How to programmatically add a component to an actor blueprint within an Editor Plugin?

[mjrmls]

Hello, I’m making a plugin with a few dozen custom classes that are meant to be added to an actor blueprint as components. These are part of a runtime module. I have an editor module in which I’m attempting to create a simple UI.

My goal for this UI is to be able to select one of the plugin’s classes, and click a button : “add class to selected actors in the active level”.

my first thought was to use “Add component by Class”. Here’s my initial attempt to add this functionality to an Editor Utility Widget:

Unfortunately, it seems like this is meant to be called at runtime. It simply doesn’t do anything when I run it and click on the button.

My second attempt was to do it in C++ rather than using blueprints. However I can’t find any way to add a component from a specific class to an already exisiting actor. I’ve found some threads talking about it, but none are applicable here because I want to do this “in-Editor”, i.e. not at runtime.

I also can’t find the source code for the “add component” button inside the Blueprint Editor window, so I don’t know how it’s done there either.

Any help would be immensely appreciated.

[Roy_Wierer.Seda145]

Does AddActorComponent return a component or nullptr?
You should be able to pass in any level actor as WorldContextObject as well, worth testing.
Source code for AddComponent and related methods are in Actor.h and ActorConstruction.cpp.

[Roy_Wierer.Seda145]

@mjrmls

My second attempt was to do it in C++ rather than using blueprints. However I can’t find any way to add a component from a specific class to an already exisiting actor.

Example for a HUD class adding a SceneComponent:

	USceneComponent* WidgetComponentRoot = Cast<USceneComponent>(AddComponentByClass(USceneComponent::StaticClass(), true, FTransform::Identity, false));
	WidgetComponentRoot->AttachToComponent(GetDefaultAttachComponent(), FAttachmentTransformRules(EAttachmentRule::SnapToTarget, EAttachmentRule::SnapToTarget, EAttachmentRule::SnapToTarget, true), NAME_None);

Example how to add an ActorComponent from an ActorComponent to its owning AActor:

UChildActorComponent* CAGrabSlot = Cast<UChildActorComponent>(Owner->AddComponentByClass(UChildActorComponent::StaticClass(), false, FTransform::Identity, false));

[mjrmls]

Infinite thanks for your help, will try these out

[mjrmls]

Does AddActorComponent return a component or nullptr?

It returns the instanced class object, which seems correct. But the target actor doesn’t get anything when I check.

You should be able to pass in any level actor as WorldContextObject as well, worth testing.

Didn’t make a difference sadly

Source code for AddComponent and related methods are in Actor.h and ActorConstruction.cpp.

So I found the definition for AddComponentByClass in ActorConstruction.cpp. However this function isnt used anywhere within Engine\Source\Editor. So I assume the green “Add component” button in the Blueprint editor uses something else. There is something called UK2Node_AddComponentByClass. But it doesn’t seem to be used anywhere relevant either.

I’m still trying things with the bits of code you sent, but my engine keeps crashing when I try it so nothing for now

[UE_FlavienP]

Since 5.0,
you can try to do some of those :
top version you target an instance of a blueprint in the level
bottom version you target a blueprint asset in the content folder.

[mjrmls]

Thanks for this, but I need to do this in ue4. Is it possible to recreate the behaviour of this graph in C++?

[PDubulous]

This works in 5.3

Editor Utility for adding an Actor Component to an Actor posted by PDubulous | blueprintUE | PasteBin For Unreal Engine