关闭nodejs终端，重新构建。

关闭js服务器终端，再次运行build

I've never seen this error before, but whenever I can't get Xcode and React-Native to play well together, I do a couple of things. Check what version of Xcode I'm working with. If it needs to be updated, I update it. Then clearing watchman and the cache are the second place I go. I don't use the reset cache command. It always says that I need to verify the cache, so I skip that (you can do it though, I just get confused). I use rm -rf $TMPDIR/react-* to get rid of any cached builds. If that doesn't work, I try to build the app in Xcode, then work my way from there, to build it with react-native run-ios. With this error message, it seems you might start by trying to build it with Xcode. Hope that helps...let me know your progress with it. Good luck! (Also, you could update to RN 0.51 as another attempt to get your versions synced.)

还要确保在模拟器中启用了wifi

对于在iOS上使用CocoaPods遇到同样问题的其他人:

我尝试了上面所有的解决方案，但运气不佳。我在我的项目中有一些本地依赖的包，其中一些需要的pod模块正在安装。问题是React是在我的Podfile中指定的，但是React pod并没有通过使用React -native-git-upgrade自动升级。

修复方法是通过运行cd ios && pod install来升级所有已安装的pod。

我正在使用物理设备，在我的情况下，这解决了问题:

卸载应用程序 Lsof -i:8081 kill -9 PID 重新构建应用程序(react-native run-android或react-native run-ios)