iOS Networking Layer Architecture - ios

Reason For Post
There are so many different solutions & examples on how to build a proper networking layer, but every app has different constraints, and design decisions are made based on trade-offs, leaving me uncertain about the quality of code I've written. If there are any Anti-Patterns, redundancies, or flat out bad solutions within my code that I have overlooked or simply lacked the knowledge to address, please do critique. This is a project I'd like to add to my portfolio, so I'm posting it here to get eyes on it, with some advice/tips.
Thanks for your time in advanced!
Some characteristics of my networking layer that I think could raise eyebrows:
Method contains a GETALL case, to indicate a list of data that must be fetched. I have not seen this in any of the open source code I've read. Is this a code smell?
enum Method {
case GET
/// Indicates how JSON response should be handled differently to abastract a list of entities
case GETALL
case PUT
case DELETE
}
I've made it, so each Swift Entity conforms to JSONable protocol, meaning it can be initialized with json and converted to json.
protocol JSONable {
init?(json: [String: AnyObject])
func toJSON() -> Data?
}
JSONable in practice with one of my entities:
struct User {
var id: String
var name: String
var location: String
var rating: Double
var keywords: NSArray
var profileImageUrl: String
}
extension User: JSONable {
init?(json: [String : AnyObject]) {
guard let id = json[Constant.id] as? String, let name = json[Constant.name] as? String, let location = json[Constant.location] as? String, let rating = json[Constant.rating] as? Double, let keywords = json[Constant.keywords] as? NSArray, let profileImageUrl = json[Constant.profileImageUrl] as? String else {
return nil
}
self.init(id: id, name: name, location: location, rating: rating, keywords: keywords, profileImageUrl: profileImageUrl)
}
func toJSON() -> Data? {
let data: [String: Any] = [Constant.id: id, Constant.name: name, Constant.location: location, Constant.rating: rating, Constant.keywords: keywords, Constant.profileImageUrl: profileImageUrl]
let jsonData = try? JSONSerialization.data(withJSONObject: data, options: [])
return jsonData
}
}
This allows me to use generics to initialize all my entities in my client- FirebaseAPI, after I retrieve JSON response. I also haven't seen this technique in the code I've read.
In the code below, notice how GETALL is implemented to flatten the list of JSON objects. Should I have to do this at all? Is there a better way to handle any type of Json structure response?
AND Entities are initialized generically, and returned as an Observable ( Using RxSwift ).
Do you sense any code smells?
/// Responsible for Making actual API requests & Handling response
/// Returns an observable object that conforms to JSONable protocol.
/// Entities that confrom to JSONable just means they can be initialized with json & transformed from swift to JSON.
func rx_fireRequest<Entity: JSONable>(_ endpoint: FirebaseEndpoint, ofType _: Entity.Type ) -> Observable<[Entity]> {
return Observable.create { [weak self] observer in
self?.session.dataTask(with: endpoint.request, completionHandler: { (data, response, error) in
/// Parse response from request.
let parsedResponse = Parser(data: data, response: response, error: error)
.parse()
switch parsedResponse {
case .error(let error):
observer.onError(error)
return
case .success(let data):
var entities = [Entity]()
switch endpoint.method {
/// Flatten JSON strucuture to retrieve a list of entities.
/// Denoted by 'GETALL' method.
case .GETALL:
/// Key (underscored) is unique identifier for each entity
/// value is k/v pairs of entity attributes.
for (_, value) in data {
if let value = value as? [String: AnyObject], let entity = Entity(json: value) {
entities.append(entity)
}
}
/// Force downcast for generic type inference.
observer.onNext(entities as! [Entity])
//observer.onCompleted()
/// All other methods return JSON that can be used to initialize JSONable entities
default:
if let entity = Entity(json: data) {
observer.onNext([entity] as! [Entity])
//observer.onCompleted()
} else {
observer.onError(NetworkError.initializationFailure)
}
}
}
}).resume()
return Disposables.create()
}
}
}
I manage different endpoints like so:
enum FirebaseEndpoint {
case saveUser(data: [String: AnyObject])
case fetchUser(id: String)
case removeUser(id: String)
case saveItem(data: [String: AnyObject])
case fetchItem(id: String)
case fetchItems
case removeItem(id: String)
case saveMessage(data: [String: AnyObject])
case fetchMessages(chatroomId: String)
case removeMessage(id: String)
}
extension FirebaseEndpoint: Endpoint {
var base: String {
// Add this as a constant to APP Secrts struct & dont include secrets file when pushed to github.
