Observable is the easiest way to observe values in Swift.
var position = Observable(CGPoint.zero)
Using ImmutableObservable
we can create an "readonly"-Observable, in order to avoid side-effects on our internal API.
class SomeViewModel {
/// Public property, that can be read / observed by external classes (e.g. view controller), but not changed.
var position: ImmutableObservable<CGPoint> = {
return positionSubject
}
// Or use the helper method Observable.asImmutable()
// lazy var position = positionSubject.asImmutable()
/// Private property, that can be changed / observed inside this view model.
private let positionSubject = Observable(CGPoint.zero)
}
In some cases Observables require resources while they're active that must be cleaned up when they're disposed of. To handle such cases you can pass an optional block to the Observable initializer to be executed when the Observable is disposed of.
url.startAccessingSecurityScopedResource()
let observable = Observable([URL]()) {
url.stopAccessingSecurityScopedResource()
}
position.observe { p in
// handle new position
}
position.observe(DispatchQueue.main) { p in
// handle new position
}
position.value = p
For a single observer you can store the returned Disposable
to a variable
disposable = position.observe { p in
For multiple observers you can add the disposable to a Disposal
variable
position.observe { }.add(to: &disposal)
And always weakify self
when referencing self
inside your observer
position.observe { [weak self] position in
Observable is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod 'Observable'
Feel free to create a pull request, open an issue or find me on Twitter.