XCode 4 Adding a Sub Project
Sorry to revamp the old question, but I just got the absolute answer for this problem.... maybe this can help the other....
To add Sub-Project to current project, It just simply drag the .xcodeproj from finder to xcode, place it in your project...
BUT... there is something must be done before doing this.... JUST OPEN ONE XCODE INSTANCE.... So, close the other instance when dragging .xcodeproj to xcode....
If you drag it while opening few xcode instance (opening few project at once), the .xcodeproj that you dragged can't be expanded and not just what you want...
hope this can help the other....
Regards