【UE4 C++】Actor 與 Component —— 創建、銷毀

# Actor的生成與銷毀

## 創建Actor實例

- `UClass*`
- `TSubclassOf<T>`
- `SpawnActor()`

    ```cpp
    UPROPERTY(EditAnywhere, Category = "init")
    	UClass* bullet0; // 取類

    UPROPERTY(EditAnywhere, Category = "init")
    	TSubclassOf<Amissile> bullet; //取Amissile類及其派生類

    UPROPERTY(EditAnywhere, Category = "init")
    	Amissile* bullet2; // 取類的實例
    ```

    ```cpp
    GetWorld()->SpawnActor<Amissile>(bullet0, GetActorTransform());

    GetWorld()->SpawnActor<Amissile>(bullet, body->GetSocketTransform("FirePos"));

    Amissile* MissileIns = GetWorld()->SpawnActor<Amissile>(bullet2->StaticClass(), GetActorTransform());
    ```

## 銷毀

### 直接銷毀

- 使用Destroy()

    ```cpp
    MissileIns->Destroy();
    ```

### 設置生命周期

- 構造函數設置 `InitialLifeSpan`

    ```cpp
    InitialLifeSpan = 8.0f;
    ```

- BeginPlay 里使用 `SetLifeSpan()` 設置生命周期

    ```cpp
    InitialLifeSpan = 8.0f;
    ```

Component 的創建與銷毀

創建Component

構造函數創建

• CreateDefaultSubobject<T>

  UPROPERTY(VisibleAnywhere)
  	UStaticMeshComponent* paddle1;
  
  paddle1 = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("paddle1"));
  

Runtime 創建

• NewObject<T>

• RegisterComponent()

  Mesh = NewObject<UStaticMeshComponent>(this,TEXT("MyMesh"));
  Mesh->SetupAttachment(root);
  Mesh->RegisterComponent(); // 注冊渲染/物理狀態
  // 可配合 LoadObject() 
  

加載資源

FObjectFinder 構造函數加載資源

• ConstructorHelpers::FObjectFinder<T>

  static ConstructorHelpers::FObjectFinder<UStaticMesh> paddleMesh(TEXT("StaticMesh'/Game/Demo_Drone/SM/paddle.paddle'"));
  if (paddleMesh.Succeeded())
  {
  	paddle1->SetStaticMesh(paddleMesh.Object);
  }
  

LoadObject 加載資源

• LoadObject<T>

  UStaticMesh* bodyMesh = LoadObject<UStaticMesh>(this,TEXT("StaticMesh'/Game/Demo_Drone/SM/drone.drone'"));
  if (bodyMesh)
  {
  	body->SetStaticMesh(bodyMesh);
  }
  

設置組件層級關系

• 設置根組件 RootComponent 或者 SetRootComponent()

• SetupAttachment

• AttachToComponent

  RootComponent = outCollison;
  SetRootComponent(outCollison);
  
  paddle1->SetupAttachment(body, TEXT("paddle1"));
  paddle2->SetupAttachment(body, TEXT("paddle2"));
  paddle3->AttachToComponent(body, FAttachmentTransformRules::KeepRelativeTransform, TEXT("paddle3"));
  paddle4->AttachToComponent(body, FAttachmentTransformRules::KeepRelativeTransform, TEXT("paddle4"));
  
  childSceneComponent->AttachToComponent(root, FAttachmentTransformRules::SnapToTargetIncludingScale);
  

---

銷毀組件

• DestroyComponent()

• UnregisterComponent() 使用 RegisterComponent 創建，需要先注銷再銷毀

  Mesh->UnregisterComponent();
  Mesh->DestroyComponent();
  

各類組件創建與初始化

UStaticMeshComponent

paddle1 = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("paddle1"));
auto paddleMesh = ConstructorHelpers::FObjectFinder<UStaticMesh>(TEXT("StaticMesh'/Game/Demo_Drone/SM/paddle.paddle'"));
if (paddleMesh.Object != nullptr)
{
	paddle1->SetStaticMesh(paddleMesh.Object);
}

UBoxComponent

outCollison = CreateDefaultSubobject<UBoxComponent>(TEXT("outCollison"));
outCollison->SetBoxExtent(FVector(60, 60, 15));
outCollison->SetSimulatePhysics(true);
outCollison->SetCollisionProfileName(TEXT("WorldDynamic"));
outCollison->SetCollisionEnabled(ECollisionEnabled::NoCollision);

USphereComponent

sphereComp = CreateDefaultSubobject<USphereComponent>(TEXT("SphereComp"));
sphereComp->InitSphereRadius(5.0f);
sphereComp->SetCollisionProfileName(TEXT("WorldDynamic"));
sphereComp->SetGenerateOverlapEvents(true);
sphereComp->OnComponentBeginOverlap.AddDynamic(this, &Amissile::Overlaphandler);

// overlap 函數綁定
void Amissile::Overlaphandler(UPrimitiveComponent* OverlappedComponent,
				AActor* OtherActor, 
				UPrimitiveComponent* OtherComp,
				int32 OtherBodyIndex,
				bool bFromSweep,
				const FHitResult& SweepResult){}

USkeletalMeshComponent

SkeletalMeshComp = CreateDefaultSubobject<USkeletalMeshComponent>(TEXT("SkeletalMeshComp"));
SkeletalMeshComp->SetGenerateOverlapEvents(true);
SkeletalMeshComp->SetSimulatePhysics(true);

USpringArmComponent 和 UCameraComponent

springArmComp = CreateDefaultSubobject<USpringArmComponent>(TEXT("SpringArm"));
springArmComp->SetupAttachment(RootComponent);
cameraComp = CreateDefaultSubobject<UCameraComponent>(TEXT("Camera"));
cameraComp->SetupAttachment(springArmComp);

UPhysicsThrusterComponent

upThrusterComp = CreateDefaultSubobject<UPhysicsThrusterComponent>(TEXT("upThrusterComp"));
upThrusterComp->SetupAttachment(RootComponent);
upThrusterComp->SetWorldRotation(UKismetMathLibrary::MakeRotFromX(FVector(-this->GetActorUpVector())));
upThrusterComp->ThrustStrength = 980.0f;
upThrusterComp->SetAutoActivate(true);

UTextRenderComponent

CountdownText = CreateDefaultSubobject<UTextRenderComponent>(TEXT("CountdownNumber"));
CountdownText->SetHorizontalAlignment(EHTA_Center);
CountdownText->SetWorldSize(150.0f);
CountdownText->AttachTo(RootComponent);
CountdownTime = 3;
CountdownText->SetText(FString::FromInt(FMath::Max(CountdownTime, 0)));

projectileMovementComp = CreateDefaultSubobject<UProjectileMovementComponent>(TEXT("projectileMovement"));
projectileMovementComp->InitialSpeed = 500.0f;

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