return "https://AppName.firebaseio.com"
}
var path: String {
switch self {
case .saveUser(let data): return "/\(Constant.users)/\(data[Constant.id])"
case .fetchUser(let id): return "/\(Constant.users)/\(id)"
case .removeUser(let id): return "/\(Constant.users)/\(id)"
case .saveItem(let data): return "/\(Constant.items)/\(data[Constant.id])"
case .fetchItem(let id): return "/\(Constant.items)/\(id)"
case .fetchItems: return "/\(Constant.items)"
case .removeItem(let id): return "/\(Constant.items)/\(id)"
case .saveMessage(let data): return "/\(Constant.messages)/\(data[Constant.id])"
case .fetchMessages(let chatroomId): return "\(Constant.messages)/\(chatroomId)"
case .removeMessage(let id): return "/\(Constant.messages)/\(id)"
}
}
var method: Method {
switch self {
case .fetchUser, .fetchItem: return .GET
case .fetchItems, .fetchMessages: return .GETALL
case .saveUser, .saveItem, .saveMessage: return .PUT
case .removeUser, .removeItem, .removeMessage: return .DELETE
}
}
var body: [String : AnyObject]? {
switch self {
case .saveItem(let data), .saveUser(let data), .saveMessage(let data): return data
default: return nil
}
}
}
Last thing, I'd like someone with professional eyes to look at is, how I use MVVM. I make all network requests from view model, which comes out looking something like this:
struct SearchViewModel {
// Outputs
var collectionItems: Observable<[Item]>
var error: Observable<Error>
init(controlValue: Observable<Int>, api: FirebaseAPI, user: User) {
let serverItems = controlValue
.map { ItemCategory(rawValue: $0) }
.filter { $0 != nil }.map { $0! }
.flatMap { api.rx_fetchItems(for: user, category: $0)
.materialize()
}
.filter { !$0.isCompleted }
.shareReplayLatestWhileConnected()
collectionItems = serverItems.filter { $0.element != nil }.dematerialize()
error = serverItems.filter { $0.error != nil }.map { $0.error! }
}
}
In order to call api requests in a more expressive, formalized way, I am able to call api.rx_fetchItems(for:) inside flatmap above, because I extend FirebaseAPI to conform to FetchItemsAPI. I will probably have to follow the same pattern for most other requests.
extension FirebaseAPI: FetchItemsAPI {
// MARK: Fetch Items Protocol
func rx_fetchItems(for user: User, category: ItemCategory) -> Observable<[Item]> {
// fetched items returns all items in database as Observable<[Item]>
let fetchedItems = rx_fireRequest(.fetchItems, ofType: Item.self)
switch category {
case .Local:
let localItems = fetchedItems
.flatMapLatest { (itemList) -> Observable<[Item]> in
return self.rx_localItems(user: user, items: itemList)
}
return localItems
case .RecentlyAdded:
// Compare current date to creation date of item. If its within 24 hours, It makes the cut.
