[英]RxSwift Variable composition without subscribe/bind/drive
I need some internal state in a viewModel but also trying to follow the "no subscription / bind / drive / ..." ideal approach and only compose between Observables
. 我需要在viewModel中有一些内部状态,但也要尝试遵循“无订阅/绑定/驱动器/ ...”的理想方法,并且只能在
Observables
之间进行Observables
。
How can I specify what a Variable
observes? 如何指定
Variable
观测值?
Example: 例:
private var userProfilesToFetch = Variable<[String]>([])
private var users: Variable<[User]> {
return //something that observes fetchUserProfiles() and when it emits, appends to its .value
}
private func fetchUserProfiles() -> Observable<User?> {
let reference = databaseRef.child("users")
return userProfilesToFetch.asObservable()
.filter({ $0 != [] })
.map({ $0.last! })
.flatMap({ (userId) -> Observable<User?> in
return self.service.observeAllChildren(of: reference.child(userId), by: .value)
.map({ (snapshot) -> User? in
guard let values = snapshot.value as? [String: AnyObject] else { return nil }
var user = User(dictionary: values)
user.id = snapshot.key
return user
})
})
}
The "ideal approach" is to avoid the use of Subjects/Variables. “理想方法”是避免使用主题/变量。 Instead, favor sequence emitters (functions that return an observable,) sequence receivers (functions that accept an observable as a parameter,) and sequence transformers (functions that do both.)
取而代之的是,偏爱序列发射器(返回可观察到的函数),序列接收器(接受可观察到的函数作为参数)和序列转换器(两者都执行的函数)。
Sequence emitters and receivers necessarily perform side effects and inside a sequence receiver, there is necessarily a subscribe/bind in order to unpack the value and use it. 序列发射器和接收器必然会产生副作用,并且在序列接收器内部 ,必须有一个订阅/绑定才能拆开值并使用它。
There should be a direct and obvious link between the emitters and receivers. 发射器和接收器之间应该有直接明显的联系。 Subjects/Variables tend to break that link.
主题/变量倾向于破坏该链接。
In this ideal approach, your "view model" is not a class/struct containing a bunch of variables. 在这种理想的方法中,您的“视图模型”不是包含一堆变量的类/结构。 Your view model is a function that takes observables as parameters and returns observables for the view controller to bind to.
您的视图模型是一个函数,将可观察值作为参数并返回可观察值以供视图控制器绑定。 For example:
例如:
class MyViewController: UIViewController {
@IBOutlet weak var name: UITextView!
@IBOutlet weak var label: UILabel!
override
func viewDidLoad() {
super.viewDidLoad()
let viewModel = myViewModel(name: name.rx.text.orEmpty)
viewModel.label.bind(to: label.rx.text).disposed(by: bag)
}
let bag = DisposeBag()
}
struct MyViewModel {
let label: Observable<String>
}
// this function could be turned into an `init` method on the MyViewModel struct if you would prefer.
fun myViewModel(name: Observable<String>) -> MyViewModel {
let label = name.map { "Hello \($0)!" }
return MyViewModel(label: label)
}
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