UE4 C++与蓝图的继承问题

C++写了一个类MyChar，并派生了一个蓝图子类BP_MyCharacter。

// Fill out your copyright notice in the Description page of Project Settings.#pragma once#include "CoreMinimal.h" #include "GameFramework/Character.h" #include "MyCharacter.generated.h"using namespace UP; using namespace UF;UCLASS() class CPPTEST_API AMyCharacter : public ACharacter {GENERATED_BODY()public:// Sets default values for this character's propertiesAMyCharacter();protected:// Called when the game starts or when spawnedvirtual void BeginPlay() override;public: // Called every framevirtual void Tick(float DeltaTime) override;// Called to bind functionality to inputvirtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;UPROPERTY(VisibleAnywhere)class UCameraComponent* fpsCamera;};// Fill out your copyright notice in the Description page of Project Settings.#include "MyCharacter.h" #include <Camera/CameraComponent.h>// Sets default values AMyCharacter::AMyCharacter() {// Set this character to call Tick() every frame. You can turn this off to improve performance if you don't need it.PrimaryActorTick.bCanEverTick = true;fpsCamera = CreateDefaultSubobject<UCameraComponent>(TEXT("FpsCamera"));//fpsCamera->SetupAttachment(RootComponent);//fpsCamera->SetRelativeLocation(FVector(0, 110, 0));}// Called when the game starts or when spawned void AMyCharacter::BeginPlay() {Super::BeginPlay();auto info = FString::Printf(TEXT("-11mychar,inst:%d"), this);GEngine->AddOnScreenDebugMessage(-1, 21, FColor::Red, info);}// Called every frame void AMyCharacter::Tick(float DeltaTime) {Super::Tick(DeltaTime);}// Called to bind functionality to input void AMyCharacter::SetupPlayerInputComponent(UInputComponent* PlayerInputComponent) {Super::SetupPlayerInputComponent(PlayerInputComponent);}

实验一，做如下操作：

1，修改蓝图中的fpsCamra的位置，任意，如世界空间位置(0,0,200)

2，注释掉构造函数中的fpsCamera的创建代码，并编译。这时fpsCamera在蓝图中消失了。

AMyCharacter::AMyCharacter() {// Set this character to call Tick() every frame. You can turn this off to improve performance if you don't need it.PrimaryActorTick.bCanEverTick = true;//fpsCamera = CreateDefaultSubobject<UCameraComponent>(TEXT("FpsCamera"));//fpsCamera->SetupAttachment(RootComponent);//fpsCamera->SetRelativeLocation(FVector(0, 110, 0));}

3，恢复构造函数中的fpsCamera的创建代码，并编译，这时fpsCamera在蓝图中又出现了。但位置被重置为世界空间的(0,0,0)。原因是2，3两步相当于先删除了相机组件再新加了一个相机组件，所有数据都是默认的了。但如果步2不删除相机组件，而仅修改相机位置，编译后发现蓝图中相机位置是没有任何改变的，原因是构造函数执行时先执行父类构造再执行蓝图子类构造，这样C++构造函数中的位置修被蓝图中的位置修改覆盖掉了。

这时候资源浏览器中BP_MyCharacter并没有带星号，也就是说UE编译器没有监视到蓝图的数据发生了改变。

AMyCharacter::AMyCharacter() {// Set this character to call Tick() every frame. You can turn this off to improve performance if you don't need it.PrimaryActorTick.bCanEverTick = true;fpsCamera = CreateDefaultSubobject<UCameraComponent>(TEXT("FpsCamera"));//fpsCamera->SetupAttachment(RootComponent);//fpsCamera->SetRelativeLocation(FVector(0, 110, 0));}

4，关闭UE4，不主动保存蓝图。重新打开UE4，打开BP_MyCharacter，发现fpsCamera的位置是世界空间的(0,0,200)。而如果关闭UE4之前，主动保存一下蓝图，再打开UE4，打开蓝图，发现fpsCamera的位置是世界空间的(0,0,0)

总结，此问题的关键三要素是：父类内存，子类内存，磁盘数据。

总结

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