feat: One module for iOS and MacOS instead of two

[rekire]

Migrated from VeryGoodOpenSource/very_good_flutter_plugin#154

Description

There is a way to declare that you want to use the same code for iOS and MacOS. There was a proposal which explained it quite well. This is already in use e.g. for the path_provider package. Which this feature you can avoid a lot of duplicated code (I expect that you do the same on both platforms).

Requirements

• Rewrite the plugin to support that

Additional Context

Here is an example how the MyPlugin.swift should look like afterwards:

#if os(iOS)
import Flutter
#elseif os(macOS)
import FlutterMacOS
#endif

public class MyPlugin: NSObject, FlutterPlugin {
    public static func register(with registrar: FlutterPluginRegistrar) {
        // Workaround for https://github.com/flutter/flutter/issues/118103.
#if os(iOS)
        let messenger = registrar.messenger()
#else
        let messenger = registrar.messenger
#endif
        let channel = FlutterMethodChannel(
            name: "my_plugin_darwin",
            binaryMessenger: messenger)
        let instance = MyPlugin()
        registrar.addMethodCallDelegate(instance, channel: channel)
    }

//...

The podfile should look like this:

Pod::Spec.new do |s|
  s.name             = 'my_plugin_darwin'
  s.version          = '0.0.1'
  s.summary          = 'The iOS and MacOS implementation of my plugin.'
  s.description      = <<-DESC
  The iOS and MacOS implementation of the my plugin.
                       DESC
  s.homepage         = 'http://example.com'
  s.license          = { :type => 'BSD', :file => '../LICENSE' }
  s.author           = { 'Your Company' => 'email@example.com' }
  s.source           = { :path => '.' }
  s.source_files = 'Classes/**/*'

  s.swift_version = '5.0'

  s.ios.dependency 'Flutter'
  s.osx.dependency 'FlutterMacOS'
  s.ios.deployment_target = '11.0' # or what ever version you need
  s.osx.deployment_target = '11.0' # or what ever version you need
end

The my_plugin_darwin/pubspec.yaml like this:

flutter:
  plugin:
    implements: my_plugin
    platforms:
      ios:
        pluginClass: MyPlugin
        dartPluginClass: MyPluginDarwin
        sharedDarwinSource: true
      macos:
        pluginClass: MyPlugin
        dartPluginClass: MyPluginDarwin
        sharedDarwinSource: true

Those are of cause not all changes, but that should reflect the most relevant.