Extending NotificationCenter - ios

Question

I am trying to write an extension for NotificationCenter
I find the syntax a little meaty and "boilerplatey" and would like to provide a simple extension that simplifies posting and observing.
I can dispatch an event like so
NotificationCenter.dispatch(key: <#T##String#>, payload: <#T##[String : String]#>)
However I would like to observe an event in a similar fashion.
I am trying to create something like
NotificationCenter.observe(key: <#T##String#>, handler: <#T##() -> Void#>)
However this is not correct. I am unsure how I can handler passing in my selector function that should be triggered on an observation?
This is my attempt so far.
extension NotificationCenter {
static func dispatch(key: String, payload: [String: String] = [:]) {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: key), object: nil, userInfo: payload)
}
static func observe(key: String, handler: ()->Void) {
NotificationCenter.default.addObserver(
self, selector: handler, name: NSNotification.Name(rawValue: key), object: nil
)
}
}

Answer 1

It sounds like you need something like
extension NotificationCenter {
static func dispatch(key: String, payload: [String: String] = [:]) {
self.default.post(name: NSNotification.Name(rawValue: key), object: nil, userInfo: payload)
}
static func observe(key: String, handler: #escaping (Notification) -> Void) {
self.default.addObserver(forName: NSNotification.Name(rawValue: key), object: nil, queue: .main, using: handler)
}
}

Answer 2

You can use something like this:
extension NotificationCenter {
class func observe(name: NSNotification.Name, handler: #escaping (Notification) -> Void) {
self.default.addObserver(forName: name, object: nil, queue: .main, using: handler)
}
}
Then you can use it like this:
NotificationCenter.observe(name: UIResponder.keyboardDidShowNotification) { notification in
// do something
}
You should definitely check out https://developer.apple.com/documentation/foundation/notificationcenter/1411723-addobserver regarding unregistering observations though.

Answer 3

NotificationCenter - a useful but bulky looking interface, feels a bit bloating in code, as someone coming from UNIX-like thread synchronization semantics... So, these extensions are based on stuff on S.O. & the 'Net, with a couple of twists.
extension Notification.Name {
static let patientlyWaiting = Notification.Name("patientlyWaiting")
// .
// . list your arbitrary waiter names here...
// .
}
extension NotificationCenter {
static func wait(_ name : Notification.Name) async {
for await _ in NotificationCenter.default.notifications(named: name) {
break;
}
}
static func post(_ name : Notification.Name) {
NotificationCenter.default.post(name: name, object: nil)
}
static func postProcessing(_ name: Notification.Name, using block: #escaping (Notification) -> Void) {
NotificationCenter.default.addObserver(forName: name, object: nil, queue: OperationQueue.main, using: block)
}
}
To use it, something like this:
Waiting for notification:
#IBAction func doSomethingAsychronouslyButtonPushed(_ sender: Any) {
doSomethingAsynchronously()
NotificationCenter.postProcessing(.patientlyWaiting, using: { _ in
print("doSomethingAsynchronouslyButton completion handler called")
})
}
Notifying:
func doSomethingAsynchronously() {
for n in ["Time", " ", "consuming", " - ", "whatever"] {
print("\(n)", terminator: "")
}
print("\n")
NotificationCenter.post(.patientlyWaiting)
}
Note: You could avoid using a closure and do an inline wait using Swift language's recently-added async/await support (see the 'wait()function in the extensions shown above), but I didn't provide an example of using that because I haven't been able to invokeasyncfunctions from selectors, such as from aUIButtonpress, directly or indirectly; because, any function that usesawaitneeds to be declaredasync. Specifically, #selector(afunc(_:)) doesn't match functions declared async, and I'm unaware of a function signature syntax that accounts for an asyncin function declaration (to pass to#selector()`). If someone knows, let me know in the comments and I'll update the answer.