Two Xcode app icons in launchpad after 4.5 install

If moving the app to trash and back does not solve the problem, try this command in the Terminal before you move the app back from the trash:

killall Dock

The easiest way to fix this is to head to your applications folder, (Using the menu bar, not a dock folder) and manually moving Xcode to your trash. After that, open launchpad and let it update. Both Xcodes will be gone. Then open your trash and right click Xcode, select Put Back. Voila, you fixed your problem and didn't even have to re-download!

Run command in terminal will reset launchpad, it works for me

defaults write com.apple.dock ResetLaunchPad -bool true; killall Dock

NOTE: This will reset arrangement of you apps order by alphabetic.