Interface.md

2020-05-10_11:07:00

Interface

An interface is a set of functions. Other entities, such as an Actor, can implement the interface.

I'm unsure of how the UMyInterface and the IMyInterface interact in the examples below.

We can check for and call interface functions on an object in multiple ways in C++. First way:

if (MyActor->GetClass()->ImplementsInterface(UMyInterface::StaticClass()))
{
    IMyInterface::Execute_TestFunction(MyActor);
}

Second way:

if(IMyInterface* MyInterface = Cast<IMyInterface>(MyActor))
{
   MyInterface->TestFunction();
}

Third way:

if (MyActor && MyActor->Implements<UMyInterface>())
{
    IMyInterface::Execute_TestFunction(MyActor);
}

Forth way:

if (UKismetSystemLibrary::DoesImplementInterface(MyActor, UMyInterface::StaticClass()))
{
    IMyInterface::Execute_TestFunction(MyActor);
}

Some recommend the ImplementsInterface approach because it works for Blueprint implementations as well. I take that to mean that the Cast approach can't dispatch into a Blueprint Visual Script. Testing needed. Some recommend the Cast approach because it checks for nullptr. Some say that the Implements approach works on both C++ and Blueprint implementations. Some say that the UKismetSystemLibrary approach is the most robust. Unsure in what way.

Creating new interfaces

Blueprint

Right-click in the Content Browser > Blueprint > Blueprint Interface. Add function names with the Add Function button. These functions cannot have implementations, since this is just an interface. Add implementations in the Blueprint classes that implement the interface.

Add an interface to a Blueprint class in the class' Class Settings. Add interface function implementations in the Add Function part of the Blueprint Class Editor, but click Interface instead of the +.

[[2021-06-05_16:16:53]] Blueprint interface

C++

[[2020-03-10_21:29:17]] Actor
[[2021-06-05_16:16:53]] Blueprint interface