How do I migrate a C++ script to a project as a Blueprint?

I am working with both BP and C++. I have someone who made something in C++ and I need to migrate it to a project using BP and read it in BP. How do I do this?

You can make a blueprint that derives from the c++ class. Right click the c++ file in the the content browser and select the “create blueprint that derives…” Can’t remember exact wording. In the c++ class you need the functions you want to call to have the UFUNCTION(BlueprintCallable) specifier and with the variables you can choose many different specifiers like UPROPERTY(BlueprintReadWrite, BlueprintReadOnly) etc.

I get this error after migrating over some BP’s from a C++ project. Do you know what causes this?

It might be to late but avoid changing class structure with editor opened (hot reload) specially if you blueprint base of C++ class, it tends to corrupt blueprints.

The message explains it clear as can be. Your blueprint is already deriving from a c++ class but that class is invalid most likely meaning it doesn’t exist. You need to go into what ever project you are taking the blueprint from → Open the blueprint → click on Class Settings at the top of the blueprint editor and check what class it derives from. Then move that c++ class to your new project before moving the blueprint.

I believe I did what you describe here and it is still happening for me. I am migrating to a new project and here is what i’ve done so far.

  1. Migrate all C++ classes, changed the namespace from OLDPROJECT_API to NEWPROJECT_API

  2. Compile succesfully, open editor.

  3. Migrate Blueprints. At this point all non derived BPs work just fine.

  4. Get this error message, I am unable to select my derived class from the list!

The odd thing is when i create a fresh BP of the proper type it seems to work.