在Podfile里尝试指定Flutter pod库的版本

在终端执行pod search Flutter，会发现Flutter在CocoaPods里其实有多个版本，但是，默认情况下，只会选择1.0.0

所以我就在想，是否能由我们自己决定用哪个Flutter pod库的版本呢？

经过一番尝试，终于成功指定了Flutter pod库的版本，但是这个方案并未在正式的项目里使用，只是我个人的一次尝试

分析Podfile

pod库的版本是在Podfile里配置的，所以这个时候，先分析一下Podfile

# 省略大部分Podfile代码，只看target的
target 'Runner' do
  use_frameworks!
  use_modular_headers!

  flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
end

根据将Flutter module集成到iOS项目里关于使用 CocoaPods 和 Flutter SDK集成

猜测关键代码是flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))

然后通过ruby的print语句(由于CocoaPods是由ruby实现的)找到了File.dirname所返回的路径就是项目目录下的ios

之后根据Podfile里target上面的一段代码，方法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
  raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Generated.xcconfig, then run flutter pub get"
end

require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelper'), flutter_root)

分析到一个文件路径flutter/packages/flutter_tools/bin/podhelper(这个flutter就是Flutter SDK存放路径，即环境变量FLUTTER_HOME指定的路径)，打开这个文件可以看到很多代码。通过搜索Flutter找到以下代码

  # Generate a fake podspec to represent the Flutter framework.
  # This is only necessary because plugin podspecs contain `s.dependency 'Flutter'`, and if this Podfile
  # does not add a `pod 'Flutter'` CocoaPods will try to download it from the CocoaPods trunk.
  File.open(copied_podspec_path, 'w') { |podspec|
    podspec.write <<~EOF
      #
      # NOTE: This podspec is NOT to be published. It is only used as a local source!
      #       This is a generated file; do not edit or check into version control.
      #

      Pod::Spec.new do |s|
        s.name             = 'Flutter'
        s.version          = '1.0.0'
        s.summary          = 'High-performance, high-fidelity mobile apps.'
        s.homepage         = 'https://flutter.io'
        s.license          = { :type => 'MIT' }
        s.author           = { 'Flutter Dev Team' => 'flutter-dev@googlegroups.com' }
        s.source           = { :git => 'https://github.com/flutter/engine', :tag => s.version.to_s }
        s.ios.deployment_target = '9.0'
        # Framework linking is handled by Flutter tooling, not CocoaPods.
        # Add a placeholder to satisfy `s.dependency 'Flutter'` plugin podspecs.
        s.vendored_frameworks = 'path/to/nothing'
      end
    EOF
  }

  # Keep pod path relative so it can be checked into Podfile.lock.
  pod 'Flutter', :path => 'Flutter'

尝试修改s.version = '1.0.0'为s.version = '2.0.2'再执行pod install

成功了

这里只修改了iOS部分，其实文件里还有macOS部分，也是直接修改s.version就可以了

指定podhelper的路径

经过一番折腾，终于找到了关键的podhelper.rb文件，但这个文件在Flutter SDK里，修改了，以后所有项目都有生效，那是否能只对当前项目有效呢？通过之前的分析，发现其实可以通过修改Podfile文件里的路径，就可以指定podhelper的路径

首先，我将flutter/packages/flutter_tools/bin/podhelper.rb拷贝到当前项目目录下的ios目录，和Podfile是同级的

然后修改Podfile的内容，内容如下

# Uncomment this line to define a global platform for your project
# platform :ios, '9.0'

# CocoaPods analytics sends network stats synchronously affecting flutter build latency.
ENV['COCOAPODS_DISABLE_STATS'] = 'true'

project 'Runner', {
  'Debug' => :debug,
  'Profile' => :release,
  'Release' => :release,
}

# 将flutter_root方法的代码移除，这个只是用来返回Flutter SDK路径的

# 这句是核心，这个是加载podhelper的路径
require File.expand_path(File.join('podhelper'))

flutter_ios_podfile_setup

target 'Runner' do
  use_frameworks!
  use_modular_headers!

  flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
end

post_install do |installer|
  installer.pods_project.targets.each do |target|
    flutter_additional_ios_build_settings(target)
  end
end

然后执行pod install，发现报错了，原来光修改Podfile是不行的，这样会导致podhelper.rb里的路径不对，所以还要对当前项目目录下ios里的podhelper.rb进行修改

在podhelper.rb里搜索artifacts_dir =

artifacts_dir = File.join('..', '..', '..', '..', 'bin', 'cache', 'artifacts', 'engine')
# 将上面这句代码修改为下面这样
artifacts_dir = File.expand_path(File.join('bin', 'cache', 'artifacts', 'engine'),flutter_root)

# 同时加入flutter_root方法加入到podhelper.rb里flutter_additional_ios_build_settings方法之前

搜索artifacts_dir =其实有两个结果，一个是iOS的，一个是macOS的，大家按需修改或者两个都改好也可以

放上我修改好的Podfile和podhelper.rb供大家参考，传送门

版本环境

Flutter已经迭代到2.5.3了，我的这次尝试未必适合所有版本

以下是我的环境

macOS Big Sur (11.6.1)
Xcode Version 12.5.1 (12E507)

Flutter 2.5.3 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 18116933e7 (2 weeks ago) • 2021-10-15 10:46:35 -0700
Engine • revision d3ea636dc5
Tools • Dart 2.14.4

pod --version
1.11.2

ruby --version
ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin20]

gem --version
3.0.3