Broadcasting and Subscribe in C++

C++ code

Add to QuestMarker.h

protected:
    virtual void BeginPlay() override;

private:
    void QuestUpdate(int32 Index);

Added to QuestMarker.cpp

void AQuestMarker::BeginPlay()
{
    GetQuestManager()->CompletedQuest.AddDynamic(this, &AQuestMarker::QuestUpdate);
    RefreshVisibility();
}

void AQuestMarker::QuestUpdate(int32 Index)
{
    RefreshVisibility();
}

Add one line at the bottom of QuestManager.cpp -> AQuestManager::CompleteQuest_Implementation

CompletedQuest.Broadcast(QuestIndex);

Blueprint

We can not delete the event graph for QuestMarker and QuestManager