I have a component that can attach its self to other components based on the proximity to another static mesh. It does this after the actor (that it’s a part of) is moved. This seems to work fine. If you duplicate the attached actor, it will become detached if it and the actor/component it’s attached to are not in the persistent level.
Using the project I provided, you can reproduce this by…
Open TestMap.uproject
Make sure that TestMap_B is the active map.
Grab the blue cube (BP_AutoAttachActor) and move it close to the cube underneath it (BP_SpinningActor).
Once you see it’s attached, PIE. The blue cube appears attached to the spinning cube.
Stop the PIE instance and duplicate the blue cube. Alt-Drag and Ctrl+D seem to produce the same results.
Place the new cube onto one of the spinning cubes.
Start a PIE instance.
The original cube is detached, but the new cube is attached.
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I’m running into an issue where an actor is becoming detached when it’s duplicated and in a sub-level.
To start off, I have a component that can attach its self to other components based on the proximity to another static mesh. It does this after the actor (that it’s a part of) is moved. This seems to work fine. If you duplicate the attached actor, it will become detached if it and the actor/component it’s attached to are not in the persistent level.
I had a look at the project and I think the problem is that BP_AutoAttachActor is part of the TestMap while it’s being attached to BP_SpinningActor that is part of TestMap_B. This is resulting in a bug where the BP_SpinningActor instance from the Editor world is being dragged in PIE.
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If I duplicate BP_AutoAttachActor, the new instances is part of TestMap_B and properly attaches to the right instance, ie the PIE one.
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I’ll have a colleague validate the information but I’m pretty sure that Actors can be attached to instances that are not in the same level.
Sorry, I meant to move that into TestMap_B. If you move it to TestMap_B, save the maps, move it so that it attaches, and hit play. It’ll look attached correctly. If you re-open the map, it’ll be snapped to the center of that box it was attached to.
I ran some extra tests and I’m not sure that you can preserve that type of attachment through a save\load cycle. You might get more success if you attach to a socket in the Parent StaticMesh but I doubt you want to add sockets to everything. I traced the problem back to the calculation of the transform at load time. It appears that some of the hierarchy is not properly initialized but I couldn’t find a way to force an update.
You might have to store the desired transform in the UAutoAttachComponent and restore it after the initialization.
I should not that attaching to the GetDefaultAttachComponent (the rootcomponent of the Hit Actor) does properly restore the transform. I suspect that the Parent Actor has not been properly initialized at the attachment time and its child ComponentToWorld is not valid at that point.
I reached out to a few colleagues that are more familiar with that part of the engine. I’ll report back if they have some suggestions.