Calling delegate fails in Blueprint implemented event from C++

Development Programming & Scripting C++
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1

Hi, for a project I have made a base-class (BouncingPadManager) in C++.

This base class is spawned and managed by the game mode.

#pragma once

// ...includes here

UCLASS()
class GAMEPROJECT_API ABouncePadManager : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	UFUNCTION(BlueprintImplementableEvent, Category="Events")
	void OnScoreEvent(FTeamScore nativeSide, FTeamScore invaderSide); // no implementation in cpp

	UFUNCTION(BlueprintImplementableEvent, Category="Events")
	void OnGameEnd(); // no implementation in cpp
// ...here be more stuff
};

When a player scores this event gets called in the gamemode.

void ASportGamemode::AddScore(ETeams team, int point)
{
	// Notify BouncingPadManager
	BouncingPadManager->OnScoreEvent(nativeScore, invaderScore);
}

Now onto the weird part:
My BP_BouncingPadManager that derives from BouncingPadManager.cpp works on the following ways:

In begin play the delegate works fine and the output is as expected.

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image1127Ă—515 73.9 KB

In tick the delegate also broadcasts fine and the output is as expected.

In the implemented OnScoreEvent (from the base c++ class) the delegate never calls anything so no output/desired behavior is produced. Any other code besides the delegates works fine(parameters were disconnected to simplify example.)

image
image1104Ă—378 73 KB

My question is: Why? and how can this be fixed.

2

Have you tried putting in a break point on OnScoreEvent? Is it being triggered?

Do you have c++ implementation code for OnScoreEvent?

  • OnScoreEvent_Implementation(FTeamScore nativeSide, FTeamScore invaderSide);

if so does it trigger?

3

A breakpoint in OnScoreEvent gets triggered, the C++ Doesn’t have an implementation so no nothing triggers. I have tried adding an implementation but the compiler won’t except it.

Error: BouncePadManager.cpp.obj : error LNK2005: "public: void __cdecl ABouncePadManager::OnScoreEvent(struct FTeamScore,struct FTeamScore)" (?OnScoreEvent@ABouncePadManager@@QEAAXUFTeamScore@@0@Z) already defined in BouncePadManager.gen.cpp.obj

I have found a way around the problem by just directly calling the function on a bouncing pad instead, but I just wish to know the reason why my initial approach didn’t work.

image

4

You should have it like this in the header

UFUNCTION(BlueprintCallable, BlueprintImplementableEvent)
		void OnScoreEvent(struct FTeamScore,struct FTeamScore);
	virtual void OnScoreEvent_Implementation(struct FTeamScore,struct FTeamScore);

then in the cpp

void ABouncePadManager::CalculateStatsBP_Implementation() {
// your code here
}

then from c++ try calling

	BouncingPadManager->OnScoreEvent_Implementation(nativeScore, invaderScore);

The virtual function is the one that can be overridden in blueprints.

5

I have tried to add these lines

image

void ASportGamemode::AddScore(ETeams team, int point)
{
	// Notify BouncingPadManager
	BouncingPadManager->OnScoreEvent_Implementation(nativeScore, invaderScore);
}

image

But now the compiler doesn’t want to compile it.

7

Your second parameter us not a struct, it’s an int.

Are the structs defined a unreal ustructs?

8

The parameters are right, I removed redundant code to show the problem. NativeScore and Invaderscore are of the correct datatype.

And somehow it works now, even though I have reverted everything to its original state.

Ill be closing this issue.

1 Like
9

It has to be a BlueprintNativeEvent so it can have a base C++ implementation, the BlueprintImplementableEvent doesn’t