I have the weirdest issue with Xcode 6 on OS X Yosemite. For some reason I can't use the left and right arrow keys anymore to navigate within my source code. Instead, the system beep sound would come up. Up and down arrows work fine.
I'm afraid it could have something to do with my fiddling around with the key bindings. In only changed the ones for block (de)indentation though (originally CMD+[, changed to TAB), so in my understanding the arrow keys shouldn't be affected at all.
I was able to make it work again by running
defaults delete com.apple.dt.Xcode
in the terminal and then restarting Xcode.
来源：https://stackoverflow.com/questions/24631146/arrow-keys-in-xcode-6-not-working