Unreal - Delegates and Events

Delegates And Events

Delegates and Events are simliar with different semantics.
- Delegates can be Broadcast by anyone where as events can only be broadcast by the owner
Only DYNAMIC_MULTICAST_DELEGATES can be accesed from Blueprints. Non dynamic delegates are event are code only forms
- This is due to the need to call the delgate by name
- DYNAMIC_MULTICAST_DELEGATES are said to be slower, which would makes sense considering the level of indirection needed to call from blueprint. Avoid use in pure code parts.
To be used in blueprint it is important to have the property BlueprintAssignable

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DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FHitByLaser, FLaserHit, LaserHit);
DECLARE_DYNAMIC_MULTICAST_DELEGATE(FLaserReceiverActivated);
DECLARE_DYNAMIC_MULTICAST_DELEGATE(FLaserReceiverDeactivated);
UCLASS(Blueprintable, ClassGroup=(Custom), meta=(BlueprintSpawnableComponent) )
class LASERFRIENDS_API ALaserReceiver : public AActor
{
    GENERATED_BODY()

public:	

    ... 

    UPROPERTY(BlueprintAssignable, Category = "Laser Receiver Events", Meta = (DisplayName = "Receiver Activated"))
    FLaserReceiverActivated LaserReceiverActivatedDelegate;

    UPROPERTY(BlueprintAssignable, Category = "Laser Receiver Events", Meta = (DisplayName = "Receiver Deativated"))
    FLaserReceiverDeactivated LaserReceiverDeactivatedDelegate;

    ...
}

When defining a struct as the argument it is important that the struct is also a BlueprintType if it is planned to be usable in blueprint

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USTRUCT(BlueprintType)
struct FLaserDestroyedBy {

    GENERATED_BODY()

    UPROPERTY(BlueprintReadOnly)
    ULaser* Laser;

    UPROPERTY(BlueprintReadOnly)
    AActor* DestroyedByActor;
};