TypedNotification

TypedNotification is a Swift library that adds some type-safety to Foundation’s NotificationCenter. The library is small and can be added to your project either as a framework or by directly including the single source file.

Usage

Reference documentation is available here.

Playground

This repository includes an annotated playground that demonstrates the features of TypedNotification. To use it:

1. Clone the repository.
2. Open TypedNotification.xcworkspace
3. Build the TypedNotification scheme for your Mac.
4. Open the Demo playground and run it.

Overview

For each notification in your application, create a new type that conforms to the TypedNotification protocol:

struct DataStoreDidSaveNotification: TypedNotification {

    /// The data store posting the notification.
    let object: DataStore // <- This property is required by the protocol.

    let insertedObjects: Set<Model>
}

When conforming, you must provide a type and the storage for an object attached to the notification. Additional data that would normally be included in a notification’s userInfo dictionary can be provided as properties on the notification.

To post a notification, create an instance of the notification and call post(_:) on a NotificationCenter:

NotificationCenter.default.post(DataStoreDidSaveNotification(object: dataStore, insertedObjects: insertedObjects))

To observe a notification use the addObserver(forType:object:queue:using) method on NotificationCenter. This is similar to the Foundation method but takes a type of notification to observe instead of the name and returns a NotificationObservation to manage the observation:

let observation = NotificationCenter.default.addObserver(forType: DataStoreDidSaveNotification.self, object: nil, queue: nil) { note in
    print(note.insertedObjects)
}

Note that the type of note passed to the callback block is a DataStoreDidSaveNotification.

The returned NotificationObservation instance manages the lifetime of the observation. When the instance is deallocated, the observation stops.

Notification Observation Bags

TypedNotification provides a convenient type for working with NotificationObservations. A NotificationObservationBag stores multiple observation instances and removes them all when deallocated. You can use this to tie the lifetime of an observation to another object:

class ViewController: UIViewController {

    let notificationBag = NotificationObservationBag()

    override func viewDidLoad() {
        super.viewDidLoad()

        NotificationCenter.default.addObserver(forType: DataStoreDidSaveNotification.self, object: nil, queue: nil) { [unowned self] note in
              self.doSomething(with: note.insertedObjects)
          }
          .stored(in: notificationBag)
    }
}

Here, when a ViewController is deallocated, so to is its notification bag and the observation set up in viewDidLoad() goes away.

This is really useful behaviour so TypedNotification includes a variant of addObserver for normal Notifications that also returns a NotificationObservation:

func setUpKeyboardObservation() {
    NotificationCenter.default.addObserver(forNotificationNamed: UIWindow.keyboardWillShowNotification, object: nil, queue: nil) { note in
            print(note.userInfo?[UIWindow.keyboardFrameEndUserInfoKey])
        }
        .stored(in: notificationBag)
}

Requirements & Installation

TypedNotification requires a version of Xcode that can compile Swift 5 code. Additionally it requires a deployment target targeting iOS 10+ or macOS 10.12+ because of a dependency on os.lock.

You’ve got four options for installation.

Manual Installation

Copy TypedNotification.swift from the Sources directory.

CocoaPods

Add the following to your Podfile:

pod 'AJJTypedNotification', '~> 2.0'

Note that the name of the module (i.e., what you import) is TypedNotification but the pod is AJJTypedNotification.

Carthage

Add the following to your Cartfile:

github "alexjohnj/TypedNotification" ~> 2.0

Swift Package Manager

Add the following to your Package.swift file’s dependencies:

dependencies: [
    .package(url: "https://github.com/alexjohnj/TypedNotification.git", .upToNextMinor(from: "2.0.0"))
]

License

MIT