Deli: an easy-to-use Dependency Injection Container that creates DI containers

by iOS Example

Deli is an easy-to-use Dependency Injection Container that creates DI containers with all required registrations and corresponding factories.

Language Switch: English, 한국어.

Overview

Wanna spaghetti? or not.
As your project grows, will experience a complex. We can write the wrong code by mistake.

In Spring framework provides automatic registration using some code rules and throws the wrong Dependency Graph before running. I wanted these features to be in Swift.

Getting Started

Simple setup for the automated configuration files, deli.yml.

If the configuration file does not exist, find the build target for a unique project in the current folders automatically. It works the same even if no scheme, target and output field is specified.

target:
  - MyProject

config:
  MyProject:
    project: MyProject
    scheme: MyScheme
    include:
      - Include files...
    exclude:
      - Exclude files...
    className: DeilFactory
    output: Sources/DeliFactory.swift
    resolve:
      output: Deli.resolved
      generate: true
    dependencies:
      - path: Resolved files...
        imports: UIKit
    accessControl: public

You’ll have to make your scheme Shared. To do this Manage Schemes and check the Shared areas:

Alternatively, you can specify target instead of scheme. In this case, Deli will find the Build Target.

Then build with the provided binaries.

$ deli build

Dependency Graph is configured through source code analysis. It is saved as the file you specified earlier.

File contents as below:

//
//  DeliFactory.swift
//  Auto generated code.
//

import Deli

final class DeliFactory: ModuleFactory {
    override func load(context: AppContextType) {
        ...
    }
}

Add the generated file to the project and call it from the app's launch point.

AppDelegate.swift:

import UIKit
import Deli

class AppDelegate {
    
    var window: UIWindow?

    let context = AppContext.load([
        DeliFactory.self
    ])

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        return true
    }
}

Build Phases

Integrate Deli into an Xcode scheme to get warnings and errors displayed in the IDE.
Just add a new "Run Script Phase" with:

if which deli >/dev/null; then
  deli build
else
  echo "error: Deli not installed, download from https://github.com/kawoou/Deli"
fi

Alternatively, if you've installed Deli via CocoaPods the script should look like this:

"${PODS_ROOT}/DeliBinary/deli" build

Features

1. Component

The class, struct, and protocol can extend the Component protocol and will be registered automatically in the DI container.

Component can be used as below:

protocol UserService {
    func login(id: String, password: String) -> User?
    func logout()
}

class UserServiceImpl: UserService, Component {
    func login(id: String, password: String) -> User? {
        ...
    }
    func logout() {
        ...
    }

    init() {}
}

If the above code is written, you can use the UserService or UserServiceImpl type to load the dependency instance.

2. Autowired

The Autowired protocol is registered automatically, same as Component protocol. A difference, you can load the required dependencies from DI container.

Autowired can be used as below:

class LoginViewModel: Autowired {
    let userService: UserService

    required init(_ userService: UserService) {
        self.userService = userService 
    }
}

Easy right? So let's look at the code below.

protocol Book {
    var name: String { get }
    var author: String { get }
    var category: String { get }
}

class Novel: Book {
    var qualifier: String {
        return "Novel"
    }

    var name: String {
        return ""
    }
    
    var author: String {
        return ""
    }
    
    var category: String {
        return "Novel"
    }
}

class HarryPotter: Novel, Component {
    override var name: String {
        return "Harry Potter"
    }
    
    override var author: String {
        return "J. K. Rowling"
    }
}

class TroisiemeHumanite: Novel, Component {
    override var name: String {
        return "Troisième humanité"
    }
    
    override var author: String {
        return "Bernard Werber"
    }
}

This code arranged the books through inheritance. You can get all of Book instances like below:

class LibraryService: Autowired {
    let books: [Book]

    required init(_ books: [Book]) {
        self.books = books
    }
}

Furthermore, What should do to get the books with the "Novel" qualifier?
In Deli, can be constructor injection in the below:

class LibraryService: Autowired {
    let books: [Book]

    required init(Novel books: [Book]) {
        self.books = books
    }
}

3. LazyAutowired

If we can remove whole Circular Dependency cases, the world will be better than before, but it cannot be ruled completely.
A simple way to solve this problem is to initialize one of the dependency lazily.

Let's try LazyAutowired protocol:

class UserService: Autowired {
    let messageService: MessageService

    required init(_ messageService: MessageService) {
        self.messageService = messageService
    }
}
class FriendService: Autowired {
    let userService: UserService

    required init(_ userService: UserService) {
        self.userService = userService
    }
}
class MessageService: Autowired {
    let friendService: FriendService

    required init(_ friendService: FriendService) {
        self.friendService = friendService
    }
}

If you try to inject a MessageService, Circular Dependency will occurred.

