最近原来的老项目有点问题需要处理一下，运行启动命令，就报了如下错误，提示找不到iPhone 6 模拟器。

react-native run-ios

Owaiss-Mac:pdm owaisahmed$ react-native run-ios
Found Xcode project pdm.xcodeproj

Could not find iPhone 6 simulator

Error: Could not find iPhone 6 simulator
    at resolve (/Users/fantuan/Documents/react-native-projects/pdm/node_modules/react-native/local-cli/runIOS/runIOS.js:149:13)
    at new Promise (<anonymous>)
    at runOnSimulator (/Users/fantuan/Documents/react-native-projects/pdm/node_modules/react-native/local-cli/runIOS/runIOS.js:134:10)
    at Object.runIOS [as func] (/Users/fantuan/Documents/react-native-projects/pdm/node_modules/react-native/local-cli/runIOS/runIOS.js:106:12)
    at Promise.resolve.then (/Users/fantuan/Documents/react-native-projects/pdm/node_modules/react-native/local-cli/cliEntry.js:117:22)

老项目是一年前的当时项目的的版本时还是0.57，期间工作电脑的系统版本升级到了10.14.6， XCode的版本也升级到了10.3，使用如下命令可以查看当前项目的具体环境信息：

React Native Environment Info:
    System:
      OS: macOS 10.14.6
      CPU: (8) x64 Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz
      Memory: 26.40 MB / 16.00 GB
      Shell: 5.3 - /bin/zsh
    Binaries:
      Node: 10.14.1 - ~/.nvm/versions/node/v10.14.1/bin/node
      Yarn: 1.13.0 - ~/.nvm/versions/node/v10.14.1/bin/yarn
      npm: 6.4.1 - ~/.nvm/versions/node/v10.14.1/bin/npm
      Watchman: 4.9.0 - /usr/local/bin/watchman
    SDKs:
      iOS SDK:
        Platforms: iOS 12.4, macOS 10.14, tvOS 12.4, watchOS 5.3
      Android SDK:
        API Levels: 23, 25, 26, 27, 28, 29
        Build Tools: 23.0.1, 23.0.3, 25.0.2, 25.0.3, 26.0.3, 27.0.3, 28.0.0, 28.0.2, 28.0.3, 29.0.2
        System Images: android-23 | Intel x86 Atom, android-23 | Intel x86 Atom_64, android-23 | Google APIs Intel x86 Atom_64, android-29 | Google APIs Intel x86 Atom
    IDEs:
      Android Studio: 3.1 AI-173.4720617
      Xcode: 10.3/10G8 - /usr/bin/xcodebuild
    npmPackages:
      react: 16.5.0 => 16.5.0
      react-native: 0.57.0 => 0.57.0
    npmGlobalPackages:
      react-native-cli: 2.0.1
      react-native-create-library: 3.1.2

经过一番查阅资料发现是Xcode的版本升级到10导致的。 解决方案如下： 1.打开项目node_modules/react-native/local-cli/runIOS/findMatchingSimulator.js文件 2.修改文件的第31行

if (!version.startsWith('iOS') && !version.startsWith('tvOS')) {
  continue;
}

为如下代码

if (!version.startsWith('com.apple.CoreSimulator.SimRuntime.iOS') 
    && !version.startsWith('com.apple.CoreSimulator.SimRuntime.tvOS')) {
  continue;
}

吐血注意： 对于ReactNative项目开发中，请不要轻易升级Xcode等编译，除非你十分精通。

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