Opening my project with Xcode 9 beta, all storyboards and xib files open as xml when selected. When I double-click them, they launch with IB as standalone windows. Is this the new standard behavior? Is there a new setting?
I stumbled on the solution. They are working now. When I initially opened the storyboard, the xml appeared in both the main and assistant editors. When I loaded a corresponding view controller source in the assistant editor, the main editor switched to the IB view. From then on, all storyboards and xibs loaded as IB views. Not sure if it's a bug or a feature.