Xcode 6 code completion not working

I can't use code completion on Xcode, and I do as the following link then it work:
http://stackoverflow.com/a/27243272

1. Quit Xcode.
2. Restart the computer (this is to clear any in-memory caches).
3. Delete the contents of the DerivedData folder (~/Library/Developer/Xcode/DerivedData), precisely run, a) cd ~/Library/Developer/Xcode/DerivedData/
   b) rm -rf *
4. (Try this if Steps 1-3 dont really work as it rebuilds the cache later on restart which takes time) Delete the contents of folder ~/Library/Caches/com.apple.dt.Xcode, i.e.,
   a) cd ~/Library/Caches/com.apple.dt.Xcode
   b) rm -rf * 

Now launch Xcode

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