虚幻引擎 4：未调用 C++ 委托

Question

我一直致力于将一些蓝图逻辑转换为 C++。我有一个按钮。可以在 VR 中按下按钮，并调用一个委托来通知任何已注册的函数按下了按钮。下面是在 AButtonItem.h 类中声明委托的方式。

#pragma once
#include "BaseItem.h"
#include "ButtonItem.generated.h"

DECLARE_DYNAMIC_MULTICAST_DELEGATE(FButtonItemPressedSignatrue);

UCLASS()
class AButtonItem : public ABaseItem
{
    GENERATED_BODY()

protected:
    UPROPERTY(EditAnywhere, BlueprintReadOnly, Category = Touch)
    float myMaxButtonPress;

public:

    UPROPERTY(EditAnywhere, Category = Callback)
    FButtonItemPressedSignatrue ButtonItem_OnPressed;
};

当按下按钮时，代理的广播函数会被调用，如下所示：

ButtonItem_OnPressed.Broadcast();

（应该坚决调用这个函数，因为我有一个在调用之前打印的调试语句。同样重要的是要注意，当它是蓝图逻辑时，这一切都有效。）

这是我尝试向委托注册的地方以及我如何声明将被调用的函数：

WeaponMaker.h：

UFUNCTION()
void OnNextBladeButtonPressed();

WeaponMaker.cpp：

void AWeaponMaker::BeginPlay()
{
    Super::BeginPlay();

    TArray<USceneComponent*> weaponMakerComponents;
    this->GetRootComponent()->GetChildrenComponents(true, weaponMakerComponents);

    for (int componentIndex = 0; componentIndex < weaponMakerComponents.Num(); componentIndex++)
    {
        if (weaponMakerComponents[componentIndex]->GetName().Equals("NextBladeButton") == true)
        {
            myNextBladeButton = (AButtonItem*)weaponMakerComponents[componentIndex];
            break;
        }
    }

    if (myNextBladeButton != NULL)
    {
        myNextBladeButton->ButtonItem_OnPressed.AddDynamic(this, &AWeaponMaker::OnNextBladeButtonPressed);
    }

}

我在函数 OnNextBladeButtonPressed 中放置了一个断点和一个打印语句，所以我应该立即知道它什么时候工作，但它永远不会发生。我还从头开始重新创建了蓝图，但仍然没有运气。有时在编译时由于 InvocationList 无效而导致崩溃，但我也没有找到关于该问题的太多信息。底线是，OnNextBladeButtonPressed 没有被调用。

编辑：这是我在 AButtonItem 代码中调用广播函数的地方。因为我在控制台中看到 UE_LOG 输出，所以它似乎被调用了：

void AButtonItem::Tick(float deltaTime)
{
    FTransform buttonWorldTransform;
    FVector buttonLocalSpacePos;
    FVector ownerLocalSpacePos;
    FVector localDiff;
    float buttonPressAmount;

    if (myHasStarted == true)
    {
        Super::Tick(deltaTime);

        if (myButtonComponent != NULL)
        {
            if (myPrimaryHand != NULL)
            {
                //Get the world space location of the button.
                buttonWorldTransform = myButtonComponent->GetComponentTransform();

                //Convert the location of the button and the location of the hand to local space.
                buttonLocalSpacePos = buttonWorldTransform.InverseTransformPosition(myInitialOverlapPosition);
                ownerLocalSpacePos = buttonWorldTransform.InverseTransformPosition(myPrimaryHand->GetControllerLocation() + (myPrimaryHand->GetControllerRotation().Vector() * myPrimaryHand->GetReachDistance()));

                //Vector distance between button and hand in local space.
                localDiff = ownerLocalSpacePos - buttonLocalSpacePos;

                //Only interested in the z value difference.
                buttonPressAmount = FMath::Clamp(FMath::Abs(localDiff.Z), 0.0f, myMaxButtonPress);
                localDiff.Set(0.0f, 0.0f, buttonPressAmount);

                //Set the new relative position of button based on the hand and the start button position.
                myButtonComponent->SetRelativeLocation(myButtonInitialPosition - localDiff);

                //UE_LOG(LogTemp, Error, TEXT("buttonPressAmount:%f"), buttonPressAmount);
                if (buttonPressAmount >= myMaxButtonPress)
                {
                    if (myHasBeenTouchedOnce == false)
                    {
                        //Fire button pressed delegate
                        if (ButtonItem_OnPressed.IsBound() == true)
                        {
                            ButtonItem_OnPressed.Broadcast();
                            AsyncTask(ENamedThreads::GameThread, [=]()
                            {
                                ButtonItem_OnPressed.Broadcast();
                            });
                        }

                        myHasBeenTouchedOnce = true;
                        myButtonComponent->SetScalarParameterValueOnMaterials("State", 1.0f);
                        Super::VibrateTouchingHands(EVibrationType::VE_TOUCH);
                    }
                }
            }
            else
            {
                //Slowly reset the button position back to the initial position when not being touched.
                FVector newPosition = FMath::VInterpTo(myButtonComponent->GetRelativeTransform().GetLocation(), myButtonInitialPosition, deltaTime, 10.0f);
                myButtonComponent->SetRelativeLocation(newPosition);
            }
        }
    }
}

Answer 1

有时在编译时由于 InvocationList 无效而导致崩溃，但我也没有找到关于该问题的太多信息。底线是，OnNextBladeButtonPressed 没有被调用。

我在问题的代码中没有看到任何问题。在我看来，问题可能出在不同的位置。我怀疑 AWeaponMaker 在播放时已被删除。

Answer 2

首先：

UPROPERTY(EditAnywhere, Category = Callback)
FButtonItemPressedSignatrue ButtonItem_OnPressed;

这应该是：

UPROPERTY(BlueprintAssignable, Category = Callback)
FButtonItemPressedSignatrue ButtonItem_OnPressed;

为了方便。

其次，由于多种原因，可能会在开始播放之前调用 tick 函数。如果游戏尚未开始播放，您的事件将不会被播放。因此，为了避免在您的刻度功能中添加一个检查。

if(bHasBegunPlay)
{
  // .. your logics ...
}