podhelper.rb源码解析

前言：iOS工程中引入flutter。我们第一步要做的事是，在podfile里面写入类似下面代码。

flutter_app_path = '../my_flutter' #flutter工程目录
load File.join(flutter_app_path, '.ios', 'Flutter', 'podhelper.rb') #导入podhelper.rb文件
install_all_flutter_pods(flutter_app_path) #调用podhelper.rb文件的install_all_flutter_pods方法

下面分析podhelper.rb都干了啥。
总体结构：1个require、6个方法

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Part1、require语法

require 'json'

require。类似于include和import，引入一个模块。模块（Module）是一种把方法、类和常量组合在一起的方式。提供了命名空间、实现了混入(mixin)
Load和require都能加载。模块的状态会频繁地变化, 我们使用 load 进行加载，获取最新的状态。不变化的我们用require。

Part2、6个方法

1、install_all_flutter_pods

def install_all_flutter_pods(flutter_application_path = nil)
  flutter_application_path ||= File.join('..', '..')
  install_flutter_engine_pod
  install_flutter_plugin_pods(flutter_application_path)
  install_flutter_application_pod(flutter_application_path)
end

1、def：定义一个方法
2、||=：或等，为空则赋值，不为空自身
3、File.join('..', '..')：用分割符(默认是/)把'..'和'..'组合起来，返回一个str。该例子返回一个'../..'

2、install_flutter_engine_pod

def install_flutter_engine_pod
  current_directory = File.expand_path('..', __FILE__)
  engine_dir = File.expand_path('engine', current_directory)
  if !File.exist?(engine_dir)
    # Copy the debug engine to have something to link against if the xcode backend script has not run yet.
    # CocoaPods will not embed the framework on pod install (before any build phases can generate) if the dylib does not exist.
    debug_framework_dir = File.join(flutter_root, 'bin', 'cache', 'artifacts', 'engine', 'ios')
    FileUtils.mkdir_p(engine_dir)
    FileUtils.cp_r(File.join(debug_framework_dir, 'Flutter.framework'), engine_dir)
    FileUtils.cp(File.join(debug_framework_dir, 'Flutter.podspec'), engine_dir)
  end

  # Keep pod path relative so it can be checked into Podfile.lock.
  # Process will be run from project directory.
  engine_pathname = Pathname.new engine_dir
  # defined_in_file is set by CocoaPods and is a Pathname to the Podfile.
  project_directory_pathname = defined_in_file.dirname
  relative = engine_pathname.relative_path_from project_directory_pathname

  pod 'Flutter', :path => relative.to_s, :inhibit_warnings => true
end

1、__FILE__。这个变量代表文件自己的文件名，在podhelper.rb中是podhelper.rb。
2、File.expand_path('..', 'b')。在b路径下追加路径'..'，此例是b/..，也就是返回b的上级目录。
3、flutter_root。方法
4、FileUtils.mkdir_p。生成目录及其所有上级目录。例如，FileUtils.mkdir_p '/usr/local/lib/ruby'将生成下列所有目录(若没有的话)。 * /usr * /usr/local * /usr/local/bin * /usr/local/bin/ruby
5、FileUtils.cp_r(a,b)。把文件a拷贝到b，如果目录b存在，就拷贝到b里面，如果b不存在，就把a拷贝到b，此时b是一个没有后缀名的文件
6、Pathname.new engine_dir。等同Pathname.new(engine_dir)，或Pathname(engine_dir)。通过str生成一个路径类Pathname的对象
7、a.relative_path_from b。a相对于b的相对路径，也叫b->a的相对路径。Pathname('/Users/bigfly/Desktop').relative_path_from Pathname('/Users/bigfly/Desktop/my_flutter')是'..'
8、.to_s。用来将对象以字符串的格式去描述、去输出。也就是说，所有对象都能使用字符串的描述格式。
只要像鸭子，就能当成鸭子，这就是to_x。只有它真的是鸭子，才能当成鸭子，这就是to_xxx。例如调用obj的string方法时需要先强制转换为string类，用to_str。类似的有to_i和to_int、to_a和to_ary、to_h和to_hash

总结：该方法是把flutter_root目录/Users/xxx/flutter/bin/cache/artifacts/engine/ios 下面的Flutter.framework和Flutter.podspec拷贝到flutter模块工程的engine目录/Users/bigfly/Desktop/my_flutter/.ios/Flutter/engine下面。然后把Flutter pod进来。如果engine存在就直接pod，如果不存在，就去flutter_root拷贝一份过来再pod。

3、install_flutter_plugin_pods

def install_flutter_plugin_pods(flutter_application_path)
  flutter_application_path ||= File.join('..', '..')

