IndefiniteObservable 4.0.0

IndefiniteObservable 4.0.0

TestsTested
LangLanguage SwiftSwift
License Apache 2
ReleasedLast Release Apr 2017
SwiftSwift Version 3.0
SPMSupports SPM

Maintained by Jeff Verkoeyen.


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  • By
  • The Material Motion Authors

IndefiniteObservable.swift

IndefiniteObservable is a minimal implementation of Observable with no concept of completion or failure.

Supported languages

  • Swift 3

This library does not support Objective-C due to its heavy use of generics.

Installation

Usage

Import the framework:

@import IndefiniteObservable;

You will now have access to all of the APIs.

Example apps/unit tests

Check out a local copy of the repo to access the Catalog application by running the following commands:

git clone https://github.com/material-motion/indefinite-observable-swift.git
cd observable-swift
pod install
open IndefiniteObservable.xcworkspace

Guides

  1. How to make an observable
  2. How to create a synchronous stream
  3. How to create an asynchronous stream using blocks
  4. How to subscribe to a stream
  5. How to unsubscribe from a stream
  6. How to create an synchronous stream using objects

How to make an observable

In this example we’ll make the simplest possible observable type: a value observable. We will use this concrete type in all of the following guides.

final class ValueObserver<T>: Observer {
  typealias Value = T

  init(_ next: @escaping (T) -> Void) {
    self.next = next
  }

  let next: (T) -> Void
}

final class ValueObservable<T>: IndefiniteObservable<ValueObserver<T>> {
  func subscribe(_ next: @escaping (T) -> Void) -> Subscription {
    return super.subscribe(observer: ValueObserver(next))
  }
}

How to create a synchronous stream

let observable = ValueObservable<<#ValueType#>> { observer in
  observer.next(<#value#>)
  return noopDisconnect
}

How to create an asynchronous stream using blocks

If you have an API that provides a block-based mechanism for registering observers then you can create an asynchronous stream in place like so:

let observable = ValueObservable<<#ValueType#>> { observer in
  let someToken = registerSomeCallback { callbackValue in
    observer.next(callbackValue)
  }

  return {
    unregisterCallback(someToken)
  }
}

How to subscribe to a stream

observable.subscribe { value in
  print(value)
}

How to unsubscribe from a stream

Unsubscribing will invoke the observable’s disconnect method. To unsubscribe, you must retain a reference to the subscription instance returned by subscribe.

let subscription = observable.subscribe { value in
  print(value)
}

subscription.unsubscribe()

How to create an synchronous stream using objects

Many iOS/macOS APIs use delegation for event handling. To connect delegates with a stream you will need to create a Producer class. A Producer listens for events with an event delegate like didTap and forwards those events to an IndefiniteObservable’s observer.

Final result

class DragConnection {
  typealias Value = (state: UIGestureRecognizerState, location: CGPoint)

  init(subscribedTo gesture: UIPanGestureRecognizer, observer: ValueObserver<Value>) {
    self.gesture = gesture
    self.observer = observer

    gesture.addTarget(self, action: #selector(didPan))

    // Populate the observer with the current gesture state.
    observer.next(currentValue(for: gesture))
  }

  @objc func didPan(_ gesture: UIPanGestureRecognizer) {
    observer.next(currentValue(for: gesture))
  }

  func currentValue(for gesture: UIPanGestureRecognizer) -> Value {
    return (gesture.state, gesture.location(in: gesture.view!))
  }

  func disconnect() {
    gesture?.removeTarget(self, action: #selector(didPan))
    gesture = nil
  }

  var gesture: (UIPanGestureRecognizer)?
  let observer: ValueObserver<Value>
}

let pan = UIPanGestureRecognizer()
view.addGestureRecognizer(pan)

let dragStream = ValueObservable<DragConnection.Value> { observer in
  return DragConnection(subscribedTo: pan, observer: observer).disconnect
}
let subscription = dragStream.subscribe {
  dump($0.state)
  dump($0.location)
}

Step 1: Define the Producer type

A Producer should be a type of Subscription.

class <#Name#>Producer: Subscription {
}

Step 2: Define the Value type

class DragConnection: Subscription {
  typealias Value = (state: UIGestureRecognizerState, location: CGPoint)
}

Step 3: Implement the initializer

Your initializer must accept and store an ValueObserver<Value> instance.

  init(subscribedTo gesture: UIPanGestureRecognizer, observer: ValueObserver<Value>) {
    self.gesture = gesture
    self.observer = observer
  }

  var gesture: (UIPanGestureRecognizer)?
  let observer: ValueObserver<Value>

Step 4: Connect to the event source and send values to the observer

  init(subscribedTo gesture: UIPanGestureRecognizer, observer: ValueObserver<Value>) {
    ...

    gesture.addTarget(self, action: #selector(didPan))
  }

  @objc func didPan(_ gesture: UIPanGestureRecognizer) {
    observer.next(currentValue(for: gesture))
  }

  func currentValue(for gesture: UIPanGestureRecognizer) -> Value {
    return (gesture.state, gesture.location(in: gesture.view!))
  }

Step 5: Implement disconnect

You are responsible for disconnecting from and releasing any resources here.

  func disconnect() {
    gesture?.removeTarget(self, action: #selector(didPan))
    gesture = nil
  }

Step 6: (Optional) Provide the initial state

It often is helpful to provide the observer with the current state on registration.

  init(subscribedTo gesture: UIPanGestureRecognizer, observer: ValueObserver<Value>) {
    ...

    // Populate the observer with the current gesture state.
    observer.next(currentValue(for: gesture))
  }

Step 7: Observe the producer

let dragStream = ValueObservable<DragConnection.Value> { observer in
  return DragConnection(subscribedTo: pan, observer: observer).disconnect
}
let subscription = dragStream.subscribe {
  dump($0)
}

Contributing

This library is meant to be a minimal implementation that never grows. As such, we only encourage contributions in the form of documentation, tests, and examples.

Learn more about our team, our community, and our contributor essentials.

License

Licensed under the Apache 2.0 license. See LICENSE for details.