Event Processors

An Event Processor is a function that is assigned to an I/O event. This function is always triggered before an action (that's bound to this event) is executed.

These event processor functions are used when your event has parameters, and you want to expose them as Named Arguments for actions to use.

The event processor can also be used to abort I/O action execution in case that particular I/O event should not always fire with the underlying delegate. For example the actor's EndPlay delegate is called for multiple reasons, but we might only want to actually react to it if the reason is due to the actor being destroyed.

Usage Example

Let's say you have an event called OnPickup. You can create a new function and assign it as the event processor of the OnPickup event. Make sure that the parameter list of the function matches the delegate exactly. In my case this is a Blueprint event dispatcher with one variable for the pawn that picked up the item, so my event processor also has that one parameter.

On the left you can see the function I created, and on the right is where the I/O event is registered.

Inside the event processor, simply use the SetNamedArgument function to add a new named argument to the current execution context. Notice that the value of the argument is still in string form, so it must be in the format that is understood by the I/O system and Unreal. See Function Parameters section for more details.

void APickupActor::ProcessEvent_OnPickup(APawn* InstigatorPawn)
{
	FActionExecutionContext& ExecContext = FActionExecutionContext::Get(this);
	ExecContext.SetNamedArgument(TEXT("$Instigator"), InstigatorPawn->GetPathName());
}