How do I pass a Tarray in a BlueprintImplementableEvent?

Development Programming & Scripting Blueprint
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1

I want to dispatch this event in several cases and handle all of them in same node and its connecting logic. Works fine for primitives like float but for a tarray of a struct (stack of inventory items), it screams this error.

UFUNCTION(exec, BlueprintImplementableEvent, Category = "ServerManager")
virtual void OnItemsUpdate(TArray<FItemStack> ItemList);

Error	1	error C2511: 'void AServerManager::OnItemsUpdate(const TArray<FItemStack,FDefaultAllocator> &)' : overloaded member function not found in 'AServerManager'	D:\UE4\Prototype\Intermediate\Build\Win64\Inc\Prototype\Prototype.generated.cpp	205
Error	2	error C2352: 'UObject::FindFunctionChecked' : illegal call of non-static member function	D:\UE4\Prototype\Intermediate\Build\Win64\Inc\Prototype\Prototype.generated.cpp	208

And

USTRUCT(BlueprintType)
struct PROTOTYPE_API FItemStack
{
	GENERATED_USTRUCT_BODY()

In case it mattered what that type was.

Any ideas what I am doing wrong? Thanks in advance!

2

You should have your tarray as a const with a & at the end, something like this:

MyFunction(const TArray<AActor*>& VarName)
5 Likes
3

Could you briefly explain why this needs to be done? Or direct me to an article or something that explains it? Thanks

4

Error C2511 is returned when you try to implement a function that does not exist (a very basic example can be found at c++ - VS2010 overloaded member function not found - Stack Overflow). Somewhere in your code you have an implementation of the function

    void AServerManager::OnItemsUpdate(const TArray<FItemStack,FDefaultAllocator> &)

Which does not exist. The virtual function you need to implement is

    virtual void OnItemsUpdate(TArray<FItemStack> ItemList)

I cant tell much because not much info on your declarations and implementations has been posted but changing your implementation line to this should fix it

    void AServerManager::OnItemsUpdate(TArray<FItemStack> ItemList)

The 2 differences are

  1. virtual function does not have want a “const TArray”
  2. virtual function takes an object not a reference (&)

To save any confusion, your implementation line will not actually have

    TArray<FItemStack,FDefaultAllocator>

it will have

    TArray<FItemStack>

The FDefaultAllocator is something that would be added by the C++ compiler

As for error C2352, i cant tell what is happening here because i dont know what FindFunctionChecked is supposed to do and how you are trying to call it

Hope this helps

5

as Wilson89 explains below, the source of the problem is that the signatures in the header and the cpp do not match. But somehow with tarrays even though I made sure they matched, this error pops up sometimes, because the compiler seems to see it as a const & type in the header, and you only have the simple type (pass by value) in your implementation, so in my case this problem was solved when I used const & both in header and in cpp. (I tried different types - pass by value, reference, const reference, but I think only const reference worked)

Something similar can be found here:

https://answers.unrealengine.com/questions/95396/fail-to-pass-tarray-from-c-to-blueprint.html