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Observable is the easiest way to observe values in Swift.

How to

Create an Observable and MutableObservable

Using MutableObservable you can create and observe event. Using Observable you can observe event, 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: Observable<CGPoint> = {
        return positionSubject
    }
    // Or use the helper method Observable.asObservable()
    // lazy var position = positionSubject.asObservable()

    /// Private property, that can be changed / observed inside this view model.
    private let positionSubject = MutableObservable(CGPoint.zero)
}

Create Observer with custom onDispose functionality

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()
}

Model Properties as @MutableObservable

Now mark your binded/mapped properties as observable and export public observable

//Private Observer
@MutableObservable var text: String = "Test"

//add observer

_text.observe { (newValue, oldValue) in
    print(newValue)
}.add(to: &disposable)
        
//Public Observer

var textObserve: ImmutableObservable<String> {
    return _text
}

Add an observer

position.observe { p in
    // handle new position
}

Add an observer and specify the DispatchQueue

position.observe(DispatchQueue.main) { p in
// handle new position
}

Change the value

position.wrappedValue = p

Stop observing new values

position.observe {
    // This will stop all observers added to `disposal`
    self.disposal.dispose()
}.add(to: &disposal)

Memory management

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

Installation

CocoaPods

Observable is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Observable'

Swift Package Manager

Observable is available through Swift Package Manager. Swift Package Manager (SwiftPM) is a tool for automating the distribution of Swift code. It is integrated into the swift compiler and from Xcode 11, SwiftPM got natively integrated with Xcode.

dependencies: [
    .package(url: "https://github.com/roberthein/Observable", from: "VERSION")
]

roberthein/Observable

roberthein

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