  # Keep pod path relative so it can be checked into Podfile.lock.
  # Process will be run from project directory.
  current_directory_pathname = Pathname.new File.expand_path('..', __FILE__)
  # defined_in_file is set by CocoaPods and is a Pathname to the Podfile.
  project_directory_pathname = defined_in_file.dirname
  relative = current_directory_pathname.relative_path_from project_directory_pathname
  pod 'FlutterPluginRegistrant', :path => File.join(relative, 'FlutterPluginRegistrant'), :inhibit_warnings => true

  symlinks_dir = File.join(relative, '.symlinks')
  FileUtils.mkdir_p(symlinks_dir)

  plugins_file = File.expand_path('.flutter-plugins-dependencies', flutter_application_path)
  plugin_pods = flutter_parse_dependencies_file_for_ios_plugin(plugins_file)
  plugin_pods.each do |plugin_hash|
    plugin_name = plugin_hash['name']
    plugin_path = plugin_hash['path']
    if (plugin_name && plugin_path)
      symlink = File.join(symlinks_dir, plugin_name)
      FileUtils.rm_f(symlink)
      File.symlink(plugin_path, symlink)
      pod plugin_name, :path => File.join(symlink, 'ios'), :inhibit_warnings => true
    end
  end
end

1、flutter_application_path：/Users/xxx/Desktop/my_flutter
2、current_directory_pathname：/Users/xxx/Desktop/my_flutter/.ios/Flutter
3、project_directory_pathname = /Users/xxx/Desktop/my_flutter/.ios
4、symlinks_dir = /Users/xxx/Desktop/my_flutter/.ios/Flutter/.symlinks
5、plugins_file = /Users/xxx/Desktop/my_flutter/.flutter-plugins-dependencies
6、flutter_parse_dependencies_file_for_ios_plugin。方法。解析.flutter-plugins-dependencies这个json文件，返回一个key链plugins/ios的值
7、FileUtils.rm_f(symlink)：删除/Users/xxx/Desktop/my_flutter/.ios/Flutter/.symlinks/shared_preferences
File.symlink(plugin_path, symlink)：在symlink位置创建一个符号链接，指向plugin_path，此处plugin_path的值是"/Users/xxx/flutter/.pub-cache/hosted/pub.flutter-io.cn/shared_preferences-0.5.12/"

总结：该方法是，先pod进来/Users/xxx/Desktop/my_flutter/.ios/Flutter/FlutterPluginRegistrant。然后解析.flutter-plugins-dependencies文件，得到key链plugins/ios的值，是个依赖库数组，遍历数组，对每个依赖库进行删除实体文件、创建符号链接、pod进来操作。

4、install_flutter_application_pod

def install_flutter_application_pod(flutter_application_path)
  current_directory_pathname = Pathname.new File.expand_path('..', __FILE__)
  app_framework_dir = File.expand_path('App.framework', current_directory_pathname.to_path)
  app_framework_dylib = File.join(app_framework_dir, 'App')
  if !File.exist?(app_framework_dylib)
    # Fake an App.framework to have something to link against if the xcode backend script has not run yet.
    # CocoaPods will not embed the framework on pod install (before any build phases can run) if the dylib does not exist.
    # Create a dummy dylib.
    FileUtils.mkdir_p(app_framework_dir)
    `echo "static const int Moo = 88;" | xcrun clang -x c -dynamiclib -o "#{app_framework_dylib}" -`
  end

  # Keep pod and script phase paths relative so they can be checked into source control.
  # Process will be run from project directory.

