Interface problem in 4.16

Development Programming & Scripting C++
1

Hi,

I cannot get to compile my code, because I’m fighting with the Interface system.

The only difference in my method is that now I am using the “UnrealInterface” as the base class, instead of an empty class.

I only want to use the Interface in C++, so I would prefer not to mark my functions as BP Native or Implementable events.

I have created a test project to make things easier.
MyInterface: The Interface.
MyTriggerVolume: The Actor that calls the MyInterface function.
TargetActor: The Actor that implements MyInterface.

Here is my code:

MyInterface.h



#include "CoreMinimal.h"
#include "MyInterface.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI, meta = (CannotImplementInterfaceInBlueprint))
class UMyInterface : public UInterface
{
	GENERATED_BODY()
};


class INTERFACETEST_API IMyInterface
{
	GENERATED_BODY()

	// Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
	
	virtual void RunInterfaceTEST() = 0;
};

MyTriggerVolume.cpp



#include "MyTriggerVolume.h"
#include "MyInterface.h"

void AMyTriggerVolume::OnTiggerOverlap(AActor* InActor)
{
	IMyInterface* MyInterface = Cast<IMyInterface>(InActor);

	if (MyInterface != nullptr)
	{
		MyInterface->Execute_RunInterfaceTEST(InActor);
	}
}

TargetActor.h



#include "MyInterface.h"
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "TargetActor.generated.h"

UCLASS()
class INTERFACETEST_API ATargetActor : public AActor, public IMyInterface
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ATargetActor();

	virtual void RunInterfaceTEST() override;
};

TargetActor.cpp



void ATargetActor::RunInterfaceTEST_Implementation()
{

}

Compile Error message:



\Documents\Unreal Projects\InterfaceTEST\Source\InterfaceTEST\MyTriggerVolume.cpp(21): error C2039: 'Execute_RunInterfaceTEST': is not a member of 'IMyInterface'
\documents\unreal projects\interfacetest\source\interfacetest\MyInterface.h(19): note: see declaration of 'IMyInterface'
\Documents\Unreal Projects\InterfaceTEST\Source\InterfaceTEST\TargetActor.cpp(15): error C2039: 'RunInterfaceTEST_Implementation': is not a member of 'ATargetActor'
\documents\unreal projects\interfacetest\source\interfacetest\TargetActor.h(11): note: see declaration of 'ATargetActor'
1>ERROR : UBT error : Failed to produce item: \Documents\Unreal Projects\InterfaceTEST\Binaries\Win64\UE4Editor-InterfaceTEST.pdb
1>  Total build time: 17.16 seconds (Local executor: 0.00 seconds)
1>C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.MakeFile.Targets(41,5): error MSB3075: The command ""C:\Program Files\Epic Games\UE_4.16\Engine\Build\BatchFiles\Build.bat" InterfaceTESTEditor Win64 Development "\Documents\Unreal Projects\InterfaceTEST\InterfaceTEST.uproject" -waitmutex" exited with code 5. Please verify that you have sufficient rights to run this command.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

I have tried several other solutions found on the net, but apparently none of them worked.

At this point I would ask if anyone knows the correct way to create, implement and call a C++ only interface?

Thanks!

2

This is how you should execute interface methods:

if (InActor->Implements<UMyInterface>())
{
IMyInterface::Execute_RunInterfaceTEST(InActor);
}

3

Hi Iceey,

Thanks for your solution, I have never seen this Implements check before. Are you sure that the casting I have used is incorrect? It was working well before 4.16.

Unfortunately, changing the interface calling method produces the same error :frowning:

I have never had a problem with interfaces before, and it is driving me crazy now. Is it even possible to work with the UnrealInterface derived interface?

Any input would be really appreciated!

4

Sorry to hear that it didn’t work. I always create my interfaces through the editor by clicking Add new c++ class. My interfaces are purely virtual and I overwrite the behaviour in C++ class aswell as derrived BP Here’s a sample so you can copy it:
I also noticed that you use GENERATED_BODY(). Try using GENERATED_UINTERFACE_BODY() aswell as GENERATED_IINTERFACE_BODY(). Hope it helps


#pragma once

#include "InterfaceInventory.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI)
class UInterfaceInventory : public UInterface
{
	GENERATED_UINTERFACE_BODY()
};

/**
 * 
 */
class AOH_API IInterfaceInventory
{
	GENERATED_IINTERFACE_BODY()

	// Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
	UFUNCTION(BlueprintNativeEvent, BlueprintCallable, Category = "Ownership")
		void OnChange_ItemArray();
	
};




#include "InterfaceInventory.h"


// This function does not need to be modified.
UInterfaceInventory::UInterfaceInventory(const class FObjectInitializer& ObjectInitializer)
: Super(ObjectInitializer)
{
}

// Add default functionality here for any IInterfaceInventory functions that are not pure virtual.

Then in C++ base class:


#include "InterfaceInventory.h"

UCLASS()
class AOH_API ADefaultMapCharacter : 
	public ACharacter,
	public IInterfaceInventory
{
	GENERATED_BODY()

	UFUNCTION(BlueprintNativeEvent, BlueprintCallable, Category = "Character Properties")
		void OnChange_ItemArray();
	virtual void OnChange_ItemArray_Implementation() override;

}



void ADefaultMapCharacter::OnChange_ItemArray_Implementation()
{

}

I do Implements checks to inform my log that some actor didn’t declare it’s behaviour. My system is based on Component <-> Interface combination. Some of my components also require their Interfaces to be implemented too. Saves a lot of time debugging.

5

Thanks Iceey, I will be soon able to test it out!

I noticed that macro difference too, but this is what Unreal has generated. There is a class called UnrealInterface that you can inherit from (using the Editor’s AddClass tab), and I was able to use it with BlueprintNative events. However I want to use pure virtual functions this time, but I cannot get them to compile. I guess I will stick to the “traditional” interface creation method, instead of this new class.

Thanks again!

6

Okay, I finally got it to working, thank you so much for your help Iceey!

I managed to used the UnrealInterface class, here is what I had to change based on my original post, if anyone is interested.

MyInterface.h



#include "CoreMinimal.h"
#include "MyInterface.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI)
class UMyInterface : public UInterface
{
	GENERATED_BODY()
};


class INTERFACETEST_API IMyInterface
{
	GENERATED_BODY()

	// Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
	
        UFUNCTION(BlueprintNativeEvent)
	void RunInterfaceTEST();
};

MyTargetActor.h



#include "MyInterface.h"
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "TargetActor.generated.h"

UCLASS()
class INTERFACETEST_API ATargetActor : public AActor, public IMyInterface
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ATargetActor();

	virtual void RunInterfaceTEST_Implementation();
};

The weird thing is that the IMyInterface::Execute_ method was crashing the game, so I had to use my original solution.

That was it, I never did, and would have thought about using _Implementation in the .h declaration, so thank you so much again, Iceey!

7

No problem. Glad I could help.