Passing an object between view controllers - ios

Question

Lately I have been working on a new app and I'm struggling to pass data between view controllers.
I use a view controller which holds a container view in which I use google maps. As some of you know it's impossible to put a button on google maps as it overlays everything (that why I put it as a container view). Now I got a problem that I can't make an action button that can performSegue and I also failed to pass an object with the NotificationCenter. I made a model called Song and I want to pass a song List to other controller (a table view).
class Song {
var sid: String
var songName: String
var artistId: String
var length: String
var songImage: String?
var album: String
var lastUpdate:Date? }
Any ideas or suggestions to move this list between VCs?
There is no real connection between those views though, the mainVC is holding them both as containers.

Answer 1

So you have MainController that own both of your controllers that had to exchange data? On way is to use Delegate pattern and setup weak relationsships between your controllers:
protocol SongSelectable {
func songSelected(_ song: Song)
}
class PlaylistController: UIViewController {
weak var songSelectable: SongSelectable?
}
class MapController: UIViewController, SongSelectable {
func songSelected(_ song: Song) {
//do your code
}
}
class MainController: UIViewController {
weak var mapController: MapController?
weak var playlistController: PlaylistController?
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
// You can't guaranty order here, so some duplication required
if let controller = segue as? MapController {
mapController = controller
playlistController?.songSelectable = controller
}
else if let controller = segue as? PlaylistController {
playlistController = controller
controller.songSelectable = mapController
}
}
}
Another option: establish connection via blocks. It is more modern and Swifty way:
typealias SongHandler = (Song)->()
class PlaylistController: UIViewController {
var songHandler = SongHandler?
}
class MapController: UIViewController {
func songSelected(_ song: Song) {
//do your code
}
}
class MainController: UIViewController {
weak var mapController: MapController?
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let controller = segue as? MapController {
mapController = controller
}
else if let controller = segue as? PlaylistController {
controller.songHandler = { [unowned self] (song) in self.mapController?.songSelected(song)
}
}
}
Mind that code fragments above is just illustrations, you have plenty of ways to access controllers, setup delegation or blocks.