  # defined_in_file is set by CocoaPods and is a Pathname to the Podfile.
  project_directory_pathname = defined_in_file.dirname
  relative = current_directory_pathname.relative_path_from project_directory_pathname
  pod 'my_flutter', :path => relative.to_s, :inhibit_warnings => true

  flutter_export_environment_path = File.join('${SRCROOT}', relative, 'flutter_export_environment.sh');
  script_phase :name => 'Run Flutter Build my_flutter Script',
    :script => "set -e\nset -u\nsource \"#{flutter_export_environment_path}\"\n\"$FLUTTER_ROOT\"/packages/flutter_tools/bin/xcode_backend.sh build",
    :input_files => [
      File.join('${SRCROOT}', flutter_application_path, '.metadata'),
      File.join('${SRCROOT}', relative, 'App.framework', 'App'),
      File.join('${SRCROOT}', relative, 'engine', 'Flutter.framework', 'Flutter'),
      flutter_export_environment_path
    ],
    :execution_position => :before_compile
end

1、current_directory_pathname = /Users/xxx/Desktop/my_flutter/.ios/Flutter
2、app_framework_dir = /Users/xxx/Desktop/my_flutter/.ios/Flutter/App.framework
3、app_framework_dylib = /Users/xxx/Desktop/my_flutter/.ios/Flutter/App.framework/App
4、echo "static const int Moo = 88;" | xcrun clang -x c -dynamiclib -o "#{app_framework_dylib}" -。shell命令
5、${SRCROOT}，ruby中全局变量用${}引用
6、project_directory_pathname = /Users/xxx/Desktop/my_flutter/.ios
7、flutter_export_environment_path =/Users/xxx/Desktop/my_flutter/.ios/Flutter/flutter_export_environment.sh
8、script_phase 。给target添加编译前的shell脚本，脚本内容是

set -e #之后的代码，一旦出错，停止执行并退出，避免后续一些脚本的危险操作
set -u #遇到不存在的变量就会报错，并停止执行
source "#{flutter_export_environment_path}"
"$FLUTTER_ROOT"/packages/flutter_tools/bin/xcode_backend.sh build

总结：该方法是，生成App.framework/app文件如果不存在的话，执行了一条shell命令(调用xcrun clang -o命令生成目标文件)。pod进来my_flutter。给target添加编译前的shell脚本，脚本主要执行了xcode_backend.sh build命令。

5、flutter_parse_dependencies_file_for_ios_plugin

def flutter_parse_dependencies_file_for_ios_plugin(file)
  file_path = File.expand_path(file)
  return [] unless File.exists? file_path

  dependencies_file = File.read(file)
  dependencies_hash = JSON.parse(dependencies_file)

  # dependencies_hash.dig('plugins', 'ios') not available until Ruby 2.3
  return [] unless dependencies_hash.has_key?('plugins')
  return [] unless dependencies_hash['plugins'].has_key?('ios')
  dependencies_hash['plugins']['ios'] || []
end

解析.flutter-plugins-dependencies文件，并返回key链plugins/ios的值。

6、flutter_root

def flutter_root
  generated_xcode_build_settings_path = File.expand_path(File.join('..', '..', 'Flutter', 'Generated.xcconfig'), __FILE__)
  unless File.exist?(generated_xcode_build_settings_path)
    raise "#{generated_xcode_build_settings_path} must exist. If you're running pod install manually, make sure flutter pub get is executed first"
  end

  File.foreach(generated_xcode_build_settings_path) do |line|
    matches = line.match(/FLUTTER_ROOT\=(.*)/)
    return matches[1].strip if matches
  end
  # This should never happen...
  raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Generated.xcconfig, then run flutter pub get"
end

1、File.foreach读取文件的每一行并执行一个block。File.readlines读取文件的每一行到一个数组里面。
2、line.match匹配结果是个数组，包括两部分：0完整匹配部分、1匹配到的内容

总结：该方法，解析Flutter/Generated.xcconfig文件，遍历每一行，找到FLUTTER_ROOT的值并返回。

总结：该文件主要有三个方法：install_flutter_engine_pod、install_flutter_plugin_pods、install_flutter_application_pod。分别作用是：不存在就新生成并pod进来engine/Flutter.framework/flutter、pod进来FlutterPluginRegistrant+plugins、不存在就新生成app.framework/app并pod进来my_flutter。

思考：

1、更改flutter工程的dart代码，重新运行iOS工程(不是Runner),为什么代码能生效？
pod install的时候，执行了podhelper.rb，执行了install_flutter_application_pod方法，给target添加了编译前shell脚本。所以pod install 过后，每次运行iOS工程都会执行xcode_backend.sh build命令。