Trying to install iPhone SDK 4, but it won't detect that Xcode has been closed

Question

I've downloaded the iPhone SDK 4 and I started the installer. Everything seemed fine until it entered into the "installation" step, at which point an "Installation Alert" dialog was raised asking me to close Xcode. I closed Xcode right away, but the dialog didn't close. I left to go out for dinner, and found this morning that the dialog was still open. I have tried starting Xcode and closing it again, and clicking on everything I could find. Finally, I tried just closing the installer using Command-Q, but apparently installers cannot be exited that way (an action sheet appeared, explaining that the installer was busy).

So....now what?

Answer 1

If you open up Activity Monitor - is Xcode listed at all?

If it isn't just force quit Installer (Force Quit menu item in the Apple menu) and open it back up.

Answer 2

Restart Mac and try again.

Answer 3

You may have Xcode still running on a different user account.

I had the same problem. (I use Fast User Switching.) When I quit Xcode from that account using Activity Monitor, the installer detected it and continued the installation just fine.