解决的方法：
1.关闭Xcode
2.在终端里执行两行代码：
rm -rf ~/Library/Developer/CoreSimulator/Devices
killall -9 com.apple.CoreSimulator.CoreSimulatorService
实现如下
guominmin:~ mac$ rm -rf ~/Library/Developer/CoreSimulator/Devices
guominmin:~ mac$ killall -9 com.apple.CoreSimulator.CoreSimulatorService
