egeniq/injectpropertywrapper

Swift @Inject Property Wrapper

InjectPropertyWrapper

Provides a generic Swift @Inject property wrapper that can be used to inject objects / services from a dependency injection framework of your choice.

Basic Usage

First, you need to implement the Resolver protocol for the Dependency Injection (DI) framework you are using.

For example, when using Swinject:

extension Container: InjectPropertyWrapper.Resolver {
}

In case of Swinject the Container class already contains a method with the same signature (resolve<T>(_ type: T, name: String?)) as the InjectPropertyWrapper Resolver protocol requires.

Then you need to set the global resolver (for example in your app delegate):

let container = Container()
InjectSettings.resolver = container

Register some objects in the container:

container.register(APIClient.self) { _ in APIClient() }
container.register(MovieRepository.self) { _ in IMDBMovieRepository() }
container.register(MovieRepository.self, name: "netherlands") { _ in IMDBMovieRepository("nl") }

Now you can use the @Inject property wrapper to inject objects/services in your own classes:

class IMDBMovieRepository: MovieRepository {
    @Inject private var apiClient: APIClient
    
    ...
    
    func fetchTop10(completionHandler: @escaping (movies: [Movie]) -> Void) {
        ...
    }
}

class MovieViewModel: BindableObject {
    public var didChange = PassthroughSubject<Void, Never>()
    public private(set) var top10: [Movie]? {
        didSet {
            didChange.send()    
        }
    }

    @Inject private var movieRepository: MovieRepository
    
    func load() {
        movieRepository.fetchTop10() { [weak self] movies in
            self?.top10 = movies
        }
    }
}

It is also possible to inject different objects of the same type using the name parameter:

class MovieViewModel: BindableObject {
    ...
    @Inject private var globalMovieRepository: MovieRepository
    @Inject(name: "netherlands") private var nlMovieRepository: MovieRepository
    ...
}

Normally if the property wrapper is unable to resolve a dependency it will raise a non-recoverable fatal error. If for some reason you expect an object sometimes to be unavailable in your container, you can mark the property as optional:

class MovieViewModel: BindableObject {
    ...
    @Inject(name: "germany") private var deMovieRepository: MovieRepository?
    ...
}

Testing

To run the tests for this package make sure the ENABLE_TESTS environment variable is set to 1 or true. For example when using the command line:

ENABLE_TESTS=1 swift test

This allows the package to only load certain dependencies when testing.

License

This project is licensed under the terms of the MIT license. See the LICENSE file.

injectpropertywrapper's Issues

Optional dependency can not be resolved.

When registering an optional property, it can not be resolved by the property wrapper even when it's available (not nil).

Example:

class Foo {
    
    @Inject var bar: Int?
    
}

container.register(Int?.self) { _ in
    return 42
}.inObjectScope(.container)

From the docs I assume this should be supported and I have also seen an init created for Optionals, however that init is not used. I am not sure I fully understand the rationale behind how this generic init (on line 28) is supposed to work, but I believe for optional properties to resolve properly, the wrappedValue should be of an optional type as well or the Wrapped type should be passed as an argument to the generic init method, otherwise it is not used anywhere in the method body.

Looking forward to your reply, thanks.