How to swap components within PostEditChangeProperty

Development Programming & Scripting C++
1

hi,

i’m new to unreal engine (coming from unity). just trying to create some simple item pickup system.
therefore i created a pickup base class with a UStaticMeshComponent as RootComponent and a UShapeComponent as the trigger.
now i want to accomplish that i can select what type of UShapeComponent i like to use.
so i defined an enum with my possible shape values. then in PostEditChangeProperty i check if the TriggerShape has been changed and if so
i create a new Trigger and attach it to my root component.

then i create a blueprint based on my pickup. when i change now the value in the blueprint editor… the unreal editor crashes.

what am i doing wrong? or how should i implement the behaviour i like to achieve?



// Header
UENUM(BlueprintType)
enum class ETriggerShape : uint8
{
	S_Box		UMETA(DisplayName = "Box"),
	S_Sphere	        UMETA(DisplayName = "Sphere"),
	S_Max		UMETA(Hidden)
};

UCLASS()
class APickup : public AActor
{
	GENERATED_BODY()
	
public:	
	APickup();

	UPROPERTY(EditDefaultsOnly, BlueprintReadWrite, Category = "Pickup")
	ETriggerShape TriggerShape;

protected:
	UPROPERTY(VisibleDefaultsOnly, BlueprintReadOnly, Category = "Pickup")
	class  UShapeComponent* Trigger;

	UPROPERTY(VisibleDefaultsOnly, BlueprintReadOnly, Category = "Pickup")
	class  UStaticMeshComponent* Mesh;

private:
	virtual void PostEditChangeProperty(struct FPropertyChangedEvent& PropertyChangedEvent) override;
};

// Cpp
APickup::APickup()
{
	PrimaryActorTick.bCanEverTick = false;

    Mesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Mesh"));
    RootComponent = Mesh;

    Trigger = CreateDefaultSubobject<UBoxComponent>(TEXT("Trigger"));
    Trigger->AttachTo(RootComponent);
}

void APickup::PostEditChangeProperty(struct FPropertyChangedEvent& PropertyChangedEvent)
{
    FName propertyName = (PropertyChangedEvent.Property != nullptr) ? PropertyChangedEvent.Property->GetFName() : NAME_None;

    if (propertyName == GET_MEMBER_NAME_CHECKED(APickup, TriggerShape))
    {
        Trigger->DetachFromParent();
        Trigger->DestroyComponent();

        if (TriggerShape == ETriggerShape::S_Box)
            Trigger = NewObject<UBoxComponent>(this, TEXT("Trigger"));
        else
            Trigger = NewObject<USphereComponent>(this, TEXT("Trigger"));

        Trigger->AttachTo(RootComponent);
    }

    Super::PostEditChangeProperty(PropertyChangedEvent);
}
2

Also it´s an old Post: as your Trigger is of type UShapeComponent you first need to to Cast to the needed component type:
I tried to do exactly this and so I stumbled upon this post. I do something like this:



switch (CustomTriggerShape)
    {
        case ECustomTriggerShapes::none:
            UE_LOG(LogTemp, Log, TEXT("Do NONEThings"));
            break;
        case ECustomTriggerShapes::BoxTrigger:
            UE_LOG(LogTemp,Log, TEXT("Do BOXThings"));
            HazardTrigger = Cast<UBoxComponent>(NewObject<UBoxComponent>(this));
            break;
        case ECustomTriggerShapes::SphereTrigger:
            UE_LOG(LogTemp,Log, TEXT("Do SPHEREThings"));
            HazardTrigger = Cast<USphereComponent>(NewObject<USphereComponent>(this));
            break;
        case ECustomTriggerShapes::CapsuleTrigger:
            UE_LOG(LogTemp,Log, TEXT("Do CAPSULEThings"));
            HazardTrigger = Cast<UCapsuleComponent>(NewObject<UCapsuleComponent>(this));
            break;
    }

But the DetailsPanel itself does not Refresh this time. You need to to reselect the Object in the worldOutliner to refresh the state of the Object.

3

It probably crashes because the addition of a component calls posteditchangeproperty? just a guess.

4

I have also meet the same problem before. the reason why editor crashed probably is that you use the same name to new a object(Trigger = NewObject(this, TEXT(“Trigger”)):wink: