Recently I’ve been enjoying learning more about Common UI, the new-ish Unreal UI system that’s used in Fortnite. The new widgets, input system, and navigation make it easy to quickly put together menu flows. However, every now and then in my C++ based projects Blueprint classes keep losing their parent class. The end result is that when I open my uproject all the CommonUI.CommmonActivatableWidget’s are corrupted. The Blueprint’s themselves no longer able to be opened. Entire UI, broken. 😭

I was nearing a breaking point this weekend, contemplating going back to UMG when I stumbled across this forum post. In the Blueprint Keeps Losing Parent post, which was unrelated to Common UI, the group comes to the conclusion that the bug is a side effect of the Live Coding feature introduced in UE 4.22. In other side projects I have Live Coding disabled as it’s caused a number of frustrating issues when opening the editor. For instance working on my intersection testing demo, actors like NearestPointToLineActor would fail to load and would result in a broken Level file. Since then I’ve been disabling it, but forgot to do so in my Common UI playgrounds. Disabling Live Coding as “fixed” my issue. I just need to make sure run through Visual Studio rather than launching through the Epic Launcher. If you really need Live Coding enabled and you run into this, here’s a “quick” way to fix things up.

  1. Hope you’re using source control or have a backup
  2. Close the editor
  3. Delete corrupted blueprints
  4. Rebuild from Visual Studio
  5. Open the editor or launch from VS
  6. Force sync / replace corrupted blueprints from backup while the editor is open

The only annoyance I’ve run into with this workaround is that I had to manually fix up any Blueprints that had a Create Widget node as the out value from them was broken.