let recentlyAddedItems = fetchedItems
.flatMapLatest { (itemList) -> Observable<[Item]> in
return self.rx_recentlyAddedItems(items: itemList)
}
return recentlyAddedItems
case .Trending:
let trendingItems = fetchedItems
.flatMapLatest { (itemList) -> Observable<[Item]> in
return self.rx_trendingItems(items: itemList)
}
return trendingItems
default:
let stubItem = Item(id: "DEFAULT", createdById: "createdBy", creationDate: 1.3, expirationDate: 2.4, title: "title", price: 2, info: "info", imageUrl: "url", bidCount: 4, location: "LA")
return Observable.just([stubItem])
}
}
// MARK: Helper Methods
private func rx_localItems(user: User, items: [Item]) -> Observable<[Item]> {
return Observable<[Item]>.create { observer in
observer.onNext(items.filter { $0.location == user.location }) // LA Matches stubs in db
return Disposables.create()
}
}
func rx_recentlyAddedItems(items: [Item]) -> Observable<[Item]> {
return Observable<[Item]>.create { observer in
let recentItems = items
.filter {
let now = Date(timeIntervalSinceReferenceDate: 0)
let creationDate = Date(timeIntervalSince1970: $0.creationDate)
if let hoursAgo = now.offset(from: creationDate, units: [.hour], maxUnits: 1) {
return Int(hoursAgo)! < 24
} else {
return false
}
}
observer.onNext(recentItems)
return Disposables.create()
}
}
func rx_trendingItems(items: [Item]) -> Observable<[Item]> {
return Observable<[Item]>.create { observer in
observer.onNext(items.filter { $0.bidCount > 8 })
return Disposables.create()
}
}
}
I'm attempting to follow SOLID principles, and level up with RxSWift + MVVM, so I'm still unsure about the best OOP design for clean, maintainable code.

Related

Is there a workaround for Converting from <operationQuery.Data> to Data type?

Language:Swift
Hello, I'd like some help in resolving an error being thrown when I try to retrieve data from an Apollo GraphQL request that I'm making. The API in use is the AniList API utilizing GraphQL.
Here's what I've tried:
In my model I'm making the Apollo GraphQL query inside of a search() function. I want to then use the Codable protocol to fill an array of anime objects. Currently it's setup to return just for 1 anime object. I was planning on using this anime list as a data set for TableView later. I wanted to take small steps so my current goal is to at least get the Codable protocol to work and return the response data to an anime Struct object.
The documentation for Apollo shows how to get individual fields but when I try to get the corresponding fields from my response , I don't even have the option.
func search(){
Network.shared.apollo.fetch(query: AnisearchQuery()){ result in
guard let data = try? result.get().data else { return }
var topData:APIResponse?
do{
topData = JSONDecoder().decode(APIResponse.self, from: data.self)
}catch{
}
}
}
Here are the data structures that I've set up as a representation of the JSON data I expect to receive with respect to the hierarchy it is laid out in the response.
struct APIResponse:Codable{
let data:data
}
struct data:Codable{
let Page:page
let media:media
}
struct media:Codable{
let animeResults:anime
}
struct anime:Codable{
var romaji:String
var english: String
var native:String
var episodes:Int
var duration:Int
var medium:String
}
Here is the error in question.
"Cannot convert value of type 'AnisearchQuery.Data' to expected argument type 'Data'". This is generated by this line of code
topData = JSONDecoder().decode(APIResponse.self, from: data.self)
For further context , AnisearchQuery.Data is generated in response to the query I created for the codgen.
Here's what the data would look like in JSON format
This is the setup of the query:
query anisearch($page:Int, $perPage:Int, $search:String){
Page (page:$page, perPage:$perPage){
pageInfo {
total
currentPage
lastPage
hasNextPage
perPage
}
media(search:$search){
title{
romaji
english
native
}
episodes
duration
coverImage{
medium
}
}
}
}
Here's the Data object in the API.swift file:
public struct Data: GraphQLSelectionSet {
public static let possibleTypes: [String] = ["Query"]
public static var selections: [GraphQLSelection] {
return [
GraphQLField("Page", arguments: ["page": GraphQLVariable("page"), "perPage": GraphQLVariable("perPage")], type: .object(Page.selections)),
]
}
I'd be open to any alternative methods as to getting this task done or perhaps fixes to the error being thrown.
Many thanks in advance.
Inefficient Workaround
var animeCollection:SearchAnimeQuery.Data?
var media:[SearchAnimeQuery.Data.Page.Medium]?
var filteredData:[SearchAnimeQuery.Data.Page.Medium] = []
func loadData(search:String = "") {
if !search.isEmpty{
Network.shared.apollo.fetch(query: SearchAnimeQuery(search: search)){
[weak self] result in
//Make Sure ViewController Has not been deallocated
guard let self = self else{
return
}
/*defer {
}*/
switch result {
case .success(let graphQLResult):
if let animeData = graphQLResult.data {
DispatchQueue.main.async {
self.animeCollection = animeData
self.media = self.animeCollection?.page?.media as! [SearchAnimeQuery.Data.Page.Medium]
self.filteredData = self.media!
self.tableView.reloadData()
}
}
if let errors = graphQLResult.errors {
let message = errors
.map { $0.localizedDescription }
.joined(separator: "\n")
print(message)
}
case .failure(let error):
print(error.localizedDescription)
}
}
}
}

Cannot cast/decode data from server into Swift data model?

I need to cast the below response from my server as [UserResult] but I cannot get it to work??
What am I doing wrong?
func userSearch(keyword: String, completion: #escaping (Result<[UserResult], ResponseError>) -> Void ) {
socket.emit("userSearch", keyword)
socket.on("userFound") { ( data, ack) in
print(data) // prints below NSArray
if !data.isEmpty {
if let response = data as? [UserResult] {
print("USERS \(response)") // WILL NOT WORK?
completion(.success(response))
}
} else {
completion(.failure(.badRequest("No users found")))
}
}
}
Data from server
[<__NSArrayM 0x60000040e5b0>(
{
profileUrl = "www.address1.com";
username = chrissmith;
},
{
profileUrl = "www.address2.com";
username = johnsmith;
},
{
profileUrl = "www.address3.com";
username = alicesmith;
}
)
]
UserResult Model
struct UserResult: Decodable {
let username: String
let profileUrl: String
}
Well you are using Socket.IO library and specifically method
socket.on(clientEvent: .connect) {data, ack in
...
}
defined as
#discardableResult
open func on(clientEvent event: SocketClientEvent, callback: #escaping NormalCallback) -> UUID
using typealias:
public typealias NormalCallback = ([Any], SocketAckEmitter) -> ()
So basically at the and you are being returned data of type [Any] according to documentation.
Since you do not know what is inside your data it is better for you to unwrap objects in your array one by one (instead casting it directly to [UserResult]) and try to find out what Type there are by comparing to some set of known types as some of answers from this question suggest.
I would start with verifying the data structure with example code below , and only move on with casting to various type afterwards:
Lets assume example data1 is your data:
let dict1 = ["profileUrl":"www.address1.com","username":"chrissmith"]
let data1: NSArray = [dict1]
//printed data1:
// (
// {
// profileUrl = "www.address1.com";
// username = chrissmith;
// }
// )
if data1[0] as? [String:String] != nil {
print("We found out that first object is dictionary of [String:String]!")
}
else if data1[0] as? Dictionary<NSObject, AnyObject> != nil {
print("We found out that first object is dictionary of mixed values!")
} else {
print("We found out that first object has different data structure")
}
Hopefully this answer was at least a little bit helpfull, even though not providing direct easy solution for your problem.

Where to store Decoded JSON array from server and how to access it globally in viewControllers?

Currently im creating application which parses JSON from my server. From server I can receive array with JSON models.
Data from this array must be populated in table View.
My question Is simple: where to store decoded array from server, if I want to access it from many viewControllers in my application?
Here is my JSON model, which coming from server.
import Foundation
struct MyModel: Codable {
var settings: Test?
var provider: [Provider]
}
extension MyModel {
struct setting: Codable {
var name: String
var time: Int
}
}
here is how I am decoding it
import Foundation
enum GetResourcesRequest<ResourceType> {
case success([ResourceType])
case failure
}
struct ResourceRequest<ResourceType> where ResourceType: Codable {
var startURL = "https://myurl/api/"
var resourceURL: URL
init(resourcePath: String) {
guard let resourceURL = URL(string: startURL) else {
fatalError()
}
self.resourceURL = resourceURL.appendingPathComponent(resourcePath)
}
func fetchData(completion: #escaping
(GetResourcesRequest<ResourceType>) -> Void ) {
URLSession.shared.dataTask(with: resourceURL) { data, _ , _ in
guard let data = data else { completion(.failure)
return }
let decoder = JSONDecoder()
if let jsonData = try? decoder.decode([ResourceType].self, from: data) {
completion(.success(jsonData))
} else {
completion(.failure)
}
}.resume()
}
}
This is an example of CategoriesProvider. It just stores categories in-memory and you can use them across the app. It is not the best way to do it and not the best architecture, but it is simple to get started.
class CategoriesProvider {
static let shared = CategoriesProvider()
private(set) var categories: [Category]?
private let categoryRequest = ResourceRequest<Category>(resourcePath: "categories")
private let dataTask: URLSessionDataTask?
private init() {}
func fetchData(completion: #escaping (([Category]?) -> Void)) {
guard categories == nil else {
completion(categories)
return
}
dataTask?.cancel()
dataTask = categoryRequest.fetchData { [weak self] categoryResult in
var fetchedCategories: [Category]?
switch categoryResult {
case .failure:
print("error")
case .success(let categories):
fetchedCategories = categories
}
DispatchQueue.main.async {
self?.categories = fetchedCategories
completion(fetchedCategories)
}
}
}
}
I suggest using URLSessionDataTask in order to cancel a previous task. It could happen when you call fetchData several times one after another. You have to modify your ResourceRequest and return value of URLSession.shared.dataTask(...)
Here more details about data task https://www.raywenderlich.com/3244963-urlsession-tutorial-getting-started#toc-anchor-004 (DataTask and DownloadTask)
Now you can fetch categories in CategoriesViewController in this way:
private func loadTableViewData() {
CategoriesProvider.shared.fetchData { [weak self] categories in
guard let self = self, let categories = categories else { return }
self.categories = categories
self.tableView.reloadData()
}
}
In the other view controllers, you can do the same but can check for the 'categories' before making a fetch.
if let categories = CategoriesProvider.shared.categories {
// do something
} else {
CategoriesProvider.shared.fetchData { [weak self] categories in
// do something
}
}
If you really want to avoid duplicate load data() calls, your simplest option would be to cache the data on disk (CoreData, Realm, File, etc.) after parsing it the first time.
Then every ViewController that needs the data, can just query your storage system.
Of course the downside of this approach is the extra code you'll have to write to manage the coherency of your data to make sure it's properly managed across your app.
make a global dictionary array outside any class to access it on every viewcontroller.

Rx Observable that gets value from other Observable

I am new to RxSwift and MVVM.
my viewModel has a method named rx_fetchItems(for:) that does the heavy lifting of fetching relevant content from backend, and returns Observable<[Item]>.
My goal is to supply an observable property of the viewModel named collectionItems, with the last emitted element returned from rx_fetchItems(for:), to supply my collectionView with data.
Daniel T has provided this solution that I could potentially use:
protocol ServerAPI {
func rx_fetchItems(for category: ItemCategory) -> Observable<[Item]>
}
struct ViewModel {
let collectionItems: Observable<[Item]>
let error: Observable<Error>
init(controlValue: Observable<Int>, api: ServerAPI) {
let serverItems = controlValue
.map { ItemCategory(rawValue: $0) }
.filter { $0 != nil }.map { $0! } // or use a `filterNil` operator if you already have one implemented.
.flatMap { api.rx_fetchItems(for: $0)
.materialize()
}
.filter { $0.isCompleted == false }
.shareReplayLatestWhileConnected()
collectionItems = serverItems.filter { $0.element != nil }.dematerialize()
error = serverItems.filter { $0.error != nil }.map { $0.error! }
}
}
The only problem here is that my current ServerAPI aka FirebaseAPI, has no such protocol method, because it is designed with a single method that fires all requests like this:
class FirebaseAPI {
private let session: URLSession
init() {
self.session = URLSession.shared
}
/// Responsible for Making actual API requests & Handling response
/// Returns an observable object that conforms to JSONable protocol.
/// Entities that confrom to JSONable just means they can be initialized with json.
func rx_fireRequest<Entity: JSONable>(_ endpoint: FirebaseEndpoint, ofType _: Entity.Type ) -> Observable<[Entity]> {
return Observable.create { [weak self] observer in
self?.session.dataTask(with: endpoint.request, completionHandler: { (data, response, error) in
/// Parse response from request.
let parsedResponse = Parser(data: data, response: response, error: error)
.parse()
switch parsedResponse {
case .error(let error):
observer.onError(error)
return
case .success(let data):
var entities = [Entity]()
switch endpoint.method {
/// Flatten JSON strucuture to retrieve a list of entities.
/// Denoted by 'GETALL' method.
case .GETALL:
/// Key (underscored) is unique identifier for each entity, which is not needed here.
/// value is k/v pairs of entity attributes.
for (_, value) in data {
if let value = value as? [String: AnyObject], let entity = Entity(json: value) {
entities.append(entity)
}
}
// Need to force downcast for generic type inference.
observer.onNext(entities as! [Entity])
observer.onCompleted()
/// All other methods return JSON that can be used to initialize JSONable entities
default:
if let entity = Entity(json: data) {
observer.onNext([entity] as! [Entity])
observer.onCompleted()
} else {
observer.onError(NetworkError.initializationFailure)
}
}
}
}).resume()
return Disposables.create()
}
}
}
The most important thing about the rx_fireRequest method is that it takes in a FirebaseEndpoint.
/// Conforms to Endpoint protocol in extension, so one of these enum members will be the input for FirebaseAPI's `fireRequest` method.
enum FirebaseEndpoint {
case saveUser(data: [String: AnyObject])
case fetchUser(id: String)
case removeUser(id: String)
case saveItem(data: [String: AnyObject])
case fetchItem(id: String)
case fetchItems
case removeItem(id: String)
case saveMessage(data: [String: AnyObject])
case fetchMessages(chatroomId: String)
case removeMessage(id: String)
}
In order to use Daniel T's solution, Id have to convert each enum case from FirebaseEndpoint into methods inside FirebaseAPI. And within each method, call rx_fireRequest... If I'm correct.
Id be eager to make this change if it makes for a better Server API design. So the simple question is, Will this refactor improve my overall API design and how it interacts with ViewModels. And I realize this is now evolving into a code review.
ALSO... Here is implementation of that protocol method, and its helper:
func rx_fetchItems(for category: ItemCategory) -> Observable<[Item]> {
// fetched items returns all items in database as Observable<[Item]>
let fetchedItems = client.rx_fireRequest(.fetchItems, ofType: Item.self)
switch category {
case .Local:
let localItems = fetchedItems
.flatMapLatest { [weak self] (itemList) -> Observable<[Item]> in
return self!.rx_localItems(items: itemList)
}
return localItems
// TODO: Handle other cases like RecentlyAdded, Trending, etc..
}
}
// Helper method to filter items for only local items nearby user.
private func rx_localItems(items: [Item]) -> Observable<[Item]> {
return Observable.create { observable in
observable.onNext(items.filter { $0.location == "LA" })
observable.onCompleted()
return Disposables.create()
}
}
If my approach to MVVM or RxSwift or API design is wrong PLEASE do critique.
I know it is tough to start understanding RxSwift
I like to use Subjects or Variables as inputs for the ViewModel and Observables or Drivers as outputs for the ViewModel
This way you can bind the actions that happen on the ViewController to the ViewModel, handle the logic there, and update the outputs
Here is an example by refactoring your code
View Model
// Inputs
let didSelectItemCategory: PublishSubject<ItemCategory> = .init()
// Outputs
let items: Observable<[Item]>
init() {
let client = FirebaseAPI()
let fetchedItems = client.rx_fireRequest(.fetchItems, ofType: Item.self)
self.items = didSelectItemCategory
.withLatestFrom(fetchedItems, resultSelector: { itemCategory, fetchedItems in
switch itemCategory {
case .Local:
return fetchedItems.filter { $0.location == "Los Angeles" }
default: return []
}
})
}
ViewController
segmentedControl.rx.value
.map(ItemCategory.init(rawValue:))
.startWith(.Local)
.bind(to: viewModel.didSelectItemCategory)
.disposed(by: disposeBag)
viewModel.items
.subscribe(onNext: { items in
// Do something
})
.disposed(by: disposeBag)
I think the problem you are having is that you are only going half-way with the observable paradigm and that's throwing you off. Try taking it all the way and see if that helps. For example:
protocol ServerAPI {
func rx_fetchItems(for category: ItemCategory) -> Observable<[Item]>
}
struct ViewModel {
let collectionItems: Observable<[Item]>
let error: Observable<Error>
init(controlValue: Observable<Int>, api: ServerAPI) {
let serverItems = controlValue
.map { ItemCategory(rawValue: $0) }
.filter { $0 != nil }.map { $0! } // or use a `filterNil` operator if you already have one implemented.
.flatMap { api.rx_fetchItems(for: $0)
.materialize()
}
.filter { $0.isCompleted == false }
.shareReplayLatestWhileConnected()
collectionItems = serverItems.filter { $0.element != nil }.dematerialize()
error = serverItems.filter { $0.error != nil }.map { $0.error! }
}
}
EDIT to handle problem mentioned in comment. You now need to pass in the object that has the rx_fetchItems(for:) method. You should have more than one such object: one that points to the server and one that doesn't point to any server, but instead returns canned data so you can test for any possible response, including errors. (The view model should not talk to the server directly, but should do so through an intermediary...
The secret sauce in the above is the materialize operator that wraps error events into a normal event that contains an error object. That way you stop a network error from shutting down the whole system.
In response to the changes in your question... You can simply make the FirebaseAPI conform to ServerAPI:
extension FirebaseAPI: ServerAPI {
func rx_fetchItems(for category: ItemCategory) -> Observable<[Item]> {
// fetched items returns all items in database as Observable<[Item]>
let fetchedItems = self.rx_fireRequest(.fetchItems, ofType: Item.self)
switch category {
case .Local:
let localItems = fetchedItems
.flatMapLatest { [weak self] (itemList) -> Observable<[Item]> in
return self!.rx_localItems(items: itemList)
}
return localItems
// TODO: Handle other cases like RecentlyAdded, Trending, etc..
}
}
// Helper method to filter items for only local items nearby user.
private func rx_localItems(items: [Item]) -> Observable<[Item]> {
return Observable.create { observable in
observable.onNext(items.filter { $0.location == "LA" })
observable.onCompleted()
return Disposables.create()
}
}
}
You should probably change the name of ServerAPI at this point to something like FetchItemsAPI.
You run into a tricky situation here because your observable can throw an error and once it does throw an error the observable sequence errors out and no more events can be emitted. So to handle subsequent network requests, you must reassign taking the approach you're currently taking. However, this is generally not good for driving UI elements such as a collection view because you would have to bind to the reassigned observable every time. When driving UI elements, you should lean towards types that are guaranteed to not error out (i.e. Variable and Driver). You could make your Observable<[Item]> to be let items = Variable<[Item]>([]) and then you could just set the value on that variable to be the array of items that came in from the new network request. You can safely bind this variable to your collection view using RxDataSources or something like that. Then you could make a separate variable for the error message, let's say let errorMessage = Variable<String?>(nil), for the error message that comes from the network request and then you could bind the errorMessage string to a label or something like that to display your error message.

How to get a swift enum's associated value regardless of the enum case

I have an object FormField which has two properties: a String name, and a value which can accept any type--hence I've made it Any!. However, I've been told in a separate question to use an enum with associated values instead of Any!.
enum Value {
case Text(String!)
case CoreDataObject(NSManagedObject!)
}
class FormField {
var name: String
var value: Value?
// initializers...
}
This approach makes it awfully verbose to check for nullity however. If I wanted to display an alert view for all the missing fields in the form, I'll have to repeat a nil check for every case in a switch statement:
for field in self.fields {
if let value = field.value {
switch value {
case .Text(let text):
if text == nil {
missingFields.append(field.name)
}
case .CoreDataObject(let object):
if object == nil {
missingFields.append(field.name)
}
}
}
}
Is there a shorter way of accessing the enum's associated value, regardless of the type? If I make FormField.value an Any! the above code would be as easy as:
for field in self.fields {
if field.value == nil {
missingFields.append(field.name)
}
}
Define a method isMissing() inside the enum - write it once and only once. Then you get nearly exactly what you prefer:
for field in self.fields {
if field.value.isMissing() {
missingFields.append(field.name)
}
}
It would look something like this (from the Swift Interpreter):
1> class Foo {}
>
2> enum Value {
3. case One(Foo!)
4. case Two(Foo!)
5.
6. func isMissing () -> Bool {
7. switch self {
8. case let .One(foo): return foo == nil
9. case let .Two(foo): return foo == nil
10. }
11. }
12. }
13> let aVal = Value.One(nil)
aVal: Value = One {
One = nil
}
14> aVal.isMissing()
$R0: Bool = true
With Swift 2 it's possible to get the associated value using reflection.
To make that easier just add the code below to your project and extend your enum with the EVAssociated protocol.
public protocol EVAssociated {
}
public extension EVAssociated {
public var associated: (label:String, value: Any?) {
get {
let mirror = Mirror(reflecting: self)
if let associated = mirror.children.first {
return (associated.label!, associated.value)
}
print("WARNING: Enum option of \(self) does not have an associated value")
return ("\(self)", nil)
}
}
}
Then you can access the .asociated value with code like this:
class EVReflectionTests: XCTestCase {
func testEnumAssociatedValues() {
let parameters:[EVAssociated] = [usersParameters.number(19),
usersParameters.authors_only(false)]
let y = WordPressRequestConvertible.MeLikes("XX", Dictionary(associated: parameters))
// Now just extract the label and associated values from this enum
let label = y.associated.label
let (token, param) = y.associated.value as! (String, [String:Any]?)
XCTAssertEqual("MeLikes", label, "The label of the enum should be MeLikes")
XCTAssertEqual("XX", token, "The token associated value of the enum should be XX")
XCTAssertEqual(19, param?["number"] as? Int, "The number param associated value of the enum should be 19")
XCTAssertEqual(false, param?["authors_only"] as? Bool, "The authors_only param associated value of the enum should be false")
print("\(label) = {token = \(token), params = \(param)")
}
}
// See http://github.com/evermeer/EVWordPressAPI for a full functional usage of associated values
enum WordPressRequestConvertible: EVAssociated {
case Users(String, Dictionary<String, Any>?)
case Suggest(String, Dictionary<String, Any>?)
case Me(String, Dictionary<String, Any>?)
case MeLikes(String, Dictionary<String, Any>?)
case Shortcodes(String, Dictionary<String, Any>?)
}
public enum usersParameters: EVAssociated {
case context(String)
case http_envelope(Bool)
case pretty(Bool)
case meta(String)
case fields(String)
case callback(String)
case number(Int)
case offset(Int)
case order(String)
case order_by(String)
case authors_only(Bool)
case type(String)
}
The code above is now available as a cocoapod susbspec at
https://github.com/evermeer/Stuff#enum
It also has an other nice enum extension for enumerating all enum values.
If the associated values were of the same type for all enum cases the following approach could help.
enum Value {
case text(NSString!), two(NSString!), three(NSString!) // This could be any other type including AnyClass
}
// Emulating "fields" datastruct for demo purposes (as if we had struct with properties).
typealias Field = (en: Value, fieldName: String)
let fields: [Field] = [(.text(nil),"f1"), (.two(nil), "f2"), (.three("Hey"), "f3")] // this is analog of "fields"
let arrayOfFieldNamesWithEmptyEnums: [String] = fields.compactMap({
switch $0.en {
case let .text(foo), let .two(foo), let .three(foo): if foo == nil { return $0.fieldName } else { return nil }}
})
print("arrayOfFieldNamesWithEmptyEnums \(arrayOfFieldNamesWithEmptyEnums)")
Many other things can be obtained similarly.
let arrayOfEnumsWithoutValues: [Value] = fields.compactMap({
switch $0.en {
case let .text(foo), let .two(foo), let .three(foo): if foo == nil { return $0.en } else { return nil }}
})
print("arrayOfEnumsWithoutValues \(arrayOfEnumsWithoutValues)")
// just to check ourselves
if let index = arrayOfEnumsWithoutValues.index(where: { if case .two = $0 { return true }; return false }) {
print(".two found at index \(index)")
}

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