Interfaces And Blueprints - Epic Wiki
# Interfaces And Blueprints
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Template:Rating Using interfaces with C++ and Blueprints can be a little tricky when the interface is implemented purely in Blueprints. Currently, when a Blueprint implements an Interface the C++ InterfaceCast<> type cast does not work.
Interface Cast Method
// Other code
}
What you need to do instead is:
(Originally discovered by Lion032, source)
Implements Interface Method
// Other code
}
This will work for both C++ implemented interfaces and Blueprint implemented interfaces. From here, you can use the static Execute versions of the interface functions.
Header:
GENERATED_UINTERFACE_BODY()
};
class IMyInterface {
GENERATED_IINTERFACE_BODY()
public:
UFUNCTION(BlueprintImplementableEvent) void MyInterfaceFunction();
};
Interface function example:
IMyInterface::Execute_MyInterfaceFunction(ActorInstance);
}
It is likely that the static Execute functions are generated by the Unreal Header Tool (UHT) only for interface functions that declare UFUNCTION(). This means that you can't make a virtual interface function which uses UFUNCTION() and intellisense won't pick them up.
# More Complete Example (Passing Self as Reference):
MyInterface.H:
class AMyActor;
UINTERFACE(Category = "My Interface", BlueprintType, meta = (DisplayName = "My Interface")) class MYMODULE_API UMyInterface : public UInterface { GENERATED_UINTERFACE_BODY() };
class MYMODULE_API IMyInterface { GENERATED_IINTERFACE_BODY() public: /// My Initialization Interface. UFUNCTION(Category = "My Interface", BlueprintNativeEvent, BlueprintCallable, meta = (DisplayName = "On My Interface Execute") void OnInitialized(const AMyActor* Context); };
MyActor.H:
MyActor.CPP:
void AMyActor::OnInitialized_Implementation(const AMyActor* Context) {
if (Context != this) {return;}
TArray<AActor*>Interfaces; // Pick only Actors with Interface, instead of iterating whole World: UGameplayStatics::GetAllActorsWithInterface(this,UMyInterface::StaticClass(),Interfaces);
for (const auto &Actor : Interfaces) {
// Try to Execute on C++ layer: const auto &Interface = Cast
// Else, Execute Interface on Blueprint layer instead: if (Actor->GetClass()->ImplementsInterface(UMyInterface::StaticClass())) { IMyInterface::Execute_OnInitialized(Actor,Context); }
}
}
void AMyActor::BeginPlay() { Super::BeginPlay();
// Fire off the Native Event, which is going to be received by all the other Actors: Execute_OnInitialized(this,this);
}
Notes: Example above is implemented with old GENERATED_UCLASS_BODY() instead of new GENERATED_BODY() one. If you want your Actor to receive C++ Interface calls instead of from Blueprint layer, your Actor must inherit from both AActor class and your Interface class, like so:
# Update and pointer to more detailed discussion
Thanks for this wiki; I think it is essential on getting interfaces to work properly. I wrote a longer discussion of what I think is going on with Blueprint and C++ interfaces at https://answers.unrealengine.com/questions/214147/grand-unified-cblueprint-cast-interface-explanatio.html which I thought readers of this topic might find useful. -Xarol
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