虚幻引擎4：未调用C ++委托

Question

I've been working on converting some blueprint logic over to C++. One of the things I have is a button. The button can be pressed in VR and has a delegate that is called to notify any registered functions that the button press occurred. Here is how the delegate is declared in the AButtonItem.h class.

#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;
};

The delegate's broadcast function is then being called when the button is pressed like so:

ButtonItem_OnPressed.Broadcast();

(This function should defiantly be called because I have a debug statement that prints right before the call. Its also important to note this was all working when it was blueprint logic.)

Here is where I try to register with the delegate and how I declared the function that will be called:

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);
    }

}

I put a breakpoint and a print statement in the function OnNextBladeButtonPressed so I should immediately know when it works but its never happening. I also re-created the blueprint itself from scratch but still no luck. Sometimes on compile I get a crash due to the InvocationList being invalid but I haven't found much info on that issue either. Bottom line is, OnNextBladeButtonPressed is not getting called when it should be.

Edit: Here is where I call the broadcast function in my AButtonItem code. It seems to be getting called since i see the UE_LOG output in the console:

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

First of all:

UPROPERTY(EditAnywhere, Category = Callback)
FButtonItemPressedSignatrue ButtonItem_OnPressed;

This should be:

UPROPERTY(BlueprintAssignable, Category = Callback)
FButtonItemPressedSignatrue ButtonItem_OnPressed;

For convenience.

Secondly the tick function may be called before begin play is executed for a number of reasons. Your even't won't be broadcasted if the game hasn't begin play yet. So to avoid just add a check in your tick function.

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

Answer 2

Sometimes on compile I get a crash due to the InvocationList being invalid but I haven't found much info on that issue either. Bottom line is, OnNextBladeButtonPressed is not getting called when it should be.

I don't see any issue in the code from the question. At my glance, the issue could be in different location. I would suspect that AWeaponMaker had been deleted at moment of broadcasting.