editor.
4. Add a new code class to the project derived from Actor. Name the class MyActor.
5. Close the Editor.
6. In the header file for the new class, add the following code:

   public:
   	UPROPERTY(VisibleAnywhere, BlueprintReadOnly)
   	UStaticMeshComponent* TheMesh;
   
   	UPROPERTY(VisibleAnywhere, BlueprintReadOnly)
   	USphereComponent* TheSphere;
   
   	AMyActor(const FObjectInitializer& ObjectInitializer);
   

7. In the code file for the new class, add the following code:

   AMyActor::AMyActor(const FObjectInitializer& ObjectInitializer)
   	: Super(ObjectInitializer)
   {
   	TheSphere = ObjectInitializer.CreateDefaultSubobject<USphereComponent>(this, TEXT("TheSphere"));
   
   	TheMesh = ObjectInitializer.CreateDefaultSubobject<UStaticMeshComponent>(this, TEXT("TheMesh"));
   
   	RootComponent = TheMesh;
   }
   

8. Build the project in Visual Studio.
9. Open the project in the Editor.
10. Create a new Blueprint derived from the new MyActor class.
11. Open the Blueprint and go to the Components tab.

RESULTS:
TheSphere component is still the root component.

EXPECTED:
TheMesh component is the root component.

Setting RootComponent in C++ constructor doesn't actually change the root component