SwiftUI/Combine - Subscribing to the latest value of a single Publisher - swift

Question

I'm playing around a tad with Combine and SwiftUI for a little pet project of mine, learning as I go.
Here's the LoginModel at it current state:
public class LoginModel: ObservableObject {
#Published var domain: String = ""
#Published var email: String = ""
#Published var password: String = ""
#Published var isValid: Bool = false
public var didChange = PassthroughSubject<Void, Never>()
var credentialsValidPublisher: AnyPublisher<Bool, Never> {
Publishers.CombineLatest($email, $password)
.receive(on: RunLoop.main)
.map { (email, password) in
let emailValid = String.emailValid(emailString: email) // String extension function
let passwordValid = password.count > 5
return emailValid && passwordValid
}
.breakpointOnError()
.eraseToAnyPublisher()
}
init() {
// This works just fine
_ = credentialsValidPublisher.sink { isValid in
self.isValid = isValid
}
// However this does not work at all
_ = domain
.publisher
.receive(on: RunLoop.main)
.sink { value in
print(value)
}
}
}
Now from my current understanding is that a #Published var foo: String already has a Publisher attached to it. And that one should be able to use this directly to subscribe to its changes.
Changing credentialsValidPublisher variable over to this works too:
var credentialsValidPublisher: AnyPublisher<Bool, Never> {
Publishers.CombineLatest3($domain, $email, $password)
.receive(on: RunLoop.main)
.map { (domain, email, password) in
let domainValid = URL.isValidURL(urlString: domain)
let emailValid = String.emailValid(emailString: email)
let passwordValid = password.count > 5
return domainValid && emailValid && passwordValid
}
.breakpointOnError()
.eraseToAnyPublisher()
}
But this is not what I want. In my case I need a special Publisher in order to map a valid URL string over to a network request and then ping the server at hand to see if the provided server is responding.
Also this model is then connected to a SwiftUI view with a bunch of SwiftUI TextFields.
Any help to point me in the right direction will be highly appreciated.

Answer 1

So I figure out the way to do it.
In the LoginModel underneath var credentialsValidPublisher: AnyPublisher<Bool, Never> I added:
var domainValidPublisher: AnyPublisher<Bool, Never> {
$domain
.debounce(for: 0.5, scheduler: DispatchQueue.main)
.removeDuplicates()
.map { domain in
URL.isValidURL(urlString: domain)
}
.eraseToAnyPublisher()
}
Then I can just subscribe to it in init.
I also added AnyCancellable properties that we call .cancel() on deinit.
Here's what the updated model looks like:
public class LoginModel: ObservableObject {
#Published var domain: String = ""
#Published var email: String = ""
#Published var password: String = ""
#Published var isValid: Bool = false
public var didChange = PassthroughSubject<Void, Never>()
private var credentialsValidPublisherCancellable: AnyCancellable!
private var domainValidCancellable: AnyCancellable!
var credentialsValidPublisher: AnyPublisher<Bool, Never> {
Publishers.CombineLatest3($domain, $email, $password)
.receive(on: RunLoop.main)
.map { (domain, email, password) in
let domainValid = URL.isValidURL(urlString: domain)
let emailValid = String.emailValid(emailString: email)
let passwordValid = password.count > 5
return domainValid && emailValid && passwordValid
}
.breakpointOnError()
.eraseToAnyPublisher()
}
var domainValidPublisher: AnyPublisher<Bool, Never> {
$domain
.debounce(for: 0.5, scheduler: DispatchQueue.main)
.removeDuplicates()
.map { domain in
URL.isValidURL(urlString: domain)
}
.eraseToAnyPublisher()
}
init() {
credentialsValidPublisherCancellable = credentialsValidPublisher.sink { isValid in
self.isValid = isValid
}
domainValidCancellable = domainValidPublisher.sink { isValid in
print("isValid: \(isValid)")
}
}
deinit {
credentialsValidPublisherCancellable.cancel()
domainValidCancellable.cancel()
}
}