$ deli validate

Error: The circular dependency exists. (MessageService -> FriendService -> UserService -> MessageService)

What if UserService extends LazyAutowired?

class UserService: LazyAutowired {
    let messageService: MessageService!

    func inject(_ messageService: MessageService) {
        self.messageService = messageService
    }

    required init() {}
}

The cycle was broken and the issue was resolved!
After MessageService instance successfully created, dependencies can be injected via inject() that UserService needed.

In addition, LazyAutowired can be specified qualifier like Autowired.
Below code injects a UserService instance with the "facebook" qualifier specified:

class FacebookViewModel: LazyAutowired {
    let userService: UserService!

    func inject(facebook userService: UserService) {
        self.userService = userService
    }

    required init() {}
}

4. Configuration

The Configuration protocol makes the user can register Resolver directly.

Let's look at the code:

class UserConfiguration: Configuration {
    let networkManager = Config(NetworkManager.self, ConfigurationManager.self) { configurationManager in
        let privateKey = "1234QwEr!@#$"
        return configurationManager.make(privateKey: privateKey)
    }

    init() {}
}

You can see privateKey is passed to ConfigurationManager on NetworkManager creation.

This NetworkManager instance is registered in DI container, and it will be managed as singleton.
(However, instance behavior can be changed by updating scope argument.)

5. Inject

As written, Autowired is registered in DI container. But you may want to use without registration. That's an Inject.

class LoginView: Inject {
    let viewModel = Inject(LoginViewModel.self)

    init() {}
}

class NovelBookView: Inject {
    let novels: [Book] = Inject([Book].self, qualifier: "Novel")

    init() {}
}

6. Factory

In the front-end, often dynamically generating a model using the user's data. Let's take an example.

You must implement a friend list. When you select a cell from friends list, you need to present modal view of friend's information.
In this case, The friend data must be passed in the Info Modal.

This happens very often, Factory will help them.

Let's try AutowiredFactory protocol:

class FriendPayload: Payload {
    let userID: String
    let cachedName: String
    
    required init(with argument: (userID: String, cachedName: String)) {
        userID = argument.userID
        cachedName = argument.cachedName
    }
}

class FriendInfoViewModel: AutowiredFactory {
    let accountService: AccountService
    
    let userID: String
    var name: String
    
    required init(_ accountService: AccountService, payload: FriendPayload) {
        self.accountService = accountService
        self.userID = payload.userID
        self.name = payload.cachedName
    }
}

To pass a user-argument, you must implement a Payload protocol.
(Naturally, factories work by prototype scope)

Implemented FriendInfoViewModel can be used as below:

class FriendListViewModel: Autowired {
    let friendService: FriendService
    
    func generateInfo(by id: String) -> FriendInfoViewModel? {
        guard let friend = friendService.getFriend(by: id) else { return nil }
        
        return Inject(
            FriendInfoViewModel.self,
            with: (
                userID: friend.id,
                cachedName: friend.name
            )
        )
    }
    
    required init(_ friendService: FriendService) {
        self.friendService = friendService
    }
}

Next LazyAutowiredFactory protocol:

class FriendInfoViewModel: LazyAutowiredFactory {
    var accountService: AccountService!
    
    func inject(facebook accountService: AccountService) {
        self.accountService = accountService
    }
    
    required init(payload: TestPayload) {
        ...
    }
}

The difference between an AutowiredFactory and a LazyAutowiredFactory is that it is lazy injected with the relationship between Autowired and LazyAutowired.
However, payload injects by the constructor because passed by the user.

7. ModuleFactory

When injecting the dependency, required blueprint.
As above, This blueprint is generated at build(ex. DeliFactory).
When calling AppContext#load(), load container of generated class that inherited ModuleFactory.

Deli supports Multi-Container.
Can be used ModuleFactory as below.

7.1. Multi-Container

When calling AppContext#load(), also load the ModuleFactory in the module.

Can specify LoadPriority in this situation. This is the order for selecting the container to be used in dependency injection.

Priority are normal(500) defaultly. Container's order for selecting as below:

  1. High priority first.
AppContext.shared.load([
    OtherModule.DeliFactory.self,
    DeliFactory.self
])
  1. If priority is same, In the loaded order.
AppContext.shared
    .load(DeliFactory())
    .load(OtherModule.DeliFactory(), priority: .high)

7.2. Unit Test

Priority loading that same as 7.1 used be Unit Test, too.

import Quick
import Nimble

@testable import MyApp

class UserTests: QuickSpec {
    override func spec() {
        super.spec()

        let testModule: ModuleFactory!
        testModule.register(UserService.self) { MockUserService() }

        let appContext = AppContext.shared
        beforeEach {
            appContext.load(testModule, priority: .high)
        }
        afterEach {
            appContext.unload(testModule)
        }
        
        ...
    }
}

An example of a test code is Deli.xcodeproj.

