Better Notification & Key Value Observers for Swift.
- Simpler API with sensible defaults
- Easier to avoid 'dangling' observers
- Easy activation/deactivation
- Simple integration with view controller lifecycles
HSObserver is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod 'HSObserver'Or Install as a swift package
class Watcher {
static let wave = NSNotification.Name.init("waveNotification")
var waveObserver:HSObserver
init() {
waveObserver = HSObserver.init(forName: Watcher.wave,
activate:true,
using: { (notif) in
//Do Something
})
}
}Unlike a standard observer, waveObserver is fully released when Watcher is released.
(Posting a wave notification will not call the //Do Something code once Watcher is released)
var waveObserver:HSObserver
init() {
waveObserver = HSObserver.init(forName: Watcher.wave,
using: { (notif) in
//Do Something
})
//activate
waveObserver.activate()
//deactivate
waveObserver.deactivate()
}N.B. Remember that you have to activate your observer for it to work.
- either specify
activate:truein the initialiser - or call myObserver.activate()`
- or chain on the initialiser
HSObserver.init(....).activate()
A common pattern for a view controller is to activate observers in viewWillAppear, and de-activate them in viewDidDisppear
Adding the HSHasObservers protocol to any class allows you to add a group of observers, and activate or deactivate them easily.
Observers can be added manually, or by chaining .add(to:self) to an HSObserver
class ViewController: NSViewController, HSHasObservers {
override func viewDidLoad() {
super.viewDidLoad()
//Add manually
let waveObserver = HSObserver.init(forName: Watcher.wave,
using: { (notif) in
//Do Something
})
self.add(observer: waveObserver)
//Or by chaining
HSObserver.init(forName: Watcher.wave,
using: { (notif) in
//Do Something
}).add(to: self)
}
}this works well with the view lifecycle
override func viewWillAppear() {
super.viewWillAppear()
activateObservers()
}
override func viewDidDisappear() {
super.viewDidDisappear()
deactivateObservers()
} let manyThingsObserver = HSObserver.init(forNames: [Watcher.wave,Watcher.hello] ,
activate:true,
using: { (notif) in
//Do Something
}) /// Create observer
///
/// - parameter name: notification name
/// - parameter obj: object to observe (default nil)
/// - parameter queue: queue to run the block on (default main)
/// - parameter center: notification center (default NotificationCenter.default)
/// - parameter block: block to run (beware of retain cycles!)
///
/// - returns: unactivated manager. Call activate() to start
convenience init(forName name: NSNotification.Name,
object obj: Any? = nil,
queue: OperationQueue? = .main,
center newCenter: NotificationCenter = NotificationCenter.default,
activate: Bool = false,
using block: @escaping (Notification) -> Swift.Void)HSObservers lets you skip the defaults. We assume
- object = nil
- queue = .main
- center = NotificationCenter.default
- activate = false
you can override each of these in the initialiser
Note that Apple's default is to call your block on the same queue as the sender. If you want to do this, then just use centre = nil
I find that I typically want to use notifications to update the UI - so my default is to use .main
Post a notification directly
class Watcher {
struct Notif {
static let wave = NSNotification.Name.init("waveNotification")
}
func doPosting() {
Watcher.Notif.wave.post()
//or
Watcher.Notif.wave.post(object:self,userInfo:["Foo":"Bar"])
}
}Assume the default notification centre and default options when posting directly from NotificationCenter (I strongly reccomend that you structure your notifications within a Notif struct of the relevant object. It makes things really easy to read)
NotificationCenter.post(Watcher.Notif.wave)
//is equivalent to
NotificationCenter.default.post(Watcher.wave,object:nil)for example, to observe the duration of an AVPlayerItem
durationObserver = HSKeyPathObserver.init(forKeyPath: "duration",
of: item,
activate:true) {
[weak self](_) in
self?.generateImages()
}(again, remember to keep a reference to durationObserver or it will disappear)
ConfusedVorlon, rob@hobbyistsoftware.com
HSNotification is available under the MIT license. See the LICENSE file for more info.