Wednesday, October 31, 2018

Notification Protocols from Swift

When I introduced Notification Protocols, I mentioned that they should be Usable from Swift.

This is code from a sample Swift Playground that shows how to do this. The Playground needs to have access to MPWFoundation, for example by being inside a Xcode workspace that includes it.

import Foundation
import MPWFoundation

@objc protocol ModelDidChange:MPWNotificationProtocol {
    func modelDidChange( payload:NSNotification );

class MyView : NSObject,ModelDidChange {
    override public init() {
    func modelDidChange( payload:NSNotification ) {
        print("I was notified, self: \(self) payload: \"\(payload.object!)\"")

let target1 = MyView()
let target2 = MyView()

sendProtocolNotification( ModelDidChange.self , "The Payload")

A brief walkthrough:
  1. We declare a ModelDidChange notification protocol.
  2. We indicate that it is a notification protocol by adopting MPWNotificationProtocol.
  3. The notification protocol has the message modelDidChange
  4. We declare that MyView conforms to ModelDidChange. This means we declaratively indicate that we receive ModelDidChange notifications, which will result in MyView instance being sent modelDidChange() messages.
  5. It also means that we have to implement modelDidChange(), which will be checked by the compiler.
  6. We need to call installProtocolNotifications() in order to activate the declared relationships.
  7. We use sendProtocolNotification() with the Protocol object as the argument and a payload.
  8. The fact that we need a protocol object instead of any old String gives us additional checking.

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