When you use a NoTitleBar theme for the application, it is impossible to use a TabGroup anywhere in the application, because it requires an ActionBar:
1. Create default classic project (which has a TabGroup)
2. In tiapp.xml select a NoTitleBar theme:
3. Run the project and see that the screen is empty (as in screenshot) and logs show:
We should support the theme property we have for Ti.UI.Window so you can select a theme that has a TitleBar when you create a TabGroup in an application that uses a NoTitleBar theme.
On all other windows, use the theme property to select a NoTitleBar theme.