8. Struct

Support for Struct has been added since version 0.7.0.

The basic behavior is the same as Class, but one difference is that cannot use weak Scope.

Below is an example of Moya's plugin implementation.

struct AuthPlugin: PluginType, LazyAutowired {

    var scope: Scope = .weak

    private let authService: AuthService!

    func prepare(_ request: URLRequest, target: TargetType) -> URLRequest {
        var request = request

        if let authToken = authService.authToken {
            request.addValue(authToken.accessToken, forHTTPHeaderField: "Authorization")
            request.addValue(authToken.refreshToken, forHTTPHeaderField: "Refresh-Token")
        }

        return request
    }

    mutating func inject(_ authService: AuthService) {
        self.authService = authService
    }

    init() {}
}

9. Configuration Property

It's often profit to use different configuration values depending on the running environment.
For example, you can specific that save the file log at development build and not save the file log at the Release build.

application-dev.yml:

logger:
    storage: file

server:
    url: https://dev.example.com/api
    isDebug: false

application-prod.yml:

logger:
    storage: default

server:
    url: https://www.example.com/api
    isDebug: true

9.1. Usage

Two ways solution to use the Configuration Property created above.

  1. Change deli.yml.
  2. Modify the build script

Change the configuration file as below:

target:
- MyApp

config:
  MyApp:
    - project: MyApp
    - properties:
      - Configurations/Common/*.yml
      - Configurations/application-dev.yml

Build script can do this:

deli build \
  --property "Configurations/Common/*.yml" \
  --property "Configurations/application-dev.yml"

If the same configuration information, it's overwritten with the last specified information.

9.2. Group Value

You can use ConfigProperty to safe retrieve the specified value in the configuration file.

struct ServerConfig: ConfigProperty {
    let target: String = "server"

    let url: String
    let isDebug: Bool
}

When implementing the model as above, ServerConfig is registered in IoC Container.

One thing to keep in mind when defining the model, need to set the target value. This property represents the path to retrieve in the configuration file using JSONPath style.

If you do not have the required configuration values at build time, will occurred a compile error.

final class NetworkManager: Autowired {
    let info: ServerConfig

    required init(_ config: ServerConfig) {
        info = config
    }
}

9.3. Single Value

When get a bundle value as above, implement the ConfigProperty protocol. So how to get a single value? You can use the InjectProperty.

final class NetworkManager: Inject {
    let serverUrl = InjectProperty("server.url")
}

InjectProperty is similar to ConfigProperty. It checks the configuration value at build time and inject data as String type.

If you want to retrieve configuration value optionally without validation, this is not a proper way.

In this case, recommend using the AppContext#getProperty() method.

final class NetworkManager {
    let serverUrl = AppContext.getProperty("server.url", type: String.self) ?? "https://wtf.example.com"
}

9.4. Qualifier by Property

To enhance usability of configuration property, Deli provides a way of injection using qualifier as configuration value.

There are two ways to use it. let's look first that constructor injection like Autowired.

As mentioned in the Autowired paragraph, you can not use . for parts that specify qualifier. Unfortunately, swift do not has an annotation-like features. So I implemented to use comment as an alternative.

How it works:

final class UserService: Autowired {
    required init(_/*logger.storage*/ logger: Logger) {
    }
}

When using the Inject method:

final class UserService: Inject {
    func getLogger() -> Logger {
        return Inject(Logger.self, qualifierBy: "logger.storage")
    }
}

10. PropertyWrapper

For easier use, supports the @propertyWrapper added in Swift 5.1.

There are two main features to be supported: dependency injection and Configuration Property.

10.1. Dependency

There are @Dependency and @DependencyArray for injection of dependencies.

class Library {
    @Dependency(qualifier "logger.storage")
    var logger: Logger

    @DependencyArray(qualifier: "novel")
    var novels: [Book]
}

10.2. PropertyValue

@PropertyValue is the same as Configuration Property and the usage as below:

final class NetworkManager: Inject {
    @PropertyValue("server.url")
    let serverUrl: String
}

Installation

Cocoapods:

Simply add the following line to your Podfile:

pod 'Deli', '~> 0.8.1'

Carthage:

github "kawoou/Deli"

Command Line

$ deli help
Available commands:

   build      Build the Dependency Graph.
   generate   Generate the Dependency Graph.
   help       Display general or command-specific help
   upgrade    Upgrade outdated.
   validate   Validate the Dependency Graph.
   version    Display the current version of Deli

Examples

Contributing

Any discussions and pull requests are welcomed.

If you want to contribute, submit a pull request.

Requirements

  • Swift 3.1+

Attributions

This project is powered by

License

Deli is under MIT license. See the LICENSE file for more info.

GitHub

https://github.com/kawoou/Deli