Issue with override c++ function with blueprint

Development Programming & Scripting
1

hi all, i have some issue when i trying to override my c++ function with blueprint.

i have a class A.h :

UFUNCTION(BlueprintNativeEvent)
		void OnPickedUp();

and A.cpp :

void APickup::OnPickedUp_Implementation()
{
	// there is no default behavior to the item when it is picked up 
}

and a class B, a child of classe A ( class B : public A )

B.h :

void OnPickedUp_Implementation() override;

B.cpp :

void ACoin::OnPickedUp_Implementation()
{
	//call the parent implementation first
	Super::OnPickedUp_Implementation();

	if (GEngine)
	{
		FString test = "its works";
		GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Red, test);
	}

	/* Destroy the Coin */
	Destroy();

}

and my blueprint :

15037-bp_issue.png
15037-bp_issue.png1152×648 67.5 KB

when i pickup a item , the function OnPickUp is called , the item is detroy and a message appear in the game . but the blueprint override is not call.
if i make a link between "Event Destroy"and “Play sound at location”, this work so is not a blueprint probleme.

What i do wrong ?

Thanks

2

I Have found there is a certain methodology to the madness when it comes to using UE4. Because of the layers of indirection between the C++ code you write, the the C++ code generated by the UBT, to the way blueprints implement things can get a bit confusing. The first and foremost is I do not think your PickedUp_Implemented is marked virtual in your A.h class and I don’t think you can mark it virtual either. This is most likely why your changes are not being called.

How I would solve this is to create a function in your base class A.h

 UFUNCTION(BlueprintCallable)
         virtual void PickedUp();

UFUNCTION(BlueprintNativeEvent)
    OnPickedUp();

The make your implementation function in A.cpp

void A::PickedUp()
{
    OnPickedUp();
}

void A::OnPickedUp_Implementation()
{
    // do something
}

Now if you need to implement something new in C++ in your B class you can override the PickedUp function.

B.h

virtual void PickedUp() override;

implementation

void B::PickedUp()
{
    // Do Custom Stuff here
    // Call Super::PickedUp()
    // Or do custom stuff here
    // Or forget Super and just call OnPickedUp() it's protected after all
}
3

this work fine, tanks !

4

I have a bit of an Update to this, while this method works you may be able to specify that a Function_Implementation is virtual afterall. I stumbled across a UFunction specifier called CustomThunk Through some random sequence of events I learned that UE4 calls the generated _implementation functions “thunks”. Unfortunately I do not know more than this but figured it may be useful to you to play round with.

5

Function void A::OnPickedUp(); is virtual. If it wasn’t
void B::OnPickedUp_Implementation() override; would not compile as You cannot override non virtual functions