Variables in Unreal c++ Interfaces not showing up in blueprint

Development Programming & Scripting Blueprint
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1

Hi! I’m trying out interfaces in Unreal c++ and seeing what I can do with them.

My setup right now is really simple:

I have a blueprint class: TemporaryBlueprint
TemporaryBlueprint is a child of ATemporaryActor (c++ class)
ATemporaryActor is a child of Actor, and IMyInterface (c++ class)

MyInterface.h

#pragma once

#include "CoreMinimal.h"
#include "UObject/Interface.h"
#include "MyInterface.generated.h"

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

/**
 * 
 */
class DEVSPACE_API IMyInterface
{
	GENERATED_BODY()

	// Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "From|Interface")
		bool TestEvent();

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "From|Interface", meta = (AllowPrivateAccess = "true"))
		bool InterfaceVariable;
};

TemporaryActor.h:

#pragma once

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

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

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

protected:
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "From|Child", meta = (AllowPrivateAccess = "true"))
		bool abcd;
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "From|Child", meta = (AllowPrivateAccess = "true"))
		bool efgh;
};

The blueprint class does show every variable from ATemporaryActor, but not from IMyInterface.

Is this impossible, or am I missing something?

2

i think you need to do it like this :

UINTERFACE(MinimalAPI, Blueprintable)

1 Like
3

I don’t beleive they can have properties. That is not their function. An Interface’s role is to enforce function implementation on the class that implements them.

Put your properties in a base class and use inheritence, if you want specific uproperties in a class.

1 Like
4

This sounds like it should work but sadly doesn’t.

5

Dang, I suspected as much.
I just now found this thread that seems to confirm it: Member Variable Declaration not allowed in Interfaces?

Thanks btw! I’ll tinker around and see what solution I’ll come up with.

6

Just add getter/setter functions

protected:
    bool abcd;
public:
    UFUNCTION(BlueprintCallable, BlueprintNativeEvent)
    bool GetAbcd();
    virtual bool GetAbcd_Implementation() { return abcd; }
    UFUNCTION(BlueprintCallable, BlueprintNativeEvent)
    void SetAbcd(bool b);
    virtual void SetAbcd_Implementation(bool b) { abcd = b; }
7

This will not work if you implement the interface in Blueprint for two reasons:

  1. The variable will not be part of the Blueprint Generated Class
  2. Default UFUNCTION event implementations will not ever be called.
8

True, but it works just fine if you implement interface in C++ class.

You can even override the BlueprintNativeEvents in BP child classes, and use “call parent function” from there, so you can add BP logic to the setter.

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