Flutter终于推出2.0版本了，兴奋升级尝鲜后发现编译的时候webview_flutter报错：undefined method `each_child' for #<Dir:0x007fb3fb295160>。
关键日志信息如下：

Running pod install...
CocoaPods' output:
↳
      Preparing

    Analyzing dependencies

    Inspecting targets to integrate
      Using `ARCHS` setting to build architectures of target `Pods-Runner`: (``)

    ......

    Comparing resolved specification to the sandbox manifest
      - Flutter
      - webview_flutter

    Downloading dependencies

    -> Using Flutter (1.0.0)

    ......
      - Generating deterministic UUIDs
      - Stabilizing target UUIDs
      - Running post install hooks
    [!] An error occurred while processing the post-install hook of the Podfile.

    undefined method `each_child' for #<Dir:0x007fb3fb295160>
    Did you mean?  each_slice

    /Users/shuaitao/Library/flutter/packages/flutter_tools/bin/podhelper.rb:54:in `block in flutter_additional_ios_build_settings'
    /Users/shuaitao/Library/flutter/packages/flutter_tools/bin/podhelper.rb:51:in `each'
    /Users/shuaitao/Library/flutter/packages/flutter_tools/bin/podhelper.rb:51:in `flutter_additional_ios_build_settings'
    /Users/shuaitao/Project/moxie/ios/Podfile:39:in `block (3 levels) in from_ruby'
    /Users/shuaitao/Project/moxie/ios/Podfile:38:in `each'
    /Users/shuaitao/Project/moxie/ios/Podfile:38:in `block (2 levels) in from_ruby'
    /Users/shuaitao/.rvm/gems/ruby-2.4.1/gems/cocoapods-core-1.10.1/lib/cocoapods-core/podfile.rb:179:in `post_install!'
   ......

Error output from CocoaPods:
↳

    [!] Automatically assigning platform `iOS` with version `9.0` on target `Runner` because no platform was specified. Please specify a platform for this target in your Podfile. See `https://guides.cocoapods.org/syntax/podfile.html#platform`.

Error running pod install
Error launching application on iPhone 12 Pro Max.

经过调查发现，Dir.each_child方法是ruby 2.5版本才支持，使用ruby -v看到本地安装的是ruby 2.4.1版本。知道问题原因后，接下来的解决方案是使用rvm install 2.5.1升级ruby的版本：

rvm install 2.5.1

如果升级的过程中有可能会遇到No fallback URL could be found错误， 详细错误日志如下：

Checking fallback: https://ftp.ruby-lang.org/pub/ruby/2.5/ruby-2.5.1.tar.bz2
No fallback URL could be found, try increasing timeout with:

    echo "export rvm_max_time_flag=20" >> ~/.rvmrc

There has been an error fetching the ruby interpreter. Halting the installation.

根据具体执行echo "export rvm_max_time_flag=20" >> ~/.rvmrc指令，并再次执行ruby升级命令即可：

echo "export rvm_max_time_flag=20" >> ~/.rvmrc
rvm install 2.5.1

最后，ruby升级完成后需要彻底删除 webview_flutter组件，重启IDE后，再次集成 webview_flutter组件即可。