Unreal has two UFUNCTION() specifiers that allow C++ to call functions whose behaviour is defined in Blueprint subclasses: BlueprintImplementableEvent and BlueprintNativeEvent.
At first glance they look kind of like the same thing, BlueprintImplementableEvent
The Basics
BlueprintImplementableEvent | BlueprintNativeEvent | |
|---|---|---|
| Define function behaviour in Blueprints | ✅ | ✅ |
| Define function behaviour in parent C++ | ❌ | ✅ |
Implementable Event
// In .h
UFUNCTION(BlueprintImplementableEvent)
void PlantFlowers(const FGameplayTag& FlowerTag, const FLinearColor& Color, int32 Count);
Garden_NativeEvent.h
// In .h
UFUNCTION(BlueprintNativeEvent)
void PlantFlowers(const FGameplayTag& FlowerTag, const FLinearColor& Color, int32 Count);
// In .cpp
void UGarden::PlantFlowers_Implementation(const FGameplayTag& FlowerTag, const FLinearColor& Color, int32 Count)
{
}
However there is a well-used paradigm in the engine for creating BlueprintImplementableEvent functions that do have a base C++ behaviour
Garden_NativeEvent.h
UCLASS()
vs
```cpp
// .h
UFUNCTION(BlueprintNativeEvent)
void DoSomething();
// .cpp
void UMyClass::DoSomething_Implementation()
{
}
Blueprints can easily forget to call parent C++
Unless you're using Blueprint Assist, overriding a BlueprintNativeEvent function in Blueprints does not automatically add a call to the parent function.
Users have to remember to right-click the newly-created function node and click "Add Call to Parent". This is very easy to forget to do.
- Blueprint users can choose whether to call, and when to call the parent C++ function.
- Blueprint users can easily forget to call the parent C++ function
- Adding new parameters to the function requires them to be manually hooked up in every Blueprint that implements that function
New Parameters Are Not Connected to Parent Call
Imagine you have a BlueprintNativeEvent function, and it's being overridden in a lot of Blueprint subclasses. Imagine you want to add a new parameter to that function, and use it in your _Implementation C++ function.
From a Blueprint perspective they are very similar kkk
