问题
I just upgraded to Xcode 4. I have a project that is still dependent on Xcode 3. How can I re-install Xcode 3 and not screw up my current Xcode 4 installation?
回答1:
No problem - the Xcode 3 installer lets you select an installation directory - my preference is to install it in /Developer-old for consistency with the earlier Xcode 4 installers, but you can put it anywhere you like, perhaps even create a subfolder inside the Xcode 4 installation folder for Xcode 3.
回答2:
install it into another directory.
来源：https://stackoverflow.com/questions/5392855/can-i-run-xcode-3-and-xcode-4-at-the-same-time