Modular Architecture on iOS

iOS Project implemented with Modular Architecture. (Can be used as Template project by replacing item name “Movie”). More information in medium post: Medium Post about Modular Architecture

More information in medium post: Medium Post

Including Authentication module (initial scaling)

Modules Dependencies with Authentication

More information in medium post: Medium Post

How it can scale:

Check medium post for more information: Medium Post

Video 1: Extracting Networking Service Module. see steps

Video 2: Extracting Movies Search Feature Module. see steps

Requirements:

Xcode Version 11.2.1+ Swift 5.0+ CocoaPods 1.8.4+

Steps to create module

Step 1. Setup App project with CocoaPods: (Video 1 00:06)
- Open Terminal and change directory cd to folder with your project App.xcodeproj file, and execute following commands:
  - pod init
  - inside Podfile
    - uncomment platform :ios, '9.0', and change '9.0' to 14.0 or 15.0
    - add line: workspace 'AppName.xcworkspace'
    - add line: project 'AppName.xcodeproj'
  - pod install
Step 2. Create new Module with CocoaPods: (Video 1 00:48)
- In the same folder from previous step create a new folder with name DevPods:
  - mkdir DevPods
- Create New Module inside DevPods folder:
  - cd DevPods
  - pod lib create ModuleName
  - with Platform: iOS; Language: Swift; Include a Demo App: Yes; Test framework and view based testing we can skip
  Note: To use your own pod-template you can add the parameter --template-url=URL where URL is the git repo containing a compatible template.
Step 3. The Module's Example Demo project will be opened automatically, we need to update iOS and Swift versions: (Video 1 01:27)
- Select example project and set In Deployment Info to iOS 14.0 or iOS 15.0
- In Build Settings search for Swift and set Swift Language Version to Swift 5.
- Remove Test Target and Test folder inside the project
- Close this demo example project (otherwise you will not be able to open it from App.xcworkspace)
Step 4. Cleaning up DevPods/ModuleName folder: (Video 1 01:48)
- Show hidden files with Cmd + Shift + . and delete files: .git, .gitignore and .travis.yamls
- Delete files: _Pod.xcodeproj, Example/Podfile, Example/Podfile.lock, Example/Pods, Example/ModuleName.xcworkspace

Step 5. Edit Podfile of project located in same folder as app's project App.xcworkspace file: (Video 1 02:10)

Add module_name_pod inside Podfile:

 def module_name_pod
     pod 'ModuleName', :path => 'DevPods/ModuleName'
 end

Move nested test targets outside target 'App':

 target 'App' do
 ...
 end

 target 'AppTests' do
 	inherit! :search_paths
 end
 
 target 'AppUITests' do
 end

Add module's example target so we can develop this module from same main App's workspace:

 target 'ModuleName_Example' do
 	use_frameworks!
 	project 'DevPods/ModuleName/Example/ModuleName.xcodeproj'
 	
 	module_name_pod
 end

Step 6. Move files from main App into Module's Pod: (Video 1 03:14)
- Inside DevPods/ModuleName/ModuleName folder remove Assets and Classes folders and create folder with name Module.
- Move from main App to the Module folder all module's files (e.g. .swift, .xcassets, .storyboard, .xcdatamodeld...). After moving them from main App do not forget to delete them also from main App's target. For moving files is better to not use Xcode, and do it manually or with terminal.
  - Edit ModuleName.podspec:
    - Set ios deployment target: s.ios.deployment_target = '14.0' or 15.0
    - Replace s.source_files = ... to: (Video 1 03:53)
      s.source_files = 'MoviesSearch/Module/**/*.{swift}' s.resources = "MoviesSearch/Module/**/*.{xcassets,json,storyboard,xib,xcdatamodeld}"
      Note: if you have Core Data model with xcdatamodel extension you will need to convert it into xcdatamodeld by selecting this file and Editor or Help -> Add Model Version..
      
      Note: when you create new Group inside Development Pods/ModuleName with Xcode, it places its folder in wrong place outside of Module (pod folder). And it needs to be moved manually into Module folder using Finder, and then pod install

Step 7. Add all internal or external dependencies for this module. Add them inside ModuleName.podspec file located inside DevPods/ModuleName folder: (Video 2 03:33)

  # internal dependency (module you have created before)
  s.dependency 'ModuleName2' 

  # external dependency 3rd party framework 
  s.dependency 'PromiseKit'

Note: If you have not yet extracted your dependency and you need it here you can delegate this functionality to main App. Just create interface using protocol and implement it inside your main App. For example if you need to open chat from your module, then create protocol interface inside your module with function openChat(forUserId:inView:) and then implement it inside main App, and it will be injected from main App into DIContainer of the module. Also closures or delegation can be used.

