Announcements

An implementation of Announcements in swift.

Announcements promote the use of first class objects when using the Observer mechanism, a more expressive publish/subscribe mechanism than using plain strings, they originally come from the Smalltalk programming language.

Example

The example makes use the "Presenter First" approach (see atomic_object) that promotes presenters (the P in MVP) to a principal role, when tackling the design and implementation of an applications view layer.

The app is an simple person list, with a built-in chooser implemented via a segemented control, to showcase the use of Announcements as a means to syncrhonize between models and views via a mediator, i.e: PersonListPresenter and PersonViewPresenter.

Note: we use a wrapper around UIControl, to adapt the addTarget:action:for: style to when:do:

In the view controller we initialise the presenters (first)

 override func viewDidLoad() {
        super.viewDidLoad()
        listPresenter = PersonListPresenter(listModel: personList, segmentedControl: segmentedControl)
        viewPresenter = PersonViewPresenter(listModel: personList, personView: personView)
    }

where each presenter stitches the model and the view using the when:do style as follows

        listModel.listener.when(ann: .selectionChanged) { ann in
            switch ann {
            case .selectionChanged:
                personView.configure(person: listModel.selectedPerson!)
            }
        }

and annoucements will eventually get triggered whenever we change the list model:

  func select(at: Int) {
        selectedIndex = at
        announcer.announce(ann: .selectionChanged)
    }