IOS Flutter混编工程的CI接入--原理篇

现在公司的绝大多数工程都是使用的iOS和Flutter混编来做的，其中混编的方式是采用的Google推荐的Module方式来做的。具体请参考将 Flutter module 集成到 iOS 项目-选项 A - 使用 CocoaPods 和 Flutter SDK 集成或者Integrate a Flutter module into your iOS project : Option A - Embed with CocoaPods and the Flutter SDK。 但是在这种混编工程中，即使只修改ios部分的代码，编译的时候也会花费一定的时间来编译Flutter工程，这就导致纯iOS的开发效率很低。那如何解决这个问题呢？
我们首先看一下Google提供的集成步骤：
1.在 Podfile 中添加下面代码：

flutter_application_path = '../my_flutter'
load File.join(flutter_application_path, '.ios', 'Flutter', 'podhelper.rb')

2. 每个需要集成 Flutter 的 [Podfile target][]，执行

`install_all_flutter_pods(flutter_application_path)`：

target 'MyApp' do
  install_all_flutter_pods(flutter_application_path)
end

也就是说在pod install过程中，会调用flutter_application_path/.ios/ Flutter/ podhelper.rb文件中的install_all_flutter_pods(flutter_application_path)这个方法来做一系列的操作。这个文件其实是从Flutter SDK中的模版文件拷贝过来的，具体可以查看podhelper.rb.tmpl。

我们看一下install_all_flutter_pods方法：

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

其实主要步骤就是：

1. 在podFile中指定flutter_engine的pod库地址：
   也就是在podfile中加入
   pod 'Flutter', :path => relative.to_s, :inhibit_warnings => true，其中relative.to_s就是方法中需要指定的地址。

def install_flutter_engine_pod
  engine_dir = File.join(__dir__, 'engine')
  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
  project_directory_pathname = Pathname.new Dir.pwd
  relative = engine_pathname.relative_path_from project_directory_pathname

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

2.在podFile中指定flutter_plugin的pod库地址：
读取Flutter工程目录下的.flutter-plugins文件，读取你所引用的所有plugin，然后逐个加入到podfile中。

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 __dir__
  project_directory_pathname = Pathname.new Dir.pwd
  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)
  plugin_pods = parse_KV_file(File.join(flutter_application_path, '.flutter-plugins'))
  plugin_pods.map do |r|
    symlink = File.join(symlinks_dir, r[:name])
    FileUtils.rm_f(symlink)
    File.symlink(r[:path], symlink)
    pod r[:name], :path => File.join(symlink, 'ios'), :inhibit_warnings => true
  end
end

.flutter-plugins文件示例

3.在podFile中指定flutter_application的pod库地址：
也就是在podfile中加入
pod 'flutter_xxx_xxx', :path => relative.to_s, :inhibit_warnings => true，其中relative.to_s就是方法中需要指定的地址。
然后在Xcode的build Phase中增加一个Flutter Build Script的过程，这个过程中执行的脚本是FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh。

def install_flutter_application_pod(flutter_application_path)
  app_framework_dir = File.join(__dir__, 'App.framework')
  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.
  current_directory_pathname = Pathname.new __dir__
  project_directory_pathname = Pathname.new Dir.pwd
  relative = current_directory_pathname.relative_path_from project_directory_pathname
  pod 'flutter_xxx_xxx', :path => relative.to_s, :inhibit_warnings => true

  flutter_export_environment_path = File.join('${SRCROOT}', relative, 'flutter_export_environment.sh');
  script_phase :name => 'Run Flutter Build Script',
    :script => "set -e\nset -u\nsource \"#{flutter_export_environment_path}\"\n\"$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

因此整个流程也就变成，在podfile中加入flutter_engine(Flutter.framework)的pod库、flutter_plugin的pod库和flutter_application(App.framework)的pod库,然后编译整个flutter工程。

那如果我们现在想要将iOS工程与Flutter工程相隔离就需要改造整个流程。
原来的流程：在podfile中加入所有的Flutter相关的Pod库--编译Flutter工程产出相关的Pod库文件--编译iOS工程。

ios_flutter_origin.jpg

那既然每次编译以后，都会产出这三种产物，那我们在每次发布release包的时候获取这三种产物，然后把他们上传到git库中。然后在iOS工程中创建一个submodule，指向这个git库，然后修改podfile中的编译流程，修改这三种产物的pod库地址从Flutter工程相关的地址为本地的submoudle的地址，然后直接编译iOS工程即可，即避免了每次编译Flutter工程，又能做到iOS工程和Flutter工程的彻底隔绝。

ios_flutter_after.jpg

下一篇会详细讲一下如何在项目中进行实践。