实现这一目标有多种方法:

通过使用——simulator标志 通过使用——udid标志

首先，您需要列出所有可用的设备。列出所有运行的设备

xcrun simctl list devices

这将给出如下输出:

以下是iOS 13.0之后可用的设备:

== Devices ==
-- iOS 13.6 --
    iPhone 8 (5C7EF61D-6080-4065-9C6C-B213634408F2) (Shutdown) 
    iPhone 8 Plus (5A694E28-EF4D-4CDD-85DD-640764CAA25B) (Shutdown) 
    iPhone 11 (D6820D3A-875F-4CE0-B907-DAA060F60440) (Shutdown) 
    iPhone 11 Pro (B452E7A1-F21C-430E-98F0-B02F0C1065E1) (Shutdown) 
    iPhone 11 Pro Max (94973B5E-D986-44B1-8A80-116D1C54665B) (Shutdown) 
    iPhone SE (2nd generation) (90953319-BF9A-4C6E-8AB1-594394AD26CE) (Booted) 
    iPad Pro (9.7-inch) (9247BC07-00DB-4673-A353-46184F0B244E) (Shutdown) 
    iPad (7th generation) (3D5B855D-9093-453B-81EB-B45B7DBF0ADF) (Shutdown) 
    iPad Pro (11-inch) (2nd generation) (B3AA4C36-BFB9-4ED8-BF5A-E37CA38394F8) (Shutdown) 
    iPad Pro (12.9-inch) (4th generation) (DBC7B524-9C75-4C61-A568-B94DA0A9BCC4) (Shutdown) 
    iPad Air (3rd generation) (03E3FE18-AB46-481E-80A0-D37383ADCC2C) (Shutdown) 
-- tvOS 13.4 --
    Apple TV (41579EEC-0E68-4D36-9F98-5822CD1A4104) (Shutdown) 
    Apple TV 4K (B168EF40-F2A4-4A91-B4B0-1F541201479B) (Shutdown) 
    Apple TV 4K (at 1080p) (D55F9086-A56E-4893-ACAD-579FB63C561E) (Shutdown) 
-- watchOS 6.2 --
    Apple Watch Series 4 - 40mm (D4BA8A57-F9C1-4F55-B3E0-6042BA7C4ED4) (Shutdown) 
    Apple Watch Series 4 - 44mm (65D5593D-29B9-42CD-9417-FFDBAE9AED87) (Shutdown) 
    Apple Watch Series 5 - 40mm (1B73F8CC-9ECB-4018-A212-EED508A68AE3) (Shutdown) 
    Apple Watch Series 5 - 44mm (5922489B-5CF9-42CD-ACB0-B11FAF88562F) (Shutdown) 

然后，您可以从输出中选择名称或uuid，然后按照自己的意愿进行操作。

使用——模拟器运行:

npx react-native run-ios --simulator="iPhone SE"

使用——udid标志运行:

npx react-native run-ios --udid 90953319-BF9A-4C6E-8AB1-594394AD26CE

我希望这个答案对你有帮助。

使用——simulator标志指定一个模拟器。

以下是iOS 14.0之后可用的设备:

npx react-native run-ios --simulator="iPhone 8"
npx react-native run-ios --simulator="iPhone 8 Plus"
npx react-native run-ios --simulator="iPhone 11"
npx react-native run-ios --simulator="iPhone 11 Pro"
npx react-native run-ios --simulator="iPhone 11 Pro Max"
npx react-native run-ios --simulator="iPhone SE (2nd generation)"
npx react-native run-ios --simulator="iPhone 12 mini"
npx react-native run-ios --simulator="iPhone 12"
npx react-native run-ios --simulator="iPhone 12 Pro"
npx react-native run-ios --simulator="iPhone 12 Pro Max"
npx react-native run-ios --simulator="iPhone 13 Pro"
npx react-native run-ios --simulator="iPhone 13 Pro Max"
npx react-native run-ios --simulator="iPhone 13 mini"
npx react-native run-ios --simulator="iPhone 13"
npx react-native run-ios --simulator="iPod touch (7th generation)"
npx react-native run-ios --simulator="iPad Pro (9.7-inch)"
npx react-native run-ios --simulator="iPad (9th generation)"
npx react-native run-ios --simulator="iPad Air (4th generation)"
npx react-native run-ios --simulator="iPad Pro (11-inch) (3rd generation)"
npx react-native run-ios --simulator="iPad Pro (12.9-inch) (5th generation)"
npx react-native run-ios --simulator="iPad mini (6th generation)"

列出所有可用的iOS设备:

xcrun simctl list devices

目前没有办法设置默认值。

React Native Docs:在模拟器上运行

用于iPhone Xʀ模拟器

    "iosxr": "react-native run-ios --simulator=\"iPhone Xʀ\"",

只需将此添加到您的脚本包。json文件

这里使用的字母“ʀ”和“R”是不同的Unicode。

然后点击$ yarn iosxr在iPhone Xʀ模拟器上启动应用程序

这里是改变iOS模拟器的新路径，你只需要改变

default: 'iPhone 6' or something else 

路径:

<project_root>/node_modules/@react-native-community/cli/build/commands/runIOS/runIOS.js

对于RN 0.64.2，配置位于node_modules/@react-native-community/cli-platform-ios/build/commands/runIOS/index.js，您可以修改文件中的默认模拟器

如果你想更改默认设备，只需要运行react-native run-ios，你可以在finder中搜索关键字“runios”，然后打开文件夹和固定index.js文件，将“iphone X”更改为你需要的设备。

[1]: https://i.stack.imgur.com/BCtR1.png