C++中创建一个Level并添加的Runtime当中

Level.Add(GetWorld()->SpawnActor<ABuildingModLevel>());  

C++中Spawn一个基于蓝图的Actor

UWorld* const World = GetWorld(); // get a reference to the world  
if (World)   
{  
   // if world exists  
   YourClass* YC = World->SpawnActor<YourClass>(BlueprintVar, SpawnLocation, SpawnRotation);  
}

SpawnActor一般用在非构造函数中，比如BeginPlay()。

如果想在构造函数中创建Actor，一般用ConstructorHelpers::FObjectFinder。例如：

.h

TSubclassOf<YourClass> BlueprintVar;

.cpp

ClassThatWillSpawnTheBlueprint::ClassThatWillSpawnTheBlueprint(const class FPostConstructInitializeProperties& PCIP)  
    : Super(PCIP)  
{  
    static ConstructorHelpers::FObjectFinder<UBlueprint> PutNameHere(TEXT("Blueprint'/Path/To/Your/Blueprint/BP.BP'"));  
    if (PutNameHere.Object)   
    {  
        BlueprintVar = (UClass*)PutNameHere.Object->GeneratedClass;  
    }  
}

UE4其他类型的蓝图，比如Widget蓝图，都可以通过下面这种方式加载。