handle nested observables in RxSwift - ios

Question

I'm trying to combine facebook login with a rest call, so when the user is logged in it should make an authenticate call to the server, where the server makes the graph calls, however I'm a bit confused to how I nest the calls with RxSwift? so far I have a FacebookProvider class with following method
func login() -> Observable<String> {
return Observable.create({ observer in
let loginManager = LoginManager()
//LogOut before
loginManager.logOut()
//Set Login Method
loginManager.loginBehavior = .native
//Login Closure
loginManager.logIn([ .publicProfile, .userFriends, .email], viewController: self.parentController) { loginResult in
switch loginResult {
case .failed(let error):
print(error)
observer.onError(FacebookError.NoConnection(L10n.networkError))
case .cancelled:
print("User cancelled login.")
case .success(_, let declinedPermissions, let accessToken):
print("Logged in!")
guard declinedPermissions.count > 0 else {
observer.onError(FacebookError.DeclinedPermission(L10n.declinedPermission))
return
}
observer.onNext(accessToken.authenticationToken)
observer.onCompleted()
}
}
return Disposables.create()
})
}
Then I have a LoginViewModel with this model
public func retrieveUserData() -> Observable<User> {
return Network.provider
.request(.auth(fbToken: Globals.facebookToken)).retry(5).debug().mapObject(User.self)
}
then I in my UIViewController do this
facebookProvider.validate().subscribe({ [weak self] response in
switch response {
case .error(_):
// User is not logged in push to loginController
break
case .next():
//user is logged in retrieveUserData before proceeding
self?.loginViewModel.retrieveUserData().subscribe { event in
switch event {
case .next(let response):
print(response)
case .error(let error):
print(error)
case .completed:
print("completed")
}
}.addDisposableTo(self?.disposeBag)
break
case .completed:
//data is retrieved and can now push to app
break
}
}).addDisposableTo(disposeBag)
Validate
public func rx_validate() -> Observable<String> {
return Observable.create({ observer in
//Check if AccessToken exist
if AccessToken.current == nil {
observer.onError(FacebookError.NotLoggedIn)
} else {
observer.onNext(Globals.accessToken)
}
observer.onCompleted()
return Disposables.create()
})
}

Answer 1

You will want to use flatMap
The closure passed to flatMap will return an observable. flatMap will then take care of un-nesting it, meaning if the closure returns a value of type Observable<T>, and you call flatMap on a value of type Observable<U>, the resulting observable will be Observable<T> (an not Observable<Observable<T>>
In this particular case, the code would look like this:
facebookProvider.validate().flatMap { [weak self] _ in
return self?.loginViewModel.retrieveUserData()
}.subscribe { event in
switch event {
// ...
}
}.addDisposableTo(disposeBag)
On a side note, you should probably update func retrieveUserData() to accept the token as a parameter, instead of fetching it from your Globals structure.
The resulting code would look similar to this
public func retrieveUserData(token: String) -> Observable<User> {
return Network.provider
.request(.auth(fbToken: token)).retry(5).debug().mapObject(User.self)
}
in viewController
facebookProvider.validate().flatMap { [weak self] token in
return self?.loginViewModel.retrieveUserData(token: token)
}.subscribe { event in
switch event {
// ...
}
}.addDisposableTo(disposeBag)