Can't place UInterface and it's implementation class in one header?

Development Programming & Scripting UI
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1

I’m now meet a problem:

UINTERFACE(MinimalAPI,BlueprintType, meta = (CannotImplementInterfaceInBlueprint))
class UTestInterface : public UInterface
{
	GENERATED_BODY()
};

class TEST_API ITestInterface
{
	GENERATED_BODY()
};

UCLASS(NotBlueprintable, NotBlueprintType)
class TEST_API UTestInterfaceImpl : public UObject, public ITestInterface
{
GENERATED_BODY()
}

I place UTestInterface,UTestInterface and UTestInterfaceImpl in one header, and the UHT says:“error : Class ‘UTestInterface’ contains a dependency (#include or base class) to itself”,After I move UTestInterfaceImpl to another file,there have no error anymore.
At first, I think it is because UBT doesn’t allow to do this, but I find UHT allow the user to place multiple UCLASS declarations in one header.
So I’m confused. Why Multiple UClass is OK, but UInterface can’t do the same thing?

2

This has nothing to do for number of classes in file, it depency issue as error suggests, what are includes you making?

3

Nothing Special:
TestA.h:
#include “CoreMinimal.h”
#include “Interface.h”
#include “TestB.h”
#include “SubclassOf.h”
#include “TestA.generated.h”

TestB:
#include “CoreMinimal.h”
#include “UObject/Object.h”
#include “Classes/BlueprintJsonLibrary.h” //It’s a plugin’s header
#include “TestB.generated.h”

BlueprintJsonLibrary.h:
#include “CoreMinimal.h”
#include “Kismet/BlueprintFunctionLibrary.h”
#include “BlueprintJsonLibrary.generated.h”

error : Class ‘TestA’ contains a dependency (#include or base class) to itself

After I Move the declaration of TestAImpl to TestAImpl.h，It successfully compiled, I don’t even change any include in TestA.h(TestAImpl.h include TestA.h)

4

I need to use it in Blueprint,that is why I use UIneterface.

5

Hi Jack,

The error seems to go away for me if I delete UTestInterface. Do you need to interact with the interface from Blueprint, or are your implementations of the interface only for use by C++ (as in the case of UTestInterfaceImpl)?

6

Hi Jack,

I looked internally, and this bug has already been reported and is currently assigned to a developer. In the meantime, it seems like the only workaround is to split up the interface and the class that implements it.

7

I‘m glad to hear that. Thanks.