Somehow my Xcode settings got messed up as it would only show my Main.storyboard file as XML code. I've been told this can be fixed by selecting the Interface Builder from the "Open As" menu, but there is nothing under the menu (the only "selection" is a greyed-out "<None>"). I've cleared my Xcode caches, but this does not help. Other than that, my project still compiles properly.
How can this be resolved?
As so many people have pointed out, right-click on the file and hover over Open As and select Default - Interface Builder.
However, if this is not an option for you because Open As shows <None>, make sure you are in the standard editor and not the version editor. Go up to View in Xcode menu --> view --> hover over Standard Editor and select Show Standard Editor. Now repeat the steps others have suggested and you should get the results you're looking for.