Permalink
220 lines (185 sloc) 8.51 KB

Basic Usage

So how do you use this library? Well, it's pretty easy. Just follow this template. First, set up an enum with all of your API targets. Note that you can include information as part of your enum. Let's look at a common example. First we create a new file named MyService.swift:

enum MyService {
    case zen
    case showUser(id: Int)
    case createUser(firstName: String, lastName: String)
    case updateUser(id: Int, firstName: String, lastName: String)
    case showAccounts
}

This enum is used to make sure that you provide implementation details for each target (at compile time). You can see that parameters needed for requests can be defined as per the enum cases parameters. The enum must additionally conform to the TargetType protocol. Let's get this done via an extension in the same file:

// MARK: - TargetType Protocol Implementation
extension MyService: TargetType {
    var baseURL: URL { return URL(string: "https://api.myservice.com")! }
    var path: String {
        switch self {
        case .zen:
            return "/zen"
        case .showUser(let id), .updateUser(let id, _, _):
            return "/users/\(id)"
        case .createUser(_, _):
            return "/users"
        case .showAccounts:
            return "/accounts"
        }
    }
    var method: Moya.Method {
        switch self {
        case .zen, .showUser, .showAccounts:
            return .get
        case .createUser, .updateUser:
            return .post
        }
    }
    var task: Task {
        switch self {
        case .zen, .showUser, .showAccounts: // Send no parameters
            return .requestPlain
        case let .updateUser(_, firstName, lastName):  // Always sends parameters in URL, regardless of which HTTP method is used
            return .requestParameters(parameters: ["first_name": firstName, "last_name": lastName], encoding: URLEncoding.queryString)
        case let .createUser(firstName, lastName): // Always send parameters as JSON in request body
            return .requestParameters(parameters: ["first_name": firstName, "last_name": lastName], encoding: JSONEncoding.default)
        }
    }
    var sampleData: Data {
        switch self {
        case .zen:
            return "Half measures are as bad as nothing at all.".utf8Encoded
        case .showUser(let id):
            return "{\"id\": \(id), \"first_name\": \"Harry\", \"last_name\": \"Potter\"}".utf8Encoded
        case .createUser(let firstName, let lastName):
            return "{\"id\": 100, \"first_name\": \"\(firstName)\", \"last_name\": \"\(lastName)\"}".utf8Encoded
        case .updateUser(let id, let firstName, let lastName):
            return "{\"id\": \(id), \"first_name\": \"\(firstName)\", \"last_name\": \"\(lastName)\"}".utf8Encoded
        case .showAccounts:
            // Provided you have a file named accounts.json in your bundle.
            guard let url = Bundle.main.url(forResource: "accounts", withExtension: "json"),
                let data = try? Data(contentsOf: url) else {
                    return Data()
            }
            return data
        }
    }
    var headers: [String: String]? {
        return ["Content-type": "application/json"]
    }
}
// MARK: - Helpers
private extension String {
    var urlEscaped: String {
        return addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)!
    }

    var utf8Encoded: Data {
        return data(using: .utf8)!
    }
}

(The String extension is just for convenience – you don't have to use it.)

You can see that the TargetType protocol makes sure that each value of the enum translates into a full request. Each full request is split up into the baseURL, the path specifying the subpath of the request, the method which defines the HTTP method and task with options to specify parameters to be added to the request.

Note that at this point you have added enough information for a basic API networking layer to work. By default Moya will combine all the given parts into a full request:

let provider = MoyaProvider<MyService>()
provider.request(.createUser(firstName: "James", lastName: "Potter")) { result in
    // do something with the result (read on for more details)
}

// The full request will result to the following:
// POST https://api.myservice.com/users
// Request body:
// {
//   "first_name": "James",
//   "last_name": "Potter"
// }

provider.request(.updateUser(id: 123, firstName: "Harry", lastName: "Potter")) { result in
    // do something with the result (read on for more details)
}

// The full request will result to the following:
// POST https://api.myservice.com/users/123?first_name=Harry&last_name=Potter

Always remember to retain the provider somewhere: if you fail to do so, it will be released automatically, potentially before you receive any response.

The TargetType specifies both a base URL for the API and the sample data for each enum value. The sample data are Data instances, and could represent JSON, images, text, whatever you're expecting from that endpoint.

You can also set up custom endpoints to alter the default behavior to your needs. For example:

let endpointClosure = { (target: MyService) -> Endpoint in
    return Endpoint(url: URL(target: target), sampleResponseClosure: {.networkResponse(200, target.sampleData)}, method: target.method, task: target.task, httpHeaderFields: target.headers)
}

The block you provide will be invoked every time an API call is to be made. Its responsibility is to return an Endpoint instance configured for use by Moya.

Most of the time, this closure is just a straight translation from target, method and task into an Endpoint instance. However, since it's a closure, it'll be executed at each invocation of the API, so you could do whatever you want. Say you want to test network error conditions like timeouts, too.

let failureEndpointClosure = { (target: MyService) -> Endpoint in
    let sampleResponseClosure = { () -> (EndpointSampleResponse) in
        if shouldTimeout {
            return .networkError(NSError())
        } else {
            return .networkResponse(200, target.sampleData)
        }
    }
    return Endpoint(url: url(target), sampleResponseClosure: sampleResponseClosure, method: target.method, task: target.task, httpHeaderFields: target.headers)
}

Notice that returning sample data is required. One of the key benefits of Moya is that it makes testing the app or running the app using stubbed responses for API calls really easy.

Great, now we're all set. Just need to create our provider.

// Tuck this away somewhere where it'll be visible to anyone who wants to use it
var provider: MoyaProvider<MyService>!

// Create this instance at app launch
let provider = MoyaProvider(endpointClosure: endpointClosure)

Neato. Now how do we make a request?

provider.request(.zen) { result in
    // do something with `result`
}

The request method is given a MyService value (.zen), which contains all the information necessary to create the Endpoint – or to return a stubbed response during testing.

The Endpoint instance is used to create a URLRequest (the heavy lifting is done via Alamofire), and the request is sent (again - Alamofire). Once Alamofire gets a response (or fails to get a response), Moya will wrap the success or failure in a Result enum. result is either .success(Moya.Response) or .failure(MoyaError).

You will need to unpack the data and status code from Moya.Response.

provider.request(.zen) { result in
    switch result {
    case let .success(moyaResponse):
        let data = moyaResponse.data // Data, your JSON response is probably in here!
        let statusCode = moyaResponse.statusCode // Int - 200, 401, 500, etc

        // do something in your app
    case let .failure(error):
        // TODO: handle the error == best. comment. ever.
    }
}

Take special note: a .failure means that the server either didn't receive the request (e.g. reachability/connectivity error) or it didn't send a response (e.g. the request timed out). If you get a .failure, you probably want to re-send the request after a time delay or when an internet connection is established.

Once you have a .success(response) you might want to filter on status codes or convert the response data to JSON. Moya.Response can help!

See more at https://github.com/Moya/Moya/blob/master/Sources/Moya/Response.swift
do {
    try moyaResponse.filterSuccessfulStatusCodes()
    let data = try moyaResponse.mapJSON()
}
catch {
    // show an error to your user
}