UE4基礎：Gameplay框架（三）Actor 類（5月27日 更新）

本文是老王學習UE4的筆記，如有錯誤敬請指正

概述

AActor繼承於UObject是所有可以放置到場景中的對象的基類。Gameplay框架的核心基類之一。

UCLASS聲明

AActor的UCLASS已經聲明瞭BlueprintType, Blueprintable這兩個屬性都可以傳遞給子類。

UCLASS(BlueprintType, Blueprintable, config=Engine, meta=(ShortTooltip="An Actor is an object that can be placed or spawned in the world."))
class ENGINE_API AActor : public UObject
{
	GENERATED_BODY()
	...
}

生命週期

protected:
	virtual void BeginPlay() override;
	virtual void EndPlay(const EEndPlayReason::Type EndPlayReason) override;
public:	
	virtual void Tick(float DeltaTime) override;

Tick相當於Unity中的Update，UE4中的Tick可以通過PrimaryActorTick.bCanEverTick來開關。

virtual void Tick( float DeltaSeconds );
FORCEINLINE bool CanEverTick() const { return PrimaryActorTick.bCanEverTick; }
UPROPERTY(EditDefaultsOnly, Category=Tick)
	struct FActorTickFunction PrimaryActorTick;

獲取ULevel和UGameInstance

UWorld在UObject中就可以獲取

• 獲取所屬ULevel

ULevel* GetLevel() const;

• 獲取UGameInstance

class UGameInstance* GetGameInstance() const;

Actor的名字

//定義在基類UObjectBaseUtility中
public：
FORCEINLINE FString GetName() const
	{
		return GetFName().ToString();
	}

和組件相關的一些內容

AActor有3個管理組件的容器

• OwnedComponents：集合
• InstanceComponents：數組
• BlueprintCreatedComponents數組

另外還有一個重要的RootComponent組件

• 它是所有其它組件的根組件
• 它一定是USceneComponent類型即帶有變換的組件

private:
	TSet<UActorComponent*> OwnedComponents;
	UPROPERTY(Instanced)
	TArray<UActorComponent*> InstanceComponents;
public:
	UPROPERTY(TextExportTransient, NonTransactional)
	TArray<UActorComponent*> BlueprintCreatedComponents;
protected:
	UPROPERTY(BlueprintGetter=K2_GetRootComponent, Category="Utilities|Transformation")
	USceneComponent* RootComponent;
public:
	FORCEINLINE USceneComponent* GetRootComponent() const { return RootComponent; }

和場景中的AActor樹相關的一些內容

private:
	UPROPERTY(ReplicatedUsing=OnRep_Owner)
	AActor* Owner;
public:
	UPROPERTY(Transient)
	TArray<AActor*> Children;

	UFUNCTION(BlueprintCallable, Category=Actor)
	AActor* GetOwner() const;

	UFUNCTION(BlueprintCallable, Category=Actor)
	virtual void SetOwner( AActor* NewOwner );
	

和藍圖中的AActor樹相關的一些內容

	UFUNCTION(BlueprintCallable, Category="Actor")
	AActor* GetParentActor() const;

	UFUNCTION(BlueprintCallable, Category="Actor")
	UChildActorComponent* GetParentComponent() const;

一些奇葩的地方

• AActor應該是抽象層次很高的類，裏面竟然有關於傷害的定義
• 竟然還引用了子類APawn和ACharacter
• UInputComponent也應該是在APawn層級纔有交集

/**
	 * Whether this actor can take damage. Must be true for damage events (e.g. ReceiveDamage()) to be called.
	 * @see https://www.unrealengine.com/blog/damage-in-ue4
	 * @see TakeDamage(), ReceiveDamage()
	 */
	UPROPERTY(EditAnywhere, BlueprintReadWrite, SaveGame, Replicated, Category=Actor, meta=(AllowPrivateAccess="true"))
	uint8 bCanBeDamaged:1;
private:
	/** Pawn responsible for damage and other gameplay events caused by this actor. */
	UPROPERTY(BlueprintReadWrite, ReplicatedUsing=OnRep_Instigator, meta=(ExposeOnSpawn=true, AllowPrivateAccess=true), Category=Actor)
	class APawn* Instigator;
	UPROPERTY(DuplicateTransient)
	class UInputComponent* InputComponent;
	/**
	 * Return true if the given Pawn can be "based" on this actor (ie walk on it).
	 * @param Pawn - The pawn that wants to be based on this actor
	 */
	virtual bool CanBeBaseForCharacter(class APawn* Pawn) const;

	/**
	 * Apply damage to this actor.
	 * @see https://www.unrealengine.com/blog/damage-in-ue4
	 * @param DamageAmount		How much damage to apply
	 * @param DamageEvent		Data package that fully describes the damage received.
	 * @param EventInstigator	The Controller responsible for the damage.
	 * @param DamageCauser		The Actor that directly caused the damage (e.g. the projectile that exploded, the rock that landed on you)
	 * @return					The amount of damage actually applied.
	 */
	virtual float TakeDamage(float DamageAmount, struct FDamageEvent const& DamageEvent, class AController* EventInstigator, AActor* DamageCauser);

protected:
	virtual float InternalTakeRadialDamage(float Damage, struct FRadialDamageEvent const& RadialDamageEvent, class AController* EventInstigator, AActor* DamageCauser);
	virtual float InternalTakePointDamage(float Damage, struct FPointDamageEvent const& PointDamageEvent, class AController* EventInstigator, AActor* DamageCauser);