Swen - An Event Bus written in Swift

• Typesafe events
• Pass custom objects
• Threadsafe
• Sticky events
• Fast and small

Installation

Swen is available through CocoaPods, Carthage and Swift Package Manager.

CocoaPods

To install it using CocoaPods, simply add the following line to your Podfile:

pod "Swen"

Carthage

To install it via Carthage, add the following line to your Cartfile and follow the instructions to adding frameworks to an application:

github "e-Sixt/Swen"

Swift Package Manager

To install it using the Swift Package Manager, either directly add it to your project using Xcode 11, or specify it as dependency in the Package.swift file:

// ...
dependencies: [
    .package(url: "https://github.com/e-Sixt/Swen.git", from: "2.0.0"),
],
//...

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Requirements

• iOS 9.0+ / macOS 10.10+ / tvOS 9.0+ / watchOS 2.0+
• Xcode 8.1+
• Swift 3.0+

Usage

import Swen

struct TestEvent: Event {
    let name: String
}

class TestViewController: UIViewController {

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        //register for incoming events
        Swen<TestEvent>.register(self) { event in
            print(event.name)
        }
        //post event
        Swen.post(TestEvent(name: "Sixt"))
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        //unregister from events
        Swen<TestEvent>.unregister(self)
    }
}

Register on different threads

// Registers on the main thread
Swen<Event>.register(_ observer: AnyObject, handler: (_ event: Event) -> Void)

// Registers on background queue
Swen<Event>.registerOnBackground(_ observer: AnyObject, handler: (_ event: Event) -> Void)

// Registers the closure on a specific queue
Swen<Event>.register(_ observer: AnyObject, onQueue queue: OperationQueue, handler: (_ event: Event) -> Void)

Sticky events

Sometimes events carry information that is not only important for that one moment but needs to be kept around longer. For these cases sticky events come in handy. They behave the same as normal events with two further additions. First you can query them by:

struct TestStickyEvent: StickyEvent {
    let name: String
}

print(Swen<TestStickyEvent>.sticky()?.name)

Important: The return sticky is optional, because the event may not be posted yet!

The second additions is that if you register for a sticky event and one was already posted before. It will immediately trigger the registered closure

class TestViewController: UIViewController {

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        //post event
        Swen.post(TestStickyEvent(name: "Stick it"))

        //register for incoming events
        Swen<TestStickyEvent>.register(self) { event in
            print(event.name)
        }
    }
}

System Events

To use System Events, write wrapper for interest NSNotifications:

public struct SystemEvents {

    struct ApplicationWillEnterForeground: Event {
    }

    static func register(storage: SwenStorage = .defaultStorage) {

        let center = NotificationCenter.default

        center.addObserver(forName: .UIApplicationWillEnterForeground, object: nil, queue: nil) { _ in

            Swen.post(ApplicationWillEnterForeground(), in: storage)
        }
    }
}

Dependency Injection

To encapsulate test cases from production code and from each other, we suggest to use Dependency Injection and Storage mechanism:

class TestViewController: UIViewController {

    var swenStorage = SwenStorage()
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        //register for incoming events in custom storage
        Swen<TestEvent>.register(self, in: swenStorage) { event in
            print(event.name)
        }

        //register for incoming events in default storage
        Swen<TestEvent>.register(self) { event in
            print(event.name)
        }

        //post event in custom storage
        Swen.post(TestEvent(name: "Sixt, custom storage"), in: swenStorage)

        //post event in default storage
        Swen.post(TestEvent(name: "Sixt, default storage"))
    }
}

Performance

One of the other main benefits of using Swen is the significant performance increase over NSNotificationCenter

Performance Test	NSNotificationCenter	SwiftBus
Perform 10ˆ6 Events to 1 receiver	6.54s	2.61s
Perform 10ˆ3 Events to 10ˆ3 receivers	14.42s	11.15s

Author

• e-Sixt, sixtlabs@sixt.com

Contributors:

• Dmitry Poznukhov, dmitry.poznukhov@sixt.com
• Franz Busch, franz-joseph.busch@sixt.com
• Dedicated to Sven Röder

License

Swen is available under the MIT license. See the LICENSE file for more info.