Step 8. After pod install and compiling main App we will see some errors that we have to fix: (Video 2 03:45)

Inside main app, add import ModuleName in all files where it is needed
Change to public all types or functions that needs to be accessed from outside of the module, from main app or other module

Change all resources initialisers to initialise them with module's bundle (e.g. images, storyboards, nibs or CoreData models xcdatamodeld): (Video 2 05:15)

// Image load from bundle
UIImage(named: "image_name", in: Bundle(for: Self.self), compatibleWith: nil)
// Image Literal
final class LiteralBundleImage: _ExpressibleByImageLiteral {
	let image: UIImage?
	required init(imageLiteralResourceName name: String) {
		image = UIImage(named: name, in: Bundle(for: Self.self), compatibleWith: nil)
	}
}
let image = (#imageLiteral(resourceName: "image_name") as LiteralBundleImage)

// Storyboards and Nibs load from bundle
UIStoryboard(name: "name", bundle: Bundle(for: Self.self))
UINib(nibName: "name", bundle: Bundle(for: Self.self))

// Core Data model load from bundle
guard let modelURL = Bundle(for: Self.self).url(forResource: "ModelFileName", withExtension: "momd"),
      let mom = NSManagedObjectModel(contentsOf: modelURL)
      else {
            fatalError("Unable to located Core Data model")
}
let container = NSPersistentContainer(name: "Name", managedObjectModel: mom)

    Note: the file must have .xcdatamodeld extension, to convert it from xcdatamodel extension just Add Model Version..

Step 9. Move Module's tests from main App into module's Pod: (Video 2 07:20)
- Crete folder with name Tests inside DevPods/ModuleName/ModuleName/
- Move all files with tests from main App folder to DevPods/ModuleName/ModuleName/Tests. Note: Move them manually or using terminal, avoid doing it directly with Xcode groups.
- Add to ModuleName.podspec:
```
s.test_spec 'Tests' do |test_spec|
    test_spec.source_files = 'ModuleName/Tests/**/*.{swift}'
end
```
- Add to main App's Podfile module's pod , :testspecs => ['Tests']
```
def module_name_pod
	pod 'ModuleName', :path => 'DevPods/ModuleName', :testspecs => ['Tests']
end
```
  - Add to all unit tests files imports: @testable import ModuleName
  - Run in terminal pod install for main App Podfile
  - To make our Module's unit test app to run unit test with Cmd + U from main App schema:
  - Edit schema ModuleName-Example, inside Test section, add unit tests from Pod: under Pod -> ModuleName-Unit-Tests
Step 10. Fix ModuleName-Example schema used for developing module in isolation: (Video 2 09:45)
- Switch from main App schema to ModuleName-Example schema and try to build
- Note: AppDelegate method will have some warning and error that we have to fix, you can just copy paste it form main App
Step 11. To make our Module's Example app to run unit test with Cmd + U, we follow the same step as we did for main App: (Video 2 10:10)
- Edit schema ModuleName-Example, inside Test section, add unit tests from Pod: under Pod -> ModuleName-Unit-Tests

Module as Static Library [Optional]:

Change your modules to be as Static Libraries (We made it as Dynamic Library in previous steps):
- Remove from main App's Podfile: use_frameworks!
- Replace s.resources with s.resource_bundles in all modules' .podspec files (ModuleName.podspec):
  Note: resource_bundles has different structure: 'ModuleName' => [ ... ], where 'ModuleName' is bundle name:
```
s.resources = 'ModuleName/Module/**/*.{xcassets,json,storyboard,xib,xcdatamodeld}'
```
  Replace s.resources with:
```
s.resource_bundles = {
	'ModuleName' => ['ModuleName/Module/**/*.{xcassets,json,storyboard,xib,xcdatamodeld}']
}
```
- Replace all Bundle(for: Self.self) appearances with call to extension: Bundle(for: Self.self).resource
```
 extension Bundle {
     var resource: Bundle {
        return Bundle(url: resourceURL!.appendingPathComponent("ModuleName.bundle"))!
     }
 }
```
- If you have CoreData inside a module then open .xcdatamodeld file and change Codegen to Manual/None and Create NSManagedObject Subclass.. for all entities

Module's Testing in CI/CD [Optional]:

To keep always our modules buildable we need to build and run tests for each module on our Pipeline in CI. As example we can use Fastlane and Travis CI:

Fastlane script

 lane :test do |options|
 
   # Check if all modules are buildable
   all_modules_schemes.each do |s|
     UI.message "Testing if module #{s} is buildable"
     scan(
       scheme: s,
       device: simulator,
       build_for_testing: true,
     )
   end
 	
   # Run all unit and UI tests, and test if App is buildable
   scan(
     scheme: "App",
     device: simulator,
   )
 	
 end

Travis CI script

 os: osx
 osx_image: xcode11.2
 language: swift
 script:
 - fastlane test