AActor::PreEditChange(FEditPropertyChain&) is missing

Development Platform & Builds
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1

If you subclass AActor and override the FEditPropertyChain& variant of PreEditChange(), a call to Super::PreEditChange(PropertyAboutToChange) will fail to compile because of C++'s [annoy and ancient] overload hiding rules.

Fix is that AActor should have a “using Super::PreEditChange;” line above the existing method declaration to bring forward both argument signatures.

More info about overload hiding: https://stackoverflow.com/questions/6727087/c\-virtual\-function\-being\-hidden

   Example of errors:
3>C:\myProj\myProj\Source\myProj\MyActor.cpp(715): error C2664: 'void AActor::PreEditChange(FProperty *)': cannot convert argument 1 from 'FEditPropertyChain' to 'FProperty *'
3>C:\myProj\myProj\Source\myProj\MyActor.cpp(715): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
3>C:\myProj\Unreal\Engine\Source\Runtime\Engine\Classes\GameFramework\Actor.h(2324): note: see declaration of 'AActor::PreEditChange'
3>C:\myProj\myProj\Source\myProj\MyActor.cpp(715): note: while trying to match the argument list '(FEditPropertyChain)'
2

Steps to Reproduce

UCLASS()
class AMyActor : public AActor
{
    GENERATED_BODY()

public:
#if WITH_EDITOR
    virtual void PreEditChange(FEditPropertyChain& PropertyAboutToChange) override
    {
        // Placeholder
        static int x =0;
        ++x;

        Super::PreEditChange(PropertyAboutToChange); // <-- Error here
    }
#endif
};
3

Hello Phillip,

You are correct in noticing that there is no chain version of PreEditChange and probably should be, but I don’t think your suggested fix is a good idea. Support for PreEditChange(FEditPropertyChain) is currently not supported well in the engine, and there are many places that just call it directly with PreEditChange(FProperty*) so your override is unlikely to be called in most situations. UObject::PreEditChange(FEditPropertyChain) calls the single property version to work around this. If you do have a specific need to override the chain version, you should be able to avoid the compile error by calling UObject::PreEditChange(PropertyAboutToChange) directly, like how UVCamComponent does.

I definitely agree that the current state of this in the engine is not great so we will put in a JIRA to track the general problem.

4

Okay. We’ll just keep this change local then.