Promises simplify asynchronous programming, freeing you up to focus on the more important things

by iOS Example

Promises simplify asynchronous programming, freeing you up to focus on the more
important things. They are easy to learn, easy to master and result in clearer,
more readable code. Your co-workers will thank you.

UIApplication.shared.isNetworkActivityIndicatorVisible = true

let fetchImage = URLSession.shared.dataTask(.promise, with: url).compactMap{ UIImage(data: $0.data) }
let fetchLocation = CLLocationManager.requestLocation().lastValue

firstly {
    when(fulfilled: fetchImage, fetchLocation)
}.done { image, location in
    self.imageView.image = image
    self.label.text = "\(location)"
}.ensure {
    UIApplication.shared.isNetworkActivityIndicatorVisible = false
}.catch { error in
    self.show(UIAlertController(for: error), sender: self)
}

PromiseKit is a thoughtful and complete implementation of promises for any
platform that has a swiftc. It has excellent Objective-C bridging and
delightful specializations for iOS, macOS, tvOS and watchOS. It is a top-100
pod used in many of the most popular apps in the world.

PromiseKit 6

Release notes and migration guide.

Quick Start

In your Podfile:

use_frameworks!

target "Change Me!" do
  pod "PromiseKit", "~> 6.8"
end

The above gives an Xcode warning? See our Installation Guide.

PromiseKit 6, 5 and 4 support Xcode 8.3, 9.x and 10.0; Swift 3.1,
3.2, 3.3, 3.4, 4.0, 4.1, 4.2, 4.3 and 5.0 (development snapshots); iOS, macOS,
tvOS, watchOS, Linux and Android; CocoaPods, Carthage and SwiftPM;
(CI Matrix).

For Carthage, SwiftPM, Accio, etc., or for instructions when using older Swifts or Xcodes, see our Installation Guide. We recommend
Carthage or
Accio.

Professionally Supported PromiseKit is Now Available

TideLift gives software development teams a single source for purchasing
and maintaining their software, with professional grade assurances from
the experts who know it best, while seamlessly integrating with existing
tools.

Get Professional Support for PromiseKit with TideLift.

PromiseKit is Thousands of Hours of Work

Hey there, I’m Max Howell. I’m a prolific producer of open source software and
probably you already use some of it (I created brew). I work full-time on
open source and it’s hard; currently I earn less than minimum wage. Please
help me continue my work, I appreciate it ??

Other ways to say thanks.

Documentation

Extensions

Promises are only as useful as the asynchronous tasks they represent. Thus, we
have converted (almost) all of Apple’s APIs to promises. The default CocoaPod
provides Promises and the extensions for Foundation and UIKit. The other
extensions are available by specifying additional subspecs in your Podfile,
e.g.:

pod "PromiseKit/MapKit"          # MKDirections().calculate().then { /*…*/ }
pod "PromiseKit/CoreLocation"    # CLLocationManager.requestLocation().then { /*…*/ }

All our extensions are separate repositories at the PromiseKit organization.

I don't want the extensions!

Then don’t have them:

pod "PromiseKit/CorePromise", "~> 6.8"

Note: Carthage installations come with no extensions by default.

Choose Your Networking Library

Promise chains commonly start with a network operation. Thus, we offer
extensions for URLSession:

// pod 'PromiseKit/Foundation'  # https://github.com/PromiseKit/Foundation

firstly {
    URLSession.shared.dataTask(.promise, with: try makeUrlRequest()).validate()
    // ^^ we provide `.validate()` so that eg. 404s get converted to errors
}.map {
    try JSONDecoder().decode(Foo.self, with: $0.data)
}.done { foo in
    //…
}.catch { error in
    //…
}

func makeUrlRequest() throws -> URLRequest {
    var rq = URLRequest(url: url)
    rq.httpMethod = "POST"
    rq.addValue("application/json", forHTTPHeaderField: "Content-Type")
    rq.addValue("application/json", forHTTPHeaderField: "Accept")
    rq.httpBody = try JSONEncoder().encode(obj)
    return rq
}

And Alamofire:

// pod 'PromiseKit/Alamofire'  # https://github.com/PromiseKit/Alamofire-

firstly {
    Alamofire
        .request("http://example.com", method: .post, parameters: params)
        .responseDecodable(Foo.self)
}.done { foo in
    //…
}.catch { error in
    //…
}

Nowadays, considering that:

  • We almost always POST JSON
  • We now have JSONDecoder
  • PromiseKit now has map and other functional primitives
  • PromiseKit (like Alamofire, but not raw-URLSession) also defaults to having
    callbacks go to the main thread

We recommend vanilla URLSession. It uses fewer black boxes and sticks closer to the metal. Alamofire was essential until the three bullet points above
became true, but nowadays it isn’t really necessary.

Support

Please check our Troubleshooting Guide, and
if after that you still have a question, ask at our Gitter chat channel or on our bug tracker.

Security & Vulnerability Reporting or Disclosure

https://tidelift.com/security

GitHub

https://github.com/mxcl/PromiseKit