Classes folder not appearing in Groups & Files Xcode

The code files have suddenly disappeared from the 开发者_如何学编程left tree pane on my Xcode. I tried to drag and drop the classes folder from the file system but this starts giving syntax errors. Please help.

If the project builds then you haven't deleted them, you've probably dragged them into another group[ by mistake :)

Open all the other groups and you might see the Classes folder as a subfolder. Just drag it back out again.

NB Go to Build->'Clean all Targets' and then build it again. If it builds without errors then my answer is probably right. If it doesn't build then I'm absolutely wrong :)