Xcode playground gets stuck on 'Running playground' or 'Launching simulator' and won't run the code, what to do?

Question

Ans. Switch to macOS platform

When you create a Playground, by default it select iOS platform and automatically imports UIKit. It's the UIKit which crashes and stuck all the time. If your (practice) code does not use UIKit then you can switch to MacOS platform. As major (not exact though) difference between iOS and macOS is in APPKit and UIKit.

In the upper right corner of your Xcode Playground, click on show/hide Utilities--> file inspector --> Playground Setting--> Platform--> macOS

See screenShot below:

I have tried the following and it worked for me:

1. press on the bottom "stop playground" button
2. remove the first comment line and make import statement the first line. no space above import.
3. press execute button

In my case, Xcode 8.3.2, it works when I try as steps below:

1. File -> Close "Name.playground"
2. File -> Close Playground
3. Quit Xcode
4. Re-open Xcode

Buggy Simulator's main process is still working even after Xcode closing. So here're the steps:

1. Quit Xcode;
2. Kill com.apple.CoreSimulator.CoreSimulatorService process in Activity Monitor;
3. Launch Xcode and run your Playground.

In my experience, you should:

1. Prevent Swift playground refresh, by holding: the ► arrow at the bottom left part of the Playground and selecting "Manually Run"
2. Quit Xcode
3. Restart Xcode

It works very well.