电脑中装了二个xcode版本，一个是xcode6-beta，一个是xcode5.1.1，每次打开工程时，默认是用xcode6-beta打开。在简介中修改打开方式也没用，没来在*中找到答案
After reading about LaunchServices in OS X I have finally found the solution, thanks for the hint @peter-m.
To modify files association for certain app one can use lsregister tool. So to re-register the app there is-f parameter, and to unregister -u. Everything can be in fact done with just one command:
$ lsregister -f /Applications/Xcode.app
Or if you want to unregister Xcode 5 and not touch manually set associations earlier:
$ lsregister -u /Applications/Xcode5-DP5.app
lsregister is located in /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/, so add it to your $PATH
Re-login to OS X for changes to apply.
简言之，就是在终端输入：
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -u /Applications/Xcode5.app
然后在简介中修改打开方式就OK了。