Getting child component from actor

Development Programming & Scripting C++
1

I’m trying to teleport to a location when using a door using the following code:


FHitResult* HitResult = new FHitResult();
	FVector StartTrace = FirstPersonCameraComponent->GetComponentLocation();
	FVector ForwardVector = FirstPersonCameraComponent->GetForwardVector();
	FVector EndTrace = ((ForwardVector*250.0f) + StartTrace);
	FCollisionQueryParams* TraceParams = new FCollisionQueryParams();

	if (GetWorld()->LineTraceSingleByChannel(*HitResult,StartTrace,EndTrace,ECC_Visibility,*TraceParams))
	{
		DrawDebugLine(GetWorld(), StartTrace, EndTrace, FColor(255, 0, 0),true);
		GEngine->AddOnScreenDebugMessage(-1, 5.0f, FColor::Red, FString::Printf(TEXT("You hit: %s"),*HitResult->Actor->GetName()));
		if (HitResult->Actor->GetName() == "Door1")
		{
			SetActorLocation() //I want to put the location of a child compononent of my HitResult->Actor
			
		}

This is the Hitresult->Actor , I want to get the location of the destination component, how do I get it through code
6dd502d81b91755ce76a8cd3dd50969b.png

2 


ADoorTrigger *HitDoorTrigger = Cast<ADoorTrigger>(HitResult->Actor);
if (HitDoorTrigger){
    HitDoorTrigger->Destination->GetComponentLocation();
    //etc...
}

The Cast<>() will convert the hit result pointer into your custom door trigger class if you hit a door trigger, letting you access its members like the Destination component. If it’s not a door trigger the Cast will return nullptr, so that allows you to check it and only do certain code if the hit actor is a certain type. Cast<>() is very important for a lot of things in UE4, so it’s worth learning how to use it.

3

It says ADoorTrigger is undifined. And I can’t make that class public for some reason?

6b05a08bbccd64257b3e908e22a600d3.png

4

Ok so, it’s not a matter of public/private (C++ doesn’t have public/private classes), it’s the fact that ADoorTrigger isn’t defined in the .cpp you’re trying to use it in, what you need to do is #include “DoorTrigger.h” in the .cpp file that is using the Cast<>() so that it knows what an ADoorTrigger class is. Each .cpp file is compiled separately and only knows about the classes that you #include (and basic classes that MSVC and UE4 always include). This is a basic C++ thing, so you should probably go through some tutorials to get a better understanding, otherwise you’ll run into a lot more problems down the road.

5

Yea, I’ve always used c# so alot is new for me.

Now it works by the way!
I used:
ADoorTrigger *HitDoorTrigger = Cast<ADoorTrigger>(HitResult);

Thanks alot for your help!

6

Ok nevermind, my code didn’t compile.

I’ve tried what you said and got a syntax error:


	if (GetWorld()->LineTraceSingleByChannel(*HitResult,StartTrace,EndTrace,ECC_Visibility,*TraceParams))
	{
		DrawDebugLine(GetWorld(), StartTrace, EndTrace, FColor(255, 0, 0),true);
		GEngine->AddOnScreenDebugMessage(-1, 5.0f, FColor::Red, FString::Printf(TEXT("You hit: %s"),*HitResult->Actor->GetName()));
		if (HitResult->Actor->GetName() == "Door1")
		{
			ADoorTrigger *HitDoorTrigger = Cast<ADoorTrigger>(HitResult->Actor);
			if (HitDoorTrigger) {
				SetActorLocation(HitDoorTrigger->Destination->GetComponentLocation());
			}
			
		}
	}

error: no instance of overloaded function “Cast” matches the argument list

7

Oh, I forgot that HitResult->Actor is actually a TWeakObjectPtr<AActor>, not a raw pointer, so the argument type is wrong and the compiler is telling you about it. You should use Cast<ADoorTrigger>(HitResult->Actor->Get()). UE4 sometimes uses wrappers around raw pointers, like TSharedPtr or TWeakObjectPtr for safer handling. These pointer wrappers have accessor methods like Get(), or * to give you the raw pointer. You could have used the code suggestions to look at the types of FHitResult::Actor and the arguments that Cast expects and figured this out for yourself though.

8

Just want to add to make sure you’re including “DoorTrigger.h” at the top of your class, so the class knows what an ADoorTrigger is.

9

Thanks for the replies. HitResult->GetActor() worked too :slight_smile: