Passed in data MVVM RxSwift - ios

Question

I want to learn MVVM RxSwift with input and output method, I want to get a username from textfield.
I have a scenario when user not enter a username it will present an error and when user enter a username it will present in viewController.
This is when I confuse. I got the error message and successfully present error but, how can I catch the query in my viewModel and passed the data to viewController.
This is how I setup my searchViewModel
protocol ViewModelType {
associatedtype Input
associatedtype Output
func transform(input: Input) -> Output
}
class SearchViewModel: ViewModelType {
// MARK: Binding
struct Input {
let searchText: Observable<String>
let validate: Observable<Void>
}
struct Output {
let username: Driver<String>
}
func transform(input: Input) -> Output {
let username = input.validate
.withLatestFrom(input.searchText)
.map { query in
if query.isEmpty {
return "Please enter a username. We need to know who to look for"
} else {
return query
}
}.asDriver(onErrorJustReturn: "")
return Output(username: username)
}
}
and this is my viewDidLoad in SearchViewController
let searchTextField = GFTextField()
let calloutBtn = GFButton(backgroundColor: .systemGreen, title: "Get followers")
private let disposeBag = DisposeBag()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .systemBackground
setupImageView()
setupTextfield()
setupCalloutBtn()
let input = SearchViewModel.Input(
searchText: searchTextField.rx.text.orEmpty.asObservable(),
validate: calloutBtn.rx.tap.asObservable())
let output = viewModel.transform(input: input)
output.username.drive { [weak self] username in
guard let self = self else { return }
self.presentGFAlertOnMainThread(title: "Empty Username", message: username, buttonTitle: "Dismiss")
}.disposed(by: disposeBag)
}

Answer 1

It depends on what you want to do with the text of course, but below I assume you want to make a network request. But of course that requires understanding what your API layer looks like. I have to make some assumptions there as well, but the key is that you need to inject your API layer into your view model through its constructor/init method.
Like this:
class SearchViewModel: ViewModelType {
struct Input {
let username: Observable<String>
let getFollowers: Observable<Void>
}
struct Output {
let errorMessage: Driver<String>
let followers: Driver<[Follower]>
}
let api: API
init(api: API) {
self.api = api
}
func transform(input: Input) -> Output {
let followersResponse = input.getFollowers
.withLatestFrom(input.username)
.filter { !$0.isEmpty }
.map { makeEndpoint(using: $0) }
.flatMap { [api] in
api.load($0)
}
.share()
let missingName = input.getFollowers
.withLatestFrom(input.username)
.compactMap { $0.isEmpty ? "Please enter a username. We need to know who to look for" : nil }
let errorMessage = Observable.merge(
api.error.map { $0.localizedDescription },
missingName
)
.asDriver(onErrorJustReturn: "")
let followers = followersResponse
.asDriver(onErrorJustReturn: [])
return Output(errorMessage: errorMessage, followers: followers)
}
}
-- EDIT --
If all you want to do is push the non-empty text field back to the view controller, then it would look like this:
class SearchViewModel: ViewModelType {
struct Input {
let username: Observable<String>
let getFollowers: Observable<Void>
}
struct Output {
let errorMessage: Driver<String>
let username: Driver<String>
}
func transform(input: Input) -> Output {
let errorMessage = input.getFollowers
.withLatestFrom(input.username)
.compactMap { $0.isEmpty ? "Please enter a username. We need to know who to look for" : nil }
.asDriver(onErrorJustReturn: "")
let username = input.getFollowers
.withLatestFrom(input.username)
.filter { !$0.isEmpty }
.asDriver(onErrorJustReturn: "")
return Output(errorMessage: errorMessage, username: username)
}
}
The key here is that you need a Driver for each output that the view controller will want to subscribe to.