问题

这个问题发生在旧的RN版本（0.57，0.58（<0.58.4），…）和Xcode 10.3中，其中可用模拟器的名称得到了一些调整 在文件node_modules/@react native community/cli/build/commands/runIOS/findMatchingSimulator.js中，react native尝试通过简单的.startsWith检查选择正确的模拟器。由于重命名，检查现在应该使用.includes（ref）

Found Xcode project appupdateDemo.xcodeproj

Could not find iPhone X simulator

Error: Could not find iPhone X simulator
    at resolve (/Users/topbrids/rn_share_pro/appupdateDemo/node_modules/react-native/local-cli/runIOS/runIOS.js:149:13)
    at new Promise (<anonymous>)
    at runOnSimulator (/Users/topbrids/rn_share_pro/appupdateDemo/node_modules/react-native/local-cli/runIOS/runIOS.js:134:10)
    at Object.runIOS [as func] (/Users/topbrids/rn_share_pro/appupdateDemo/node_modules/react-native/local-cli/runIOS/runIOS.js:106:12)
    at Promise.resolve.then (/Users/topbrids/rn_share_pro/appupdateDemo/node_modules/react-native/local-cli/cliEntry.js:117:22)

解决方案

1. 跟新你的RN版本到0.58.4 +
2. 如果您无法或不会升级到新的RN版本，则可以使用以下命令自动调整findMatchingSimulator.js文件：

sed -i '' 's/startsWith/includes/g' node_modules/react-native/local-cli/runIOS/findMatchingSimulator.js

用这个命令就不用我们去node_modules下面手动修改源码了

还可以把这个命令 放到package.json 的 script节点下面 指定命令 然后用npm run xx 直接执行这个命令 这样用起来更方便一些

{
  "name": "appupdateDemo",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "start": "node node_modules/react-native/local-cli/cli.js start",
    "test": "jest",
    "fixOldRnVersion": "sed -i '' 's/startsWith/includes/g' node_modules/react-native/local-cli/runIOS/findMatchingSimulator.js"
  },
  "dependencies": {
    "react": "16.6.1",
    "react-native": "0.57.7",
    "rn-app-upgrade": "^1.0.4"
  },
  "devDependencies": {
    "babel-jest": "24.9.0",
    "jest": "24.9.0",
    "metro-react-native-babel-preset": "0.57.0",
    "react-test-renderer": "16.6.1"
  },
  "jest": {
    "preset": "react-native"
  }
}

[topbrids@topdeMacBook-Pro appupdateDemo]$ npm run fixOldRnVersion

> appupdateDemo@0.0.1 fixOldRnVersion /Users/topbrids/rn_share_pro/appupdateDemo
> sed -i '' 's/startsWith/includes/g' node_modules/react-native/local-cli/runIOS/findMatchingSimulator.js

react-native run-ios “Could not find iPhone X simulator”