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Compiling an actor blueprint crashes to desktop

Hello! I've been doing some work using modular components on actors and have found that under very specific circumstances compilation can trigger a crash to desktop. The consistent steps to reproduce the crash are:

  1. Attempt to delete a component from the content browser.

  2. Cancel the deletion.

  3. Open an actor that has the same component attached.

  4. Detach (delete) the component from the actor.

  5. Attempt compile the actor blueprint Crash happens before the compile finishes

The actor in question does not (currently) compile its blueprint due to errors. The crash does not happen if step 1) and 2) are not performed, in that case, attempting to detach the component and compile work just fine (compilation fails and displays all existing errors).

Hope that helps anyone.

Product Version: UE 4.9
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asked Oct 03 '15 at 01:42 AM in Bug Reports

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avatar image GoodOldMalk Oct 03 '15 at 06:39 AM

I have pinpointed the problem to an unimplemented function for the specific actor I'm using. When a function is not properly wired, attempting to compile the blueprint results in a crash to desktop under multiple conditions, not just the one listed above.

The above can't be replicated in copies, instances or new actors. The actor I'm using pre-dates version 4.9.

avatar image Ben Halliday STAFF Oct 03 '15 at 05:40 PM

Hi GoodOldMalk,

Please copy the information in the Crash Reporter window and paste it here, including the Machine ID. Make sure to hit Send. Then, attach the log from the project's \Saved\Logs folder.

I'm not able to reproduce this in a new project with new actors, as you mentioned, nor with an Actor from a project upgraded from 4.8. I'll see if I can link the information from your log and Crash Report to any known issues, otherwise there probably isn't much we can do if we can't reproduce it.

If you're able to reproduce it in a new project at any point, please let us know and upload the project someplace we can get at it to look it over. Thanks!

avatar image GoodOldMalk Oct 03 '15 at 06:06 PM

I'm unable to paste the entirety of the crash report here so I've attached a text file instead.



"Assertion failed: ((UObject*)ContainerPtr)->IsA((UClass*)GetOuter()) [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.9\Engine\Source\Runtime\CoreUObject\Public\UObject\UnrealType.h]



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Hey GoodOldMalk,

This looks very similar to another bug report we have (UE-21255), and I see another few projects have reported the same crash in 4.9. I've created UE-21759 to track the issue, and I'll let you know when I see any update on it. Thanks for the report!

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answered Oct 03 '15 at 07:53 PM

avatar image Ben Halliday STAFF Oct 06 '15 at 12:38 PM

Hey GoodOldMalk,

The developers have requested a repro project. If possible, please zip the project in which this occurs and upload it someplace like Google Drive or Dropbox, and send me a download link via PM on the forums:


Please include the steps we'd need to reproduce this issue in the project you send. Thanks!

avatar image GoodOldMalk Oct 06 '15 at 05:37 PM

Regretably for debugging, I've done a number of changes that seemed to have removed the crash.

I've started moving away the controller logic from the Actor to the PlayerController, including components and component interfaces, and in the process the bug can not be replicated anymore. I've also revised my interfaces so that they pass structures (at worst, with default values) instead of arrays (which could possibly be empty), so getting a compilation error from unwired interfaces is no longer possible.

avatar image Ben Halliday STAFF Oct 06 '15 at 05:40 PM

Okay, no problem. If you manage to reproduce it again, please send me the project. Thanks!

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