Xcode Playground 一直保持running状态

上stackoverflow上可以找到答案和解决办法
地址：https://stackoverflow.com/questions/39978092/xcode-playground-gets-stuck-on-running-playground-or-launching-simulator-and

reason: 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.

导入UIKit会导致长时间停止在running状态或者卡住。
1、如果不需要UIKit可删除 import UIKit
2、如果需要UIKit，可将平台设置成macOS