"UE4 使用具有自己参数的函数作为参数，C++"

Question

I am trying to set a timer, and use a function with in. I read the timer documentation and figured out how it works. You setting a timer with a timer_handler and a function to execute. Here's the problem. I can only give function without parameters.

GetWorldTimerManager().SetTimer(timer_handle1, this, &actor_class:Foo, 2.f, false, 1.f);

Answer 1

Use the overload of SetTimer<\/code> that takes in a lambda<\/a> . Then call your function with parameters inside the lambda.

GetWorld()->GetTimerManager().SetTimer(
                timer_handle1,
                [&]() { this->Foo(123); },
                2.f,
                false,
                1.f);

Answer 2

You can also do this, Check this out:

Unreal Engine Lambdas for Timers

If you want an action performed just for the duration of a timer or any number of timers, and you don't need to keep that function around, you can also use Unreal Engine's CreateLambda . That way you don't necessarily have to create any extra member methods in your class for a timer specifically.

You can try something like this:

void ADynamicCamera::BlendCameraInAndOut(ACharacter* InCharacter, UCharacterMovementComponent* InCharacterMovement)
{
    if (InCharacterMovement->IsWalking())
    {
        InCharacterMovement->DisableMovement();
        APlayerController* PlayerController = UGameplayStatics::GetPlayerController(this, 0);
        check(PlayerController);
        PlayerController->SetIgnoreLookInput(true);
        PlayerController->SetViewTargetWithBlend(this, BlendTime);
        FTimerHandle TimerHandle;
        /** The first lambda (which happens when the player steps on the TriggerBox) 
         *  can capture the Timerhandle by reference to pass it to the second lambda delegate.
         *  All other values have to be captured by value otherwise you will get a nullptr crash.
         */
        GetWorldTimerManager().SetTimer(TimerHandle, FTimerDelegate::CreateLambda([=, &TimerHandle]
        {
            check(InCharacter);
            PlayerController->SetViewTargetWithBlend(InCharacter, CameraBlendTimer);
            GetWorldTimerManager().SetTimer(TimerHandle, FTimerDelegate::CreateLambda([=]
            {
                check(InCharacterMovement && PlayerController);
                InCharacterMovement->SetMovementMode(MOVE_Walking);
                PlayerController->SetIgnoreLookInput(false);
            }), CameraBlendTimer, false);
        }), CameraBlendTimer, false);
    }
}

Checkout the DelegateSignatureImpl.inl file in the following engine folder, starting from line 139 (UE5) for more information about different function delegates that are available:

"Engine\\Source\\Runtime\\Core\\Public\\Delegates\\DelegateSignatureImpl.inl"

You can also use a custom TFUNCTION wrapper to call on other kinds of delegates, like DYNAMIC_MULTICAST_DELEGATES. That way you can have even more flexibility and additional functionality. You can create your custom wrapper like this:

UCLASS()
class SOME_API ULambdaWrapper final : public UObject
{
    GENERATED_BODY()
public:
    TFunction<void()> CallFunction;

    UFUNCTION()
    void DelegateDispatch() { CallFunctor(); }
};

And call them on your delegates like this:

void AInGameHUD::LoadALevel(const FName& InLevelName)
{
    if (InLevelName != "")
    {
        if (LoadingScreenWidget != nullptr)
        {
            LoadingScreenWidget->SetVisibility(ESlateVisibility::SelfHitTestInvisible);
            LoadingScreenWidget->SetFade(1.0f);
            ULambdaWrapper* LoadingScreenIsDoneFadingWrapper = NewObject<ULambdaWrapper>();
            LoadingScreenIsDoneFadingWrapper->CallFunctor = [this, InLevelName]
            {
                UGameplayStatics::OpenLevel(this, InLevelName);
            };
            LoadingScreenWidget->OnDoneFadingEvent().AddDynamic(LoadingScreenIsDoneFadingWrapper, &ULambdaWrapper::DelegateDispatch);
        }
    }
    else
    {
        UE_LOG(LogUObjectGlobals, Fatal, TEXT("Empty level name. Please add the correct level name and try again."));
    }
}

Objects created from TFUNCTIONs are intended to be used like standard C++ std::function. That is:

• They take a copy of whatever is bound to them, meaning you can return them from functions and store them in objects without caring about the lifetime of the original object being bound. They can also have any number of parameters and have a return type.

TFUNCTION is explained more with an example in Function.h in the following engine folder starting from line 878 (UE5):

"\\Engine\\Source\\Runtime\\Core\\Public\\Templates\\Function.h"

Hope this helps a little.