I recently installed Xcode 9.0 GM on my machine. I fired it up to play around and the only simulators I see in the scheme are iPhone 8, iPHone 8 Plus, and iPhone X. I clicked "Download Additional Simulators" thinking the solution would lie there.
I'm greeted with this screen, which is everything I previously had installed.
I dug around on the Apple Developer forum and found this post discussing a similar problem with a prior version of iOS. At the suggestion of one of the posters, I powered down my machine and booted it cold. I opened up Xcode 9.0 again and I have the same issue.
Any suggestions what I can get additional hardware to appear in my Xcode scheme? Thank you for reading.
Delete every single one of the simulators listed in the Devices and Simulators window, one by one, and then start over make new simulators. That always works for me. It's a good idea after any upgrade, in fact.
In Xcode 10.3, I also lost all simulators but got them back by running
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
In case anyone else gets here and are in my situation, I just upgraded to XCode 9.2 and the simulators were all missing, but quitting and relaunching XCode restored them.
For me quitting and relaunching XCode also didn't help. So I did the following 3 steps.
Three steps
Step 1:
Product -> Destination -> Download Simulators... Download the simulator(s) you need
Step 2:
Sometimes when you download the new simulator types, they don't automatically show in the list of possible simulators.
Product -> Destination -> Add Additional Simulators... Click the + button in the lower left hand corner, then Add Simulator Give it a name, device type, and the iOS version you just downloaded.
Step 3:
Set proper deployment target. If you have downloaded simulators of lower versions,set the deployment target to the same.
Now it should show up in your list of simulator devices!
来源：https://stackoverflow.com/questions/46259983/xcode-9-0-simulators-disappeared