UInputComponent BindAction variadic

Development Programming & Scripting
1

Hi, I’m trying to bind input to my pawn and following along a tutorial I use:

   // get input component
	inputComponent = GetOwner()->FindComponentByClass<UInputComponent>();
	if (inputComponent)
	{
		UE_LOG(LogTemp, Warning, TEXT("input component present in %s."), *GetOwner()->GetName())
		
		inputComponent->BindAction("grab", EInputEvent::IE_Pressed, this, &UGrabber::Grab);
	}
	else
		UE_LOG(LogTemp, Error, TEXT("input component missing in %s."), *GetOwner()->GetName())

I noticed that BindAction has a variadic overload that takes parameters, so I guessed it allows me to pass parameter to a delegate:

typedef void(UGrabber::*Delegate)(int);
    		inputComponent->BindAction<Delegate, UGrabber>("grab", EInputEvent::IE_Pressed, this, &UGrabber::GrabWithParams, 10);   // this doesn't work

it needs the call signature of the delegate, but this does not compile. Why?

2

The reason that your function doesn’t work out of the box is that the function signature has to be defined. Note that the variadic variant of this function also requires a template type Delegate.

If you look at the InputComponent header you’ll find that the full signature of the non-variadic version looks like this.

template< class UserClass > FInputActionBinding& BindAction( const FName ActionName, const EInputEvent KeyEvent, UserClass* Object, typename FInputActionHandlerSignature::TUObjectMethodDelegate< UserClass >::FMethodPtr Func )

Note the “typename FInputActionHandlerSignature” part. This is a typedef for TDelegate

The variadic version looks like this:

template< class DelegateType, class UserClass, typename… VarTypes >
FInputActionBinding& BindAction( const FName ActionName, const EInputEvent KeyEvent, UserClass* Object, typename DelegateType::template TUObjectMethodDelegate< UserClass >::FMethodPtr Func, VarTypes… Vars )

It expects a type that has a template member with the name TUObjectMethodDelegate. Although you could make your class that has such a member template, in most every case you’d want to call the variadic version like so:

InputComponent->BindAction < TDelegate < void(int) >, UGrabber >(TEXT("Grab"), EInputEvent::IE_Pressed, this, &UGrabber::Grab, 10);

Your question is almost two years old, but who knows, maybe it’s still useful to you. I hope it will at least be for the next visitors